Broadbalk

  • Experiment Code: R/BK/1
  • Experiment Site: Rothamsted
  • Objectives: To test the effect of different organic manures and inorganic fertilizers on the yield of winter wheat.
  • Description: Started in 1843, Broadbalk is one of the oldest continuous agronomic experiments in the world. Wheat is grown every year on all or part of the experiment. Established to test the effects of various combinations of inorganic fertilizers (N, P, K, Na and Mg) and organic manures on the yield of winter wheat, many of these treatments continue today. A control strip has received no fertilizer or organic manures since 1843. It was started by Lawes and Gilbert in autumn 1843, and the first crop was harvested in summer 1844.
  • Date Start: 1843
  • Establisment Period End: 1851
  • Date End: Ongoing

Key Contacts

  • Andrew Gregory

  • Role: Principal Investigator
  • ORCID: https://orcid.org/0000-0001-7123-0784
  • Organisation: Rothamsted Research
  • Address: West Common, Harpenden, Hertfordshire, AL5 2JQ, United Kingdom
  • Sarah Perryman

  • Role: Data Manager
  • Organisation: Rothamsted Research
  • Address: West Common, Harpenden, Hertfordshire, AL5 2JQ, United Kingdom
  • Margaret Glendining

  • Role: Data Manager
  • ORCID: https://orcid.org/0000-0002-6466-4629
  • Organisation: Rothamsted Research
  • Address: West Common, Harpenden, Hertfordshire, AL5 2JQ, United Kingdom

Funding

Experimental Design

Description

  • The experiment was divided into different Strips or 'Plots' (2 - 20) receiving the different fertilizer and manure treatments each year. Most treatment strips were established by 1852, except for strip 2a (2.1), which began in 1885, and strip 20, which began in 1906. Plot 19 was originally a half plot, and became its current size in 1904. Between 1894 and 1925 many plots were harvested in two halves, Top (T) and Bottom (B), equivalent to the Western and Eastern parts of the experiment.

Design

  • Period: 1852 - 1925
  • Number of Blocks: 19
  • Number of Replicates: 1
  • Number of Harvests per Year: 1

Crops

Crop Years Grown
Winter Wheat

Factors

Factors are the interventions or treatments which vary across the experiment.

Nitrogen Fertilizer Exposure

Description: Inorganic nitrogen fertilizer in various forms and amounts applied annually

Application: Whole Plot

Levels
Level Name Amount Years Frequency Crop Method Chemical Form Notes
N1 48 kgN/ha 1852 - 1925 winter wheat broadcast application method ammonium sulfate All applied in autumn, 1852-1877, all applied in spring 1878-1883; 24 kgN applied in autumn, remainder applied in spring 1884-1925
N1* 48 kgN/ha 1852 - 1925 winter wheat broadcast application method sodium nitrate All applied in spring, as one application until 1898, as two equal amounts 1899-1925
N1. 5 72 kgN/ha 1852 - 1878 winter wheat broadcast application method ammonium sulfate Applied to Plot 19 with rape cake, All applied in autumn
N2 96 kgN/ha 1852 - 1925 winter wheat broadcast application method ammonium sulfate All applied in autumn, 1852-1877, all applied in spring 1878-1883; 24 kgN applied in autumn, remainder applied in spring 1884-1925, except to strip 15. Strip 15 N applied in spring 1873-77, N applied in autumn 1878-1925.
N2* 96 kgN/ha 1852 - 1925 winter wheat broadcast application method sodium nitrate All applied in spring, as one application until 1898, as two equal amounts 1899-1925
N3 144 kgN/ha 1852 - 1925 winter wheat broadcast application method ammonium sulfate All applied in autumn, 1852-1877, all applied in spring 1878-1883; 24 kgN applied in autumn, remainder applied in spring 1884-1925
N4 192 kgN/ha 1852 - 1864 annually winter wheat broadcast application method ammonium sulfate All applied in autumn

Farmyard Manure Exposure

Description: FYM from cattle

Levels
Level Name Amount Years Frequency Crop Method Chemical Form Notes
Farmyard Manure 35 t/ha 1843 - 1925 Annual winter wheat Applied to plot 2b (2.2) from 1843, and to plot 2a (2.1) since 1885. Plot 2a was a new plot made in 1885. FYM is applied in autumn, supplying approx 225 kgN

Phosphate Fertilizer Exposure

Description: phosphate fertilizer

Levels
Level Name Amount Years Frequency Crop Method Chemical Form Notes
P 35 kg/ha 1843 - 1925 annually winter wheat chemical basal application triple superphosphate Applied in the autumn, omitted 1915

Potassium Fertilizer Exposure

Description: Potassium fertilizer application

Levels
Level Name Amount Years Frequency Crop Method Chemical Form Notes
K 90 kg/ha 1843 - 1925 annually winter wheat fertilizer basal application potassium sulphate Applied in the autumn, omitted 1915, 1917-1919

Sodium Nutrient Exposure

Description: sodium fertilizer application

Levels
Level Name Amount Years Frequency Crop Method Chemical Form Notes
Na 16 kg/ha 1843 - 1925 annually winter wheat fertilizer basal application sodium sulphate Applied in the autumn, omitted 1915

Magnesium Nutrient Exposure

Description: Magnesium fertilizer application

Levels
Level Name Amount Years Frequency Crop Method Chemical Form Notes
Mg 11 kg/ha 1843 - 1925 annually winter wheat fertilizer basal application magnesium sulphate Applied in the autumn, omitted 1915

Rapeseed Cake Exposure

Description: Organic manure supplying approx 96 kgN

Levels
Level Name Amount Years Frequency Crop Method Chemical Form Notes
C 96 kgN/ha 1852 - 1926 annually winter wheat Supplying approx 96 kg N (N2).

Factor Combinations

Factor Combinations are the combination of factors applied to different plots on the experiment.

Factor Combination Time Coverage Notes
FYM 1885 - 1925 Applied to plot 2a (2.1), which was created in 1885.
FYM 1843 - 1925 Applied to plot 2b (2.2), originally called plot 2, named plot 2b in 1885 when plot 2a was created.
Nil 1843 - 1925 Strip 3. Originally 2 half plots, 3 (nil since 1844) and 4 (1844-51 NP; since 1852 nil). Harvested separately until 1899. Strip 16 received nil 1865-1883
PKNaMg 1843 - 1925 Strip 5
N1 PKNaMg 1843 - 1925 Strip 6
N2 PKNaMg 1852 - 1925 Strip 7, also Strip 15a 1852-1872, Strip 15 1873-1925, but N applied at different times to strip 7. Strip 15 was divided into 15a and 15b which received different fertilizer treatments until 1873.
N3 PKNaMg 1852 - 1925 Strip 8
N1* PKNaMg 1894 - 1925 Strip 9, split into 9a and 9b, 1852-1893 receiving different treatments. 9a received N1*/N2* plus PKNaMg, 9b received only N2*/N1*.
N4 PKNaMg 1852 - 1864 Strip 16, which then received nil 1865-1883 and N2*PKNaMg since 1884
N2* PKNaMg 1884 - 1925 Strip 16; previously received N4 PKNaMg (1852-1864) and nil (1865-1883)
N1.5 PKNaMg +C 1852 - 1872 Strip 15b. After 1872 strip 15a and 15b combined and received the same fertilizer treatments N2 PKNaMg

Measurements

Variable Unit Collection
Frequency
Material Description Crop
Yield Components t/ha annually SpecifiedCrop Grain and straw yields at field moisture content. Actual dry matter not measured, assumed to be approximately 85% dry matter. winter wheat
Weight per Bushel Dressed Corn lb annually SpecifiedCrop Bushel weights can be used to derive Hectolitre weights (HLWT),a measure of grain quality. winter wheat
Soil Organic Carbon % infrequently Soil Topsoil (0-23cm) from soil sampled in 1865, 1881, 1893 and 1914.
Soil Organic Carbon t/ha infreqently Soil Topsoil (0-23cm) from soil sampled in 1865, 1881, 1893 and 1914. Calculated from % SOC and soil bulk density; adjusted for changes in bulk density in strips given FYM
Soil Total Nitrogen % infrequently Soil Topsoil (0-23cm) from soil sampled in 1865, 1881, 1893 and 1914.
Plant Available Phosphorous mg/kg infrequently Soil Sodium bicarbonate soluble P (Olsen P). Topsoil (0-23cm) from soil sampled in 1865, 1881, 1893 and 1914.
Soil Bulk Density g/cm3 infrequently Soil A single mean value for all plots which do not receive FYM and estimated values for plots which receive FYM, based on measurements made in 1865, 1881, 1893 (Dyer, 1902), 1914 (unpublished) and 2000 (Watts et al, 2006).
Harvest Date annually SpecifiedCrop Includes both cutting and carting date, ie dates crop cut and then removed from the field. winter wheat

Description

  • 19 fertilizer treatment strips divided into five sections in 1926 (I-V) crossing all the treatment strips. In 1955 Section I was divided into Ia and Ib; Ia in continuous wheat, no fallow, Ib continued in the fallow rotation. In 1955 Section V was divided into Va and Vb. Va continued in the fallow rotation, with no herbicides applied. Vb received lime in 1955, and became continuous wheat with no further fallows from 1959.

Design

  • Period: 1926 - 1967
  • Number of Blocks: 19
  • Number of Sub-plots:
  • Number of Harvests per Year: 1

Crops

Crop Years Grown
Winter Wheat
Fallow

Factors

Factors are the interventions or treatments which vary across the experiment.

Nitrogen Fertilizer Exposure

Description: Inorganic nitrogen fertilizer in various forms and amounts applied annually

Levels
Level Name Amount Years Frequency Crop Method Chemical Form Notes
N1 48 kg/ha 1926 - 1967 twice winter wheat broadcast application method ammonium sulfate 24kgN applied in autumn, remainder in spring
N2 96 kg/ha 1926 - 1967 twice winter wheat broadcast application method ammonium sulfate 24kgN applied in autumn, remainder in spring
N3 144 kg/ha 1926 - 1967 twice winter wheat broadcast application method ammonium sulfate 24kgN applied in autumn, remainder in spring
N1* 48 kg/ha 1926 - 1967 twice winter wheat broadcast application method sodium nitrate Applied in spring as two equal amounts
N2* 96 kg/ha 1926 - 1967 twice winter wheat broadcast application method sodium nitrate Applied in spring as two equal amounts

Farmyard Manure Exposure

Description: FYM from cattle

Levels
Level Name Amount Years Frequency Crop Method Chemical Form Notes
Farmyard Manure 35 t/ha 1926 - 1967 Once a year winter wheat Applied to strips 2.1 (2a) and 2.2 (2b). Not applied in the fallow years

Factor Combinations

Factor Combinations are the combination of factors applied to different plots on the experiment.

Factor Combination Time Coverage Notes
FYM 1926 - 1965

Measurements

Variable Unit Collection
Frequency
Material Description Crop
Yield Components t/ha annually SpecifiedCrop Grain and straw yields at field moisture content, approximately 85% dry matter. winter wheat
Weight per Bushel Dressed Corn lb annually SpecifiedCrop Bushel weights can be used to derive hectolitre weights (HLWT), a measure of grain quality winter wheat
Soil Organic Carbon % infrequently Soil Topsoil (0-23cm) from soil sampled in 1936; 1944 and 1966.
Total Soil Nitrogen % infrequently Soil Topsoil (0-23cm) from soil sampled in 1936; 1944 and 1966.
Plant Available Phosphorous mg/kg infrequently Soil Sodium bicarbonate soluble P (Olsen P). Topsoil (0-23cm) from soil sampled in 1936, 1944 and 1966
Soil Bulk Density g/cm3 infrequently Soil A single mean value for all plots which do not receive FYM and estimated values for plots which receive FYM, based on measurements made in 1865, 1881, 1893 (Dyer, 1902), 1914 (unpublished) and 2000 (Watts et al, 2006).
Soil Organic Carbon t/ha infrequently Soil Topsoil (0-23cm) from soil sampled in 1936, 1944 and 1966. Calculated from % SOC and soil bulk density; adjusted for changes in bulk density in strips given FYM
Weed Species Richness Species occurence, selected plots and selected years for all sections (before herbicides were applied)
Harvest Date annually SpecifiedCrop Both cutting date and carting date (ie date crop removed from field) winter wheat

Description

  • Two major modifications were made from 1968: i) The division of Sections I to V to create 10 new Sections (0 - 9), so the yield of wheat grown continuously could be compared with that of wheat grown in rotation after a two-year break. ii) The introduction of modern, short-strawed cultivars, which lead to an increase in grain yields and a decrease in straw yields. The old cultivar Squarehead's Master was grown on parts of some plots between 1987 and 1990, enabling a comparison to be made with modern cultivars After the 1968 changes, Sections 0, 1, 8 and 9 continued to grow winter wheat only, whilst Sections 2, 4, 7 and Sections 3, 5, 6 went into two different 3-course rotations (see 1968 cropping details link). In 1978, Section 6 reverted to continuous wheat and the other five Sections went into a five year rotation. Pesticides are applied where necessary, except on Section 6, which does not receive spring or summer fungicides. Herbicides have been used as required since 1964 on all of the experiment, except for Section 8 (old Section VA), which has never received herbicides. On Section 0 the straw on each plot has been chopped after harvest and incorporated in the soil since autumn 1986; on all other Sections the straw is baled and removed. In 1993 Section 9 was re-drained so that water leaching through the soil could again be collected and analysed. Lime has been applied as required since the 1950s to maintain soil pH at a level at which crop yield is not limited. From 2001 P has not been applied to some plots until levels of plant available P decrease to more appropriate agronomic levels. This is reviewed each year.

Design

  • Period: 1968 - Now
  • Number of Harvests per Year: 1

Crops

Crop Years Grown
Winter Wheat1968 -
Oats1996 -
Spring Beans1968 - 1978
Potatoes1968 - 1996
Winter Beans2018 -
Fallow
Maize1997 - 2017

Crop Rotations

Rotation Crops
continuous wheat (1968 - ) Winter Wheat
P-BE-W (1968 - 1979) Potatoes > Spring Beans > Winter Wheat
F-W-W (1968 - 1981) Fallow > Winter Wheat > Winter Wheat
F-P-W (1979 - 1983) Fallow > Potatoes > Winter Wheat
F-P-W-W-W (1982 - 1999) Fallow > Potatoes > Winter Wheat > Winter Wheat > Winter Wheat
O-M-W-W-W (1996 - 2017) Oats > Maize > Winter Wheat > Winter Wheat > Winter Wheat
W-W-O-W-Be (2018 - ) Winter Wheat > Winter Wheat > Oats > Winter Wheat > Winter Beans

Factors

Factors are the interventions or treatments which vary across the experiment.

Nitrogen Fertilizer Exposure

Description: N was applied as calcium ammonium nitrate (Nitro-chalk) 1968-1985. Between 1968-1996 N was applied at the same rate to beans and potatoes, no N to fallow. 1996-2017 oats did not receive N. 1997-2017 split N treatments were applied to forage maize, in the seedbed and post-emergence. Since 2018 oats received N at half the normal rate. No N applied to beans from 2018.

Application: Whole Plot

Levels
Level Name Amount Years Frequency Crop Method Chemical Form Notes
N1 48 kgN/ha 1968 - annually in mid-April winter wheat ammonium nitrate
N2 96 kgN/ha 1968 - annually in mid-April winter wheat ammonium nitrate
N3 144 kgN/ha 1968 - annually in mid-April winter wheat ammonium nitrate
N4 192 kgN/ha 1968 - annually in mid-April winter wheat ammonium nitrate
N5 240 kgN/ha 1985 - annually in mid-April winter wheat ammonium nitrate
N6 288 kgN/ha 1985 - annually in mid-April winter wheat ammonium nitrate
N1+1+1 144 kgN/ha 2001 - mid-March, mid-April, Mid-May winter wheat ammonium nitrate N2+1 for maize 1997-2017
N1+2+1 192 kgN/ha 2001 - mid-March, mid-April, Mid-May winter wheat ammonium nitrate N2+2 for maize 1997-2017
N1+3+1 240 kgN/ha 2001 - mid-March, mid-April, Mid-May winter wheat ammonium nitrate N2+3 for maize 1997-2017
N1+4+1 288 kgN/ha 2001 - mid-March, mid-April, Mid-May winter wheat ammonium nitrate N2+4 for maize

Potassium Fertilizer Exposure

Application: Whole Plot

Levels
Level Name Amount Years Frequency Crop Method Chemical Form Notes
K 90 kgK/ha 1968 - annually in autumn potassium sulphate
K2 180 kgK/ha 2001 - 2005 annually in autumn potassium sulphate
K* 90 kgK/ha 2001 - Annually in autumn potassium chloride

Phosphate Fertilizer Exposure

Description: P fertilizer no longer applied to some plots since 2000 due to high levels of soil P. Indicated as (P).

Application: Whole Plot

Levels
Level Name Amount Years Frequency Crop Method Chemical Form Notes
P 35 kgP/ha 1968 - Annually in autumn calcium bis(dihydrogenphosphate)

Sodium Nutrient Exposure

Application: Whole Plot

Levels
Level Name Amount Years Frequency Crop Method Chemical Form Notes
Na1 16 kgNa/ha 1968 - 1973 Annually in autumn sodium sulphate
Na2 55 kgNa/ha 1968 - 2000 Annually in autumn sodium sulphate 57 kgNa/ha until 1973

Magnesium Nutrient Exposure

Application: Whole Plot

Levels
Level Name Amount Years Frequency Crop Method Chemical Form Notes
Mg 12 kgMg/ha 1968 - Annually in autumn magnesium sulphate 11kgMg until 1973. 35 kgMg every 3rd year 1974-2000.
Mg2 24 kgMg/ha 2001 - 2005 Annually in autumn magnesium sulphate Plus 60 kg Mg in autumn 2000 only
Mg* 30 kgMg/ha 1968 - 2000 Annually in autumn magnesium sulphate 31kgMg as magnesium sulphate until 1973

Farmyard Manure Exposure

Description: From cattle

Application: Whole Plot

Levels
Level Name Amount Years Frequency Crop Method Chemical Form Notes
Fym 35 t/ha 1968 - Annually in autumn winter wheat Derived from cattle. Not applied to beans from 2018, not applied to oats 1996-2017.
Residual Fym 2001 - Plots previously receiving FYM

Castor Meal Exposure

Description: Plots previously receiving Castor Mean indicated as (C)

Application: Whole Plot

Levels
Level Name Amount Years Frequency Crop Method Chemical Form Notes
C 96 kgN/ha 1968 - 1988 annually

Factor Combinations

Factor Combinations are the combination of factors applied to different plots on the experiment.

Factor Combination Time Coverage Notes
FYM N2 PK 1968 - 1984 Applied to strip 01
FYM N4 PK 1985 - 2000 Applied to strip 01
(FYM) N4 2001 - Applied to strip 01
FYM N2 1968 - 2004 Applied to strip 2.1
FYM N3 2005 - Applied to strip 2.1
FYM 1968 - Applied to strip 2.2
Nil 1968 - No organic or inorganic amendments, strip 03
(P)K(Na)Mg 1968 - 1973 Applied to strip 05
N1 (P)K(Na)Mg 1968 - Applied to strip 06
N2 (P)K(Na)Mg 1968 - Applied to strip 07 and applied to strip 16 until 1984
N3 (P)K(Na)Mg 1968 - Applied to strip 08, and applied to strip 15 until 1984
N4 (P)K(Na)Mg 1968 - Applied to strip 09
N2 1968 - 2000 Applied to strip 10
N4 2001 - Applied to strip 10
N2 P 1968 - 2000 Applied to strip 11
N4 PMg 2001 - Applied to strip 11
N2 PNa 1968 - 2000 Applied to strip 12
N1+3+1 (P)K2Mg2 2001 - 2005 Applied to strip 12. P was not applied in this period
N1+3+1 (P)KMg 2006 - Applied to plot 12
N2 PK 1968 - 2000 Applied to plot 13
N4 PK 2001 - Applied to strip 14
N2 PKMg* 1968 - 2000 Applied to plot 14
N4 PK* 2001 - Applied to strip 14
N5 (P)KMg 1985 - Applied to strip 15
N6 (P)KMg 1985 - Applied to plot 16
N2 1/2[PK(Na)Mg 1968 - 1984 Applied to strips 17 and 18 in alternate years
N[0|1]+3 1/2[PKMg] 1985 - 2000 Applied to strips 17 and 18 in alternate years
N1+4+1 PKMg 2000 - Applied to strip 17
N1+2+1 PKMg 2001 - Applied to strip 18
C 1968 - 1988 Applied to strip 19
N1+1+1 KMg 2001 - Applied to strip 19
N2 K(Na)Mg 1968 - 2000 Applied to strip 20
N4 KMg 2000 - Applied to strip 20

Measurements

Variable Unit Collection
Frequency
Material Description Crop
Yield Components t/ha annually AllCrops Grain and straw at 85% dry matter.
Hectolitre Grain Weight annually SpecifiedCrop Since 1999 selected plots only winter wheat
Thousand Grain Weight annually SpecifiedCrop Since 1974 selected plots only winter wheat
Weed Species Richness annually Section 8 only (no herbicides)
Soil Organic Carbon every five years from 1987 Soil Topsoil (0-23cm)
Soil Total Nitrogen every five years from 1987 Soil Topsoil (0-23cm)
Plant Available Phosphorous mg/kg every five years for 1987 Soil Topsoil (0-23cm).
Soil Bulk Density Soil A single mean value for all plots which do not receive FYM and estimated values for plots which receive FYM, based on measurements made in 1865, 1881, 1893 (Dyer, 1902), 1914 (unpublished) and 2000 (Watts et al, 2006).
Nutrient Content annually AllCrops Selected plots since 1968 % N, P, K, Ca, Mg, Na and S. Grain and straw.
Take-all Disease Incidence annually SpecifiedCrop Selected plots since 1968. Also eyespot, sharp eyespot and brown foot rot. winter wheat
Harvest Date annually AllCrops Sowing and harvest dates of all crops
Earthworm Abundance occasional Selected plots, occasional years.

Site: Broadbalk - Rothamsted

  • Experiment Site: Rothamsted
  • Description: The site has probably been occupied since Roman times, and the Rothamsted map of 1623 shows the site under arable cultivation. The first experimental crop was harvested in 1844 after a rotation of turnips (dunged) 1839, barley 1840, peas 1841, wheat 1842 and oats 1843. The last four crops being entirely unmanured. The field was therefore considered to be exhausted according to contemporary practice.
  • Management: The site is managed using conventional tillage and pesticide applications are applied as necessary, except for herbicide and fungicide exclusion plots. There is no irrigation. The plough layer (0-23 m) is limed when necessary to maintain a minimum soil pH of 7.0 – 7.5.
  • Visit Permitted?: Yes
  • Visiting Arrangments: Contact Dr Andrew Gregory
  • Elevation: 130 Metres
  • Geolocation:    51.80946, -0.37301

Soil

  • Type: Luvisol
    The soil is classified as a Chromic luvisol. The soil texture is described as clay loam to silty clay loam over clay-with flints. The soils contain a large number of flints and are slightly calcareous. Below about 2m depth the soil becomes chalk. The experiment is under-drained and the site is free draining. There is considerable variation in soil texture across the site, with clay contents ranging from 19 – 39%

Soil Properties

Variable Value Reference Year Is Estimated Is Baseline
Sand content 25% (Percent) NO NO
Silt content 50% (Percent) NO NO
Clay content 25% (Percent) NO NO
Soil organic carbon 1% (Percent) 1843 YES NO
Total soil nitrogen 0.11% (Percent) 1843 YES NO
Plant available phosphorous (Olsen P) 10mg/kg (milligram per kilogram) 1843 YES NO
Soil bulk density 1.25g/cm3 (gram per cubic centimetre) 1843 YES NO
Soil organic carbon 28.8t/ha (tonnes per hectare) YES NO

Datasets available

Title (hover for a longer description) Year of Publication Type Identifier Version

Crop nutrient data

Broadbalk Crop Nutrient Content, Wheat 1968-2017 2021 Summary 10.23637/rbk1-BKNUTRW-01
01

Crop yield data

Broadbalk mean long-term winter wheat yields 2017 Summary 10.23637/KeyRefOABKyields
01
Broadbalk Wheat Experiment mean annual grain and straw yields 1852-1925 2021 Complete (Frictionless) 10.23637/rbk1-1796346264-1
01
Broadbalk Wheat Experiment 10-year mean yields 1852-1967 2023 Summary 10.23637/rbk1-meanyld5267
01
Fisher 1921 Broadbalk wheat grain yields 1852-1918 2018 Summary 10.23637/rbk1-data-fisher-1921-01
01
Broadbalk Wheat Experiment yields and N uptake Section 1, 2001-2015 2022 Complete (Frictionless) 10.23637/rbk1-yldS10115-01
01

Disease data

Broadbalk Wheat Experiment brown foot rot (Fusarium spp.) 1992-2009 2021 Summary 10.23637/rbk1-bfr-01
01

Experiment details

Broadbalk Wheat Experiment Chalk Applications 2022 Complete (Frictionless) 10.23637/rbk1-chalk-01
01

Soil data

Broadbalk soil organic carbon content 1843-2015 2021 Summary 10.23637/KeyRefOABKsoc-02
02
Broadbalk soil organic carbon content 1843-2010 2014 Summary 10.23637/KeyRefOABKsoc
01
Broadbalk Soil Total % Nitrogen Content, 1843-2010 2018 Summary 10.23637/BK-oadata-soilN-01
01
Broadbalk changes in Olsen P in top soil, 1843-2010 2016 Summary 10.23637/keyrefoabkolsenp
01

Species observation data

Cirsium arvense frequency on Broadbalk Section 8 1991-2018 2019 Summary 10.23637/bbk-2078416917-01
01
.

Videos

Video on the Broadbalk Experiment
A visually engaging short film on the Broadbalk experiment.

Images

Experimental plans, fertilizer treatments, chalk, cropping details, and dates of key field operations, 1852-present

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Plans and treatments

Scholastic Dataset

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Lessons from Broadbalk: This activity invloves students plotting graphs and interrogating real wheat yield data from Broadbalk long-term wheat experiment at Rothamsted, Harpenden. It explores the effect of different fertiliser treatments and farming practices on wheat yields. It also encourages students to think about why long-term data is important.

This resource provides instructions for a teacher and an activity sheet with the data for students. It is aimed at KS3 Mathematics students (years 7-9) and ties in with the school curriculum, in terms of interpreting data, considering anomalies and trends.

Schools activity

Information about analytical methods for crop macro nutrient content (% N, P, K, Ca, Mg, Na and S)

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Broadbalk Crop Nutrient Content

The Broadbalk experiment was started in 1843 to investigate the relative importance of the plant nutrients nitrogen, phosphorus, potassium, magnesium and sodium (N, P, K, Mg and Na) on grain yield of winter wheat. From the very start of the experiment, samples of wheat grain and straw were kept from each plot, for chemical analysis, though some early samples were lost because the containers were damaged.

Early analysis

Lawes and Gilbert carried out analyses of wheat grain and straw for N, P, K, Ca, Mg and Na content on proportionally bulked samples from 10 plots, representing four ten-year periods (1852-1861, 1862-1871, 1872-1881 and 1882-1891). The results for crops grown in 1852-1871 were published in detail (Lawes & Gilbert, 1884). However, only the results for P, K, and Na content for four of the 10 plots for the second period (1872-1891) were published (Gilbert, 1895). Johnston (1969) summarises these early analyses.

Johnston (1969) also measured N, P, K, Ca, Mg and Na in grain and straw of the last two crops of Squarehead's Master grown in 1966 and 1967, on samples taken from all plots in the continuous wheat section, last fallowed in 1951, and from all sections carrying the first wheat after fallow. These were compared with samples from 1852-91 (mean of 1966-67 only, not individual values).

1968 to present

In 1968 Broadbalk was divided into 10 sections. It was decided that it was no longer practical to keep samples for chemical analysis from all plots (10 sections x 19 plots). Each year only wheat grain and straw were kept from each continuous wheat plot on Section 1 (19 plots) and from plots where wheat followed potatoes and beans (Sections 2, 4 and 7, 1968-1978). Potato tubers and bean grain and straw samples were also kept. Dyke et al (1983) summarises plant nutrients in crops grown between 1968-1978. All samples from 1970-75 were analysed for %N, P, K, Ca, Mg and Na. Samples from 1976-78 were analysed for %N only.

Thorne et al (1988) measured crop dry matter yield and %N, %P and %K from anthesis to maturity, from 1969-1984 on selected plots on Broadbalk: plots 07, 08, 15, 16, 17, 18, 21 and 22. Data was from first and second wheats in rotation with potatoes and beans. They also measured many other plant properties, including LAI, grain dry weight, number of ears, number of grains per ear, and total above-ground dry weight. Harvest index, date of anthesis and date of senescence were calculated.

From 1979-1985 %N was measured in grain and straw from the continuous wheat (Section 1) and the first wheat crop of the rotation, and in the potato tubers. From 1986-1995 %P, K, Ca, Mg and Na were also measured.

From 1996 %S was also measured (except in 2002). Nutrients were also measured in more continuous wheat sections (Sections 0 and 9 every year, and Section 8 in some years), and more of the rotational wheat sections.

Data is presented in e-RA as the following datasets:

BKWHNUTRI: Broadbalk wheat grain and straw nutrient data, 1968-2017. See grain nutrient data and straw nutrient data for details of what data is available.

BKBEANNUTRI: Broadbalk bean nutrient data, 1968-1978. See bean nutrient data for details of what data is available

BKPOTSNUTRI: Broadbalk potato tuber nutrient data, 1968-1996. See potato nutrient data for details of what data is available

BKOATNUTRI: Broadbalk oats nutrient data, 1996-2017. See oats nutrient data for details of what data is available

BKMAIZENUTRI: Broadbalk forage maize nutrient data, 1997-2017. See maize nutrient data for details of what data is available


Methodology

Nitrogen (N)

1968-1995: nitrogen content was determined by Kjeldahl digest, the digest was then analysed colorimetrically using a Technicon segmented flow analyser. If nitrate-N was expected to be high in the sample, the salicylic acid modification was used (Bremner, 1965).

1996 onwards: nitrogen content is determined by combustion analyser, based on the Dumas method. Originally a Heraeus Combustion analyser, currently a LECO combustion system is used.

Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), Sodium (Na) and Sulphur (S)

1968-late 1980s: dry ashing techniques, as described by Piper (1942) were used to produce an acid extract. The extracts were analysed for P colorimetrically on a Technicon Auto Analyser, or later equivalents (Alpkem continuous flow system / Skalar SanPlus segmented flow system), using the modified Murphy & Riley (1962) molybdenum blue method developed from Fogg & Wilkinson (1958). K, Ca, Mg and Na were determined using automated atomic absorption methods. The SP90 atomic absorption flame photometer was used to analyse Ca, Mg and Na; K was analysed by the EEL flame photometer until 1973, K was then analysed with Ca, Mg and Na by the SP90. S was not routinely measured until 1996.

1980s onwards: since the late 1980s the open tube nitric-perchloric digestion (Zarcinas, et al, 1987) has been used to produce an acid extract. P, K, Ca, Mg and Na have been determined by ICP-OES (Inductively coupled plasma-optical emission Spectrometer) since 1982, and S since 1996.

Blank (control) values: Data for sodium is presented after the analysis blanks (controls) have been subtracted from the raw data. Sodium blank values tend to be relatively large, and can be greater than the raw data. If subtracting the blank resulted in a negative value, this is shown as zero. Thus the sodium data should be treated with some caution. Blank (control) readings for the other nutrients are very small, relative to the treatment values, and have not been subtracted.

  • Bremner, J. M. (1965). Total nitrogen. In Methods of Soil Analysis. Part 2 (ed. C. A. Black), pp. 1149-1178. Madison: American Society of Agronomy.
  • Fogg, D.N. and Wilkinson, N.T. (1958). The colorimetric determination of phosphorus. Analyst, London, 83:406-414.
  • Piper, C.S. (1942) Soil and plant analysis. The University of Adelaide, Adelaide, Australia.
  • Zarcinas, B.A., Cartwright, B., Spouncer, L.R., 1987. Nitric acid digestion and multi-element analysis of plant material by inductively coupled plasma spectrometry. Communications in Soil Science and Plant Analysis 18, 131-146.
Galium tricornutum Section 8 Broadbalk
ICP-OES

Non-herbicide plot section 8 Broadbalkp
Nitric/perchloric acid digestion

Broadbalk elevated view
LECO combustion analyser

Galium tricornutum Section 8 Broadbalk
Ripe wheat

Non-herbicide plot section 8 Broadbalkp
Broadbalk grain 1945

Broadbalk elevated view
Rothamsted sample archive

Micro-nutrients

Selenium (Se)

See Fan et al (2008) in Key References below, for details of changes in Se concentration in wheat grain and soil between 1843 and 2000, in plots 3, 7, 9, 10, 14, 15 and 22.

Copper (Cu), Zinc (Zn) and Iron (Fe)

See Fan et al (2008) in Key References below, for details of changes in concentration of Cu, Zn and Fe between 1843 and 2000 in plots 3, 7, 9, 10, 14, 15 and 22.

Further information and acknowledgements

For analytical techniques used prior to 1968 see Johnston (1969) in Key References below.

For information on current analytical methods used for the Rothamsted Long-term experiments, please contact the Rothamsted Research Analytical Chemistry Unit - Harpenden laboratory,

With thanks to Andy Macdonald, Paul Poulton, Steve Freeman, Ruth Skilton and Wendy Gregory for help with compiling the information, images and text.

Galium tricornutum Section 8 Broadbalk
Wheat straw

Non-herbicide plot section 8 Broadbalkp
Wheat grain

Broadbalk elevated view
Rothamsted sample archive

Key References

2016

  • Johnston, A. E. , Poulton, P. R. , Goulding, K. W. T. , Macdonald, A. J. and Glendining, M. J.(2016) "Potassium management in soils and crops: A review", Proceedings 792, 52pp

2008

  • Fan, M.-S. , Zhao, F.-J. , Fairweather-Tait, S. J. , Poulton, P. R. , Dunham, S. J. and Mcgrath, S. P.(2008) "Evidence of decreasing mineral density in wheat grain over the last 160 years", Journal of Trace Elements in Medicine and Biology, 22, 315-324
    DOI: 10.1016/j.jtemb.2008.07.002
  • Fan, M. S. , Zhao, F. J. , Poulton, P. R. and Mcgrath, S. P.(2008) "Historical changes in the concentrations of selenium in soil and wheat grain from the Broadbalk experiment over the last 160 years", Science of the Total Environment, 389, 532-538
    DOI: 10.1016/j.scitotenv.2007.08.024

1988

  • Thorne, G. N. , Darby, R. J. , Day, W. , Lane, P. W. , Welbank, P. J. and Widdowson, F. V.(1988) "Variation between years in growth and nutrient uptake after anthesis of winter wheat on Broadbalk field at Rothamsted, 1969-84", Journal of Agricultural Science, 110, 543-559
    DOI: 10.1017/S0021859600082125

1983

  • Dyke, G. V. , George, B. J. , Johnston, A. E. , Poulton, P. R. and Todd, A. D.(1983) "The Broadbalk wheat experiment 1968-78: yields and plant nutrients in crops grown continuously and in rotation", Rothamsted Experimental Station Report for 1982 , Part 2 , 5-44
    Get from eRAdoc: ResReport1982p2-5-44

1969

1953

  • Chambers, W. E.(1953) "Nutrient Composition of the Produce of the Broadbalk Continuous Wheat Experiment .1. Changes over 70 Years", Journal of Agricultural Science, 43, 473-478
  • Chambers, W. E.(1953) "Nutrient Composition of the Produce of the Broadbalk Continuous Wheat Experiment .2. Changes Occurring During One Seasons Growth", Journal of Agricultural Science, 43, 479-484

1884

  • Lawes, J. B. and Gilbert, J. H.(1884) "On the composition of the ash of wheat-grain and wheat-straw, grown at Rothamsted in different seasons and by different manures", Journal of the Chemical Society, 45, 305-407 (Series 1/65)

Information about the wheat root and stem diseases assessed (take-all, eyespot, sharp eyespot and brown foot rot)

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Broadbalk Diseases

The following wheat root and stem diseases have been assessed on selected plots regularly since the introduction of rotations in 1968:

  • Take-all Gaeumannomyces graminis (Sacc) Arx & Oliver var.tritici
  • Eyespot Oculimacula acuformis and Oculimacula yallundae
  • Sharp eyespot Rhizoctonia cerealis
  • Brown foot rot Fusarium spp.

The take-all fungus infects winter wheat roots in the autumn causing black necrotic lesions on the roots. Early infections can lead to uneven growth in the spring and occasionally plant death. If severe infection occurs in June/early July above ground symptons often show as patches of premature ripening plants with reduced yields and grain quality. Comparisons of yields and of differences in amounts of take-all between continuous wheat on Broadbalk and wheat in other fields growing shorter sequences of cereals culminated in the development of the hypothesis of 'take-all decline'. This phenomenon is now widely recognised and has been shown to occur in all the susceptible cereals.

Galium tricornutum Section 8 Broadbalk
Large take-all patches on wheat

Non-herbicide plot section 8 Broadbalkp
Severe take-all on wheat

Eyespot was first identified in the UK in 1935 on Broadbalk. It is common on intensively cultivated cereals in heavy soils and is favoured by long wet and cold periods in winter and spring. The fungus can survive on infected stubble and in the soil for 2-4 years. Early symptoms are difficult to assess and can range from a brown smudge to a typical eye shaped lesion. Careful removal of the outer leaf sheath can reveal a small black dot, the penetrating stroma. It penetrates the leaf sheath eventually infecting the stem. Severe infection softens the stem, often showing as white heads and can lead to lodging of the crop as it matures.

Galium tricornutum Section 8 Broadbalk
Eyespot lesions on wheat

Non-herbicide plot section 8 Broadbalkp
Lodging of wheat caused by eyespot

Broadbalk elevated view
Severe eyespot on straw

Sharp eyespot causes numerous stem and stem base lesions. The fungus overwinters primarily as mycellium on infected stubble but has a large host range which can also act as a source of inoculum. As a result, the fungus is not easily controlled by rotation. Early symptoms show as well defined lesions on the outer leaf sheaths and frequently have interveinal tissue shredding within the lesion. Infection can occur at any time during the growing season. Late infections often remain on the leaf sheaths but early infections can penetrate the straw often causing multiple lesions that can be observed as far up the stem as the 4th node. Severe infection can cause white heads and make the straw brittle. The disease is favoured by cold and dry conditions and is less prevalent in intensively cultivated cereals.

Galium tricornutum Section 8 Broadbalk
Sharp eyespot lesions with interveinal tissue shredding

(Galium tricornutum) in Broadbalk

Broadbalk elevated view
Sharp eyespot on straw extending ouver several nodes

Brown foot rot is caused by Fusarium spp. and is both soil and seed-borne. Infection often begins at the base of the leaf sheath and spreads up the leaf. The fungus continues to spread eventually reaching the nodes and straw causing two distinct symptoms. An overall general browning, mainly attributed to Fusarium culmorum, and streaky brown lesions caused by Microdochium nivale. Severe Fusarium infection can result in whiteheads and occasionally lodging of the crop.

Galium tricornutum Section 8 Broadbalk
Brown foot rot lesions caused by Microdochium nivale

Broadbalk elevated view
Severe brown foot rot caused by Fusarium culmorun

Measurements

Take-all, eyespot, sharp eyespot and brown foot rot have been routinely assessed on Broadbalk on Sections 9 and the 1st, 2nd and 3rd wheats of the rotational sections since 1968. Several plots were assessed each year and from 1985 mainly plots 7 (N2PKMg), 10 (N2), 11 (N2P), 13 (N2PK), 15 (N5PKMg) and 21 (FYMN2). Disease assessments were generally carried out in late June/early July, at growth stage 69-77. Data in e-RA is currently available from 1968 - 2009, and 2016.

No disease assessments were done from 1982-1984. This was a transition period during which the rotation period changed from 3 to 5 years.

The percentage of plants with slight, moderate and severe take-all infection is assessed as follows: 0 = no infection (healthy); 1 = < 25% of the root system infected (slight take-all); 2 = 25-75% infected (moderate take-all); 3 = > 75% roots infected (severe take-all). A take-all rating (TAR) is determined (Gutteridge et al., 2003). It is calculated as follows: (1x % plants with slight infection) + (2 x % plants with moderate infection) + (3 x % plants with severe infection). The TAR is a measure of take-all intensity with a range from 0 (no take-all) to 300 (severe infection on all plants).

The severity of infection by eyespot is assessed as described by Scott & Hollins (1974). Plants with slight eyespot have small lesions occupying less than half of the circumference of the straw. Plants with moderate eyespot have lesions occupying more than half of the circumference of the straw. In plants with severe eyespot the straw is completely girdled by lesions and/or tissue softened.

Symptoms of sharp eyespot are often very superficial and a distinction is made only between symptoms that are slight, small lesions occupying less than half of the circumference of the straw or severe where lesions occupy more than half of the circumference of the straw and usually extend over more than one internode (Goulds & Polley, 1990).

Brown foot rot is classified as slight or severe (Goulds & Polley, 1990). Plants with slight brown foot rot have either a general light browning occupying most of the circumference of the straw (typically caused by Fusarium culmorum) or fewer than 5 dark brown-black narrow streaks c.1mm wide (typically caused by F. nivale). Severe symptoms are defined as a general dark brown discoloration of the straw usually extending over more than one internode (F. culmorum) or more than 5 brown-black streaks greater than 1mm wide (F. nivale).

With thanks to Richard Gutteridge for providing the photographs and helping to compile the text.

For more information, refer to the Rothamsted Guide to the Classical Experiments 2018 page 17

Key References

2003

  • Gutteridge, R. J. , Bateman, G. L. and Todd, A. D.(2003) "Variation in the effects of take-all disease on grain yield and quality of winter cereals in field experiments", Pest Management Science, 59, 215-224
    DOI: 10.1002/ps.574

1996

  • Gutteridge, R. J. , Jenkyn, J. F. and Poulton, P. R.(1996) "Occurrence of severe take-all in winter wheat after many years of growing spring barley, and effects of soil phosphate", Aspects of Applied Biology, 47, 453-458

1995

  • Bateman, G. L. and Coskun, H.(1995) "Populations of Fusarium Spp in Soil Growing Continuous Winter- Wheat, and Effects of Long-Term Application of Fertilizers and of Straw Incorporation", Mycological Research, 99, 1391-1394
    DOI: 10.1016/S0953-7562(09)81227-6

1990

  • Goulds, A. and Polley, R. W.(1990) "Assessment of eyespot and other stem base diseases of winter wheat and winter barley", Mycological Research, 94, 819-822
    DOI: 10.1016/S0953-7562(09)81384-1

1974

  • Scott, P. R. and Hollins, T. W.(1974) "Effects of eyespot on yield of winter wheat", Annals of Applied Biology, 78, 269-278

1969

1968

  • Snyder, W. C. and Nash, S. M.(1968) "Relative incidence of Fusarium pathogens in cereals in rotation plots at Rothamsted", Transactions of the British Mycological Society, 51, 417-425
    DOI: 10.1016/S0007-1536(68)80009-9

Information about earthworm measurements on Broadbalk

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Broadbalk Earthworm measurements

Earthworm populations were assessed on Broadbalk in 1920-21, 1979, 2014 and 2015. Details are given below. The results are not directly comparable, as different methods were used for each assessment.

Feb 1920-Jan 1921 (Morris, 1922)

Morris recorded insect and other invertebrate fauna, including earthworms, on Broadbalk between February 1920 and January 1921. Samples were taken from two plots: FYM (Plot 2), receiving 35t/ha FYM annually since 1843 and the unfertilized plot (Plot 3) - no fertiliser or manure since 1843.

Samples were taken from the Western end of the plots, using a metal box 23x23cm with a total of five depths: 0-2.5cm, 2.5-7.6cm, 7.6-12.7cm, 12.7-17.8cm and 17.8-23cm. 23 samples were taken from each plot, approximately every 12 days, between Februrary 1920 and January 1921. Soil was not sampled on rainy days, due to the difficulty of examining wet soil. FYM was applied to Plot 2 and the Plots were ploughed on October 13th 1920. The plough depth was around 14-16cm, i.e. the fourth layer measured.

Earthworms were defined as belonging to the sub-order Terricolae in the order Oligochaeta, including Lumbricus sp.

Results:

Earthworms were recorded in all 12 months, and in all five depths (0-23cm)
Earthworms were most common in the second soil layer sampled (2.5-7.6cm deep)
Over twice as many earthworms were present in the plot given FYM since 1843 as in the plot never given fertiliser or manure
A total of 2.50 million earthworms/hectare (250/m2) were recorded in the FYM plot from 23 samples
A total of 1.13 million earthworms/hectare (113/m2) were recorded in the unfertilized plot from 23 samples
Earthworms were thought to occur at deeper depths than 23cm in both plots

September 1979 (Edwards & Lofty, 1982)

Edwards & Lofty measured earthworm numbers and total biomass in various Broadbalk plots growing continuous winter wheat, to investigate the effects of nitrogen (N) fertilizers. Earthworm populations were sampled in September 1979 by pouring dilute formalin on to 16 0.25 m 2 quadrats and collecting the worms that were brought to the surface.

Results:

All species of earthworm were more numerous in plots treated with organic fertilizers
There was a strong positive correlation between the amounts of inorganic N fertilizer applied and populations of earthworms
Plots receiving both inorganic and organic N had the largest populations of earthworms

See September 1979 earthworm data (pdf) for summary of the Edwards & Lofty (1982) data from Broadbalk.

Spring 2014 (Sizmur et al, 2017)

Earthworm surveys were carried out on four parts of Broadbalk in spring 2014, receiving the following treatments each year:

  • NPK: 144kgN/ha plus PK since 1852. Straw removed (Plot 8, Section 1)
  • NPK+straw: 144kgN/ha plus PK since 1852. Since 1986 straw incorporated each year (Plot 8, Section 0)
  • FYM: 35t/ha FYM since 1885, plus fertilizer N since 1968 (96 kgN/ha 1968-2004, 144 kgN/ha since 2005). Straw removed (Plot 2.1, Section 1)
  • FYM+straw: 35t/ha FYM since 1885, plus fertilizer N since 1968 (96 kgN/ha 1968-2004, 144 kgN/ha since 2005). Since 1986 straw incorporated each year (Plot 2.1, Section 0)
  • A 1m x 14m area on the northern edge of each plot was used, divided into four equal sub-plots. Two earthworm surveys were carried out in each sub-plot, a total of 8 surveys per treatment.

    Earthworm surveys were conducted by excavating a 20 x 20 x 20cm cube of soil, which was brought back to the laboratory and sorted to find and identify all the earthworms. Deep burrowing (anecic) earthworms were extracted by pouring a 5 L aqueous solution containing 6g/l of mustard flour (see Sizmur et al 2017 for full details).

    Results:

    Plots given FYM contained a significantly greater biomass and number of earthworms than the plots never given FYM
    Total earthworm biomass was 109 g/m2 in plots given FYM, compared to 6 g/m2 in plots never given FYM
    Total earthworm numbers were 400/m2 in plots given FYM, compared to 70/m2 in plots never given FYM
    28 years of straw incorporation had no significant effect on the earthworm populations
    There was no significant interaction between straw and FYM on earthworm abundance or biomass

    Broadbalk total earthworm biomass and abundance, spring 2014 (Sizmur et al, 2017)

    Measurement
    NPK
    NPK+Straw
    FYM
    FYM+straw
    Total biomass (g/m2)
    Total abundance (numbers/m2)
    7.4 +/-0.9
    81.3 +/-16.5
    4.7 +/-1.4
    59.4 +/-12.9
    103.2 +/-24.6
    471.9 +/-80.1
    114.6 +/-17.8
    328.1 +/-50.1

     

    +/- standard errors of the mean, based on four replicate sub-plots and two surveys per sub-plot.

    For further details of the different earthworm species recorded in the survey, see Spring 2014 biomass (pdf) and Spring 2014 abundance (pdf).

    Earthworm biomass and abundance were also measured in spring 2014 on the long-term straw incorporation experiment at Rothamsted, which had four rates of cereal straw incorporated annually for 28 years. The highest rate of straw (20t/ha) resulted in significantly greater earthworm abundance and biomass. See Sizmur et al (2017) for more details.

    Autumn 2015 (Stroud et al, 2016)

    Stroud et al carried out midden counts on two Broadbalk plots in September 2015, to assess populations of anecic, deep burrowing Lumbricus terrestris earthworms. The plots received the following treatments each year:

  • NPK: 144kgN/ha plus PK since 1852. Straw removed (Plot 8, Section 1)
  • FYM+N: 35t/ha FYM since 1885, plus fertilizer N since 1968 (96 kgN/ha 1968-2004, 144 kgN/ha since 2005). Straw removed (Plot 2.1, Section 1)
  • Midden assays (5 m2 per plot) were carried out with 1 m2 mustard validation assays. 1.5l of mustard solution containing 20g mustard powder in water were poured within a 0.25 m2 square quadrat in a random location within the plot. Earthworms (L. terrestris) were collected for species analysis and then released. The results are not directly comparable with earlier assessments, as different methods were used.

    Results:

    The plot ammended with FYM + N contained 0.3 middens per m2
    The plot ammended with NPK contained 0.13 middens per m2

    Middens counts were also carried out on three other arable sites at Rothamsted and Woburn, with and without organic ammendments (straw, biosolids, and organic wastes). Organic matter applications enhanced L. terrestris populations, however these populations were very low, never exceeding 4.6 per m2. See Stroud et al (2016) for more details.

    Key References

    2019

    • Sizmur, T. , Martin, E. , Wagner, K. , Parmentier, E. , Watts, C. W. and Whitmore, A. P.(2019) "Corrigendum to Milled cereal straw accelerates earthworm (Lumbricus terrestris) growth more than selected organic amendments [Appl. Soil Ecol. 113 (2017) 116177]", Applied Soil Ecology, 142, 199-200
      DOI: 10.1016/j.apsoil.2018.10.013

    2018

    2017

    • Sizmur, T. , Martin, E. , Wagner, K. , Parmentier, E. , Watts, C. and Whitmore, A. P.(2017) "Milled cereal straw accelerates earthworm (Lumbricus terrestris) growth more than selected organic amendments", Applied Soil Ecology, 113, 166-177
      DOI: 10.1016/j.apsoil.2016.12.006

    2016

    • Stroud, J. L. , Irons, D. E. , Watts, C. W. , White, R. P. , Mcgrath, S. P. and Whitmore, A. P.(2016) "Population collapse of Lumbricus terrestris in conventional arable cultivations and response to straw applications", Applied Soil Ecology, 108, 72-75
      DOI: 10.1016/j.apsoil.2016.08.002

    1982

    • Edwards, C. A. and Lofty, J. R.(1982) "Nitrogenous fertilizers and earthworm populations in agricultural soils", Soil Biology and Biochemistry, 14, 515-521
      DOI: 10.1016/0038-0717(82)90112-2

    1922

    Description of what grain quality data is available (TGWs, Hagberg falling number ,Hectolitre weights, grain size categories), and analytical methods used

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    Broadbalk grain quality data

    The Broadbalk experiment was started in 1843 to investigate the relative importance of different fertilizers and manures on the grain yield of winter wheat. Since 1974, the wheat grain has been regularly analysed for standard grain quality characteristics.

    Data available

    BKGR_QUALITY: Broadbalk wheat grain quality, 1974-2018, on selected plots, containing:

    • Thousand grain weight (TGW) since 1974
    • Hagberg Falling Number (HFN) since 1999
    • Hectolitre weight (HLWT) since 1999
    • Grain size classes (% grain between 1-3.5mm) since 1999
    • Wheat variety
    • Previous crop (for the Sections of Broadbalk in rotation)
    • Number of years since last non-wheat crop, which indicates when the section was last fallowed, for the Sections in continuous wheat

    See grain quality data available for details of what measurements are available, and from which plots and sections of Broadbalk. Data is available for Section 1 (continuous wheat) and the Section in the 1st wheat of the rotation every year, with other sections in other years.

    Other data:

    • Wheat Hectolitre weight (HLWT) derived from Bushel weights, 1844 - 1955.

    BKOATS : Broadbalk oats grain quality, 1996-2018, for all plots each year, containing:

    • Thousand grain weight (TGW) since 1996
    • Hectolitre weight (HLWT) since 1999
    • Grain size classes (% grain between 1-3.5mm and % 1-2.2mm) 1999-2004

    Methodology and background information

    TGWs: The thousand grain weight is the weight in grams of 1000 cereal kernels. It is determined using an automatic grain counter. After counting, the grain is dried overnight at 105 degrees C. TWGs are useful for determining the evenness of grain size (by comparing several TGWs). The TGW is also important when calculating the drilling rate for sowing cereals.

    HFN: The Hagberg Falling Number is a recognised international test used by millers to assess the level of germination/sprouting within a batch of wheat intended for bread making. Developed in the 1950s, the Hagberg apparatus measures the time taken for a plunger to fall through a standardised hot slurry of milled wheat flour. As wheat begins to germinate it produces the enzyme alpha-amylase, which reduces the bread making potential of the wheat, and reduces the HFN. A HFN of 300 seconds or more is generally accepted as the cut-off point for bread making. A low HFN would reduce the value of the crop and could mean that the grain could only be sold for animal feed. The process includes 60 seconds of mixing, when the plunger is automatically rapidly lifted up and down by the mechanism. At 60 seconds, the plunger is released at its highest point so it can fall through the mixture. Thus the minimum possible reading is 60. THe HFN is determined on fresh grain. From 2016 the HFN is measured with a Perten Instruments FN1000, and is the mean of two readings.

    HFNs in 2007 and 2010 were very low. This is probably because it was very wet around harvest, and the grain had started to sprout before it could be harvested.

    HLWT: The hectolitre weight is the weight in kilograms of 100 litres of grain. It is calculated from specific weight of grain. Specific weight of grain is measured using a chondrometer and is equal to the weight in grams of a one litre volume of grain. HLWT is calculated from specific weight (grams per litre) as g/l x 0.10033 + 0.42119 = kg/hl. HLWT is determined using fresh grain, and the sample is weighed fresh.

    HLWT is used to quantify the size of grains and the proportion of broken or thin, shrivelled grain. Millers use HLW to help determine the quality of grain and its potential end use as bread, biscuit or pasta flours.

    Size classes: Size classes of grain are determined using a Winnower sieve, using fresh grain. The % of grain between 1-3.5mm is recorded. This is divided into the % between 1-2.25mm and the % between 2.25 and 3.5mm. The proportion of grain between 2.25 and 3.5mm is what would normally be used by millers for flour. This is calculated by subtracting the proportion of grain between 1-2.25mm from the proportion of grain between 1-3.5mm. A weighed sample is passed through slotted sieves. The same sample is sieved twice, using different sized sieves in turn. Screenings are undersized, broken or shrivelled grain between 1 and 2.25mm. Admixture comprises impurities, such as straw, chaff, weed seeds and earth, which must be removed before milling marketable flour. Screenings and admixture represent a loss to the miller, so a maximum of 2% is normally allowed.

    In 2014, a few of the plots had a measurable amount of grain greater than 3.5mm. If you would like this data, please contact the e-RA Curators.

    Galium tricornutum Section 8 Broadbalk
    wheat grain

    Non-herbicide plot section 8 Broadbalkp
    Grain counter

    Broadbalk elevated view
    Hagberg falling number apparatus

    Galium tricornutum Section 8 Broadbalk
    Winnower sieve

    Non-herbicide plot section 8 Broadbalkp
    Half-litre chondrometer

    Broadbalk elevated view
    Litre chondrometer

    Early studies

    Hectolitre weights (HLWT), derived from bushel weights, are available for all plots and sections on Broadbalk from 1844 - 1955, for dressed grain measured at threshing. Bushel weight is the weight of a bushel of grain (one bushel = 36.369 litres). Bushel weights (measured in lbs/bushel) have been converted to HLWT (kg/hl), (one lb = 0.4536 kg). From 1844 to 1901 Broadbalk was harvested by hand, and then by binder until 1956. The sheaves were 'stooked' on the plot, then carted to a barn and stored until threshing in winter, when bushel weight was determined by weighing a bushel measure filled with grain (see Atkinson et al, 2008 in Key References below). The measurement of bushel weights was discontinued in 1955 (Johnston and Garner, 1969). If you would like access to this early data, please contact the e-RA Curators.

    Related studies

    Godfrey et al (2010) assessed wheat grain protein compostion and dough properties on selected Broadbalk plots, 2005-2007. See Key References below.

    Atkinson et al (2008) looked at the relationship between grain specific weight/hectolitre weight and the winter North Atlantic Oscillation for plot 22 (FYM) Section 1 of Broadbalk, from 1844-2001. Grain specific weight was derived from the bushel weight of dressed grain, 1844-1955 (see Early studies, above). Specific weight was measured in archived samples of clean grain from 1956-2001. For further details, see Key References below.

    Gutteridge et al (2003) investigated the relationship between take-all disease and wheat grain quality (TGW, HLWT, HFN and grain size) at other field sites at Rothamsted. For further details, see Key References below.

    Grain protein content is an important property, determining suitability for breadmaking. A minimum protein content for breadmaking wheat in the UK is typically 13% dry basis. Protein % can be calculated as %N x 5.7. See Broadbalk Crop Nutrient Content for details of Broadbalk grain %N.

    For more details, contact the e-RA Curators.

    Acknowledgements

    With thanks to Steve Freeman, Chris Hall, Andy Macdonald and Paul Poulton for help with compiling the information, images and text.

    Key References

    2020

    • Ben Mariem, S. , Gamez, A. L. , Larraya, L. , Fuertes-Mendizabal, T. , Canameras, N. , Araus, J. L. , Mcgrath, S. P. , Hawkesford, M. J. , Murua, C. G. , Gaudeul, M. , Medina, L. , Paton, A. , Cattivelli, L. , Fangmeier, A. , Bunce, J. , Tausz-Posch, S. , Macdonald, A. J. and Aranjuelo, I.(2020) "Assessing the evolution of wheat grain traits during the last 166 years using archived samples", Scientific Reports, 10
      DOI: 10.1038/s41598-020-78504-x
    • Lovegrove, A. , Pellny, T. K. , Hassall, K. L. , Plummer, A. , Wood, A. , Bellisai, A. , Przewieslik-Allen, A. , Burridge, A. J. , Ward, J. L. and Shewry, P. R.(2020) "Historical changes in the contents and compositions of fibre components and polar metabolites in white wheat flour", Scientific Reports, 10, 5920
      DOI: 10.1038/s41598-020-62777-3

    2010

    • Godfrey, D. , Hawkesford, M. J. , Powers, S. J. , Millar, S. and Shewry, P. R.(2010) "Effects of Crop Nutrition on Wheat Grain Composition and End Use Quality", Journal of Agricultural and Food Chemistry, 58, 3012-3021
      DOI: 10.1021/jf9040645

    2008

    • Atkinson, M. D. , Kettlewell, P. S. , Poulton, P. R. and Hollins, P. D.(2008) "Grain quality in the Broadbalk Wheat Experiment and the winter North Atlantic Oscillation", Journal of Agricultural Science, 146, 541-549
      DOI: 10.1017/s0021859608007958

    2003

    • Gutteridge, R. J. , Bateman, G. L. and Todd, A. D.(2003) "Variation in the effects of take-all disease on grain yield and quality of winter cereals in field experiments", Pest Management Science, 59, 215-224
      DOI: 10.1002/ps.574

    Description of potatoes, oats, beans and forage maize crops grown on Broadbalk, and the management of the fallow

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    Broadbalk Yields - Other Crops and Fallow

    Broadbalk Description of other crop yield data
    Other arable crops and fallow have been included in the rotational sections of Broadbalk since 1968 (see Cropping plan for details). See below for further details of fertilizer applications and other treatments, including to the fallow sections . Yield data is available from the following datasets:

    BKBEANS Spring bean grain and straw yields 1968 -1978; Winter bean grain and straw yields 2018 -
    BKPOTATO Potato tuber yields 1968 -1996
    BKMAIZE Forage maize whole crop yields 1997 - 2017
    BKOATS Winter oat grain and straw yields 1996 - current year


    Spring field beans (Vicia faba) were grown on the rotational sections of Broadbalk between 1968 and 1978, as part of the potato > beans > wheat rotation on sections 2, 4 and 7. For full details of the cropping sequence see Cropping on Broadbalk. The varieties were Maris Bead (1968-74), Minor (1975) and Minden (1976-78). The beans were sown in March and generally harvested in September. The crops received the same inorganic fertilizer (including N) and FYM applications as the wheat crops. The N is applied in the seedbed. Grain and straw yields at 85% DM, thousand grain weights, variety, sowing and harvest dates are available from dataset BKBEANS.


    Winter field beans (Vicia faba) replaced forage maize on the rotational sections of Broadbalk from 2018 onwards, and the rotation was changed to wheat/wheat/oats/wheat/beans. For full details of the cropping sequence see Cropping on Broadbalk. The beans are sown in the autumn and harvested in August/September. No fertilizer N or FYM is applied; P, K and Mg are as for the wheat crops. Grain and straw yields at 85% DM and thousand grain weights are available, along with variety, sowing and harvest dates from dataset BKBEANS.


    Potato (Solanum tuberosum) was grown on the rotational sections of Broadbalk between 1968 and 1996, as part of the potato > beans > wheat rotation of Sections 2, 4 and 7 (1968-78) and then as part of the potato > wheat > wheat > wheat > fallow rotation of Sections 2-5 and 7 (1979-96). For full details of the cropping sequence see Cropping on Broadbalk. The varieties grown were Majestic (1968-69), King Edward (1970-75), Pentland Crown (1976-93), Estima (1994-96). The crops received the same inorganic fertilizer and FYM applications as the wheat crops. Fertilizer N was applied in the spring, before rotary cultivation to prepare the seedbed. Chitted potato seed was generally planted in April and harvested in September; please apply to the e-RA Curators for a full list of dates since 1968. The potatoes were usually harvested earlier than normal to allow timely drilling of winter wheat, hence the yields are lower than might be expected.

    Data available includes total tuber yield, tuber DM content and % ware (tubers that do not pass through a 3.81cm ‘riddle’ or grader). ‘Ware’ potatoes are those grown for human consumption, which need to be a minimum size, generally over 40mm. Potatoes are graded according to size, using a potato riddler.


    Forage maize (Zea mays) was grown as a whole crop, for silage. It has been grown in the rotational sections 2-5 and 7, 1997-2017, as part of the wheat > wheat > wheat > oats > maize rotation. Maize is a C4 plant. As such, the carbon it contains has a different 13C "signature" than that in the C3 plants that have been grown previously on Broadbalk. Thus, we can distinguish maize-derived organic matter from that of organic matter already in the soil. For full details of the cropping sequence see Cropping on Broadbalk. The variety Hudson was grown 1997-2014, and the variety Severus 2015-2017. Forage maize is generally sown in May and harvested in September; please apply to the e-RA Curators for a full list of dates since 1997. Maize receives the usual inorganic fertilizer and FYM applications, the same as wheat. In 2013, forage maize yields may have been reduced, due to the accidental application of herbicide to the crop in June/July 2013. The last crop of forage maize was grown in 2017. A new rotation including winter beans instead of maize was started in 2018.


    Winter oats (Avena sativa) has been grown on the rotational sections 2-5 and 7 since 1996, as part of the wheat/wheat/wheat/oats/maize rotation. For full details of the cropping sequence see Cropping on Broadbalk. The varieties grown were Image (1996-2000), Revisor (2001) and Gerald (2002-onwards). Revisor, a spring variety, was sown in 2001 due to poor autumn weather preventing a winter variety from being sown. Oats are generally sown in October and harvested in August; please apply to the e-RA Curators for a full list of dates since 1996. No fertilizer N or FYM was applied to the oats crops harvested 1996-2017; K and Mg were applied as usual. Thus, on plots were P and K is not limiting, any differences in yield between treatments were due to residues of inorganic N from previous applications or from differing amounts of N being mineralised from the soil organic matter.

    Since 2018 the rotation was changed to wheat/wheat/oats/wheat/beans, and N is now applied to the oats at 1/2 the usual rate as a single application in mid-April (i.e. 24, 48, 72, 96, 120 and 144 kgN/ha). FYM is applied at the usual rate to the sections growing oats.


    Bare fallow, 1968-1995 was included as part of the three year rotation (wheat > wheat > fallow) on sections 3, 5 and 6 from 1968-1979, and as part of the three or five year rotation on sections 2-5 and 7 from 1979-1995. The fallow sections received FYM and castor meal, and the autumn inorganic fertilizers (P, K, Na and Mg) at the same time as the cropped sections (in the autumn, before ploughing). However, no inorganic N was applied to the fallow sections. The fallow sections were cultivated several times, to remove weeds, and herbicides were also applied. The continous wheat sections (0, 1, 6, 8 and 9) are occasionally bare fallowed to control perennial weeds, most commonly Section 8 (which does not receive herbicides).


    Bare fallow, 1926-1967. Regular bare fallowing was introduced in 1926, with cultivations to kill the weeds. No FYM, castor bean meal or inorganic fertilizer was applied to the fallow sections. This decreased the soil organic matter content, especially on the plots usually given FYM. No herbicides were applied to the fallow sections.

    For more information, refer to the Rothamsted Guide to the Classical Experiments 2018 pages 7-12.

    Details of which soil chemical properties have been measured, analytical methods used and soil sampling methods

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    Broadbalk soil chemical properties background information

    The Broadbalk wheat experiment, established in the autumn of 1843, has been cultivated since at least 1623, and probably much earlier (Avery & Bullock, 1969). Soil chemical properties have been measured at regular intervals since 1865.

    Soil pH: The plough layer (0-23 m) is limed when necessary to maintain a minimum soil pH of 7.0 - 7.5. Broadbalk was first limed regularly from 1955-1967, with plots given the larger inputs of ammonium fertilizers receiving more lime than the controls. Liming stopped from 1968-1975, but began again in 1976-1992, with 3 or 4 sections being limed each year. From 2007 onward selected plots have been limed every 5-6 years based on soil pH measurements to maintain top-soil pH around 7.0-7.5. Selected plots were limed in autumn 2018.

    Data available

    Soil chemical properties have been measured at regular intervals on Broadbalk since 1865, in topsoils (0-23cm) and subsoils. See soil measurements 1843-1944 and soil measurements 1966-2017 for details of what data is available. Not all plots, sections or soil depths have been measured every year. The following soil chemical properties have been measured:

    • %N : total soil Nitrogen %
    • %SOC : soil organic Carbon %
    • Olsen P : plant-available phosphorus, by extraction with a solution of 0.5M NaHCO3, buffered at pH 8.5
    • pH : soil pH in water (1:2.5 soil : solution)
    • Exchangeable cations : exchangeable Ca, K, Mg and Na by extraction with 1M ammonium acetate solution
    • % inorganic carbon (CaCO3-C) : by calcimetry
    • soil weights : see soil physical properties for details

    Soil Sampling

    Broadbalk soil has been sampled on many occasions over the years. However, because the method of sampling has changed and the experiment has been divided, first into two halves, then into five sections and finally into 10 sections, it is not always advisable to directly compare one sampling with another without careful thought. This table shows, where possible, how samples taken over time relate to each other. Selected plots and depths have been sampled on other occasions; most samples still exist in the Sample Archive.

    Since 1992 a systemic sampling plan has been adopted. In 1992, 1997, 2005, 2010 and 2015 all five continuous wheat sections were sampled (0, 1, 6, 8 and 9). In the intervening years the remaining sections in rotation were sampled, one per year, so that all sections were sampled every five years. All sections were sampled in 2000 prior to treatment changes being introduced. See table for full details.

    In autumn 2004 it was apparent that parts of the field had been ploughed slightly deeper than 23cm as sub-soil clay was visible in random patches across the field. Thus in 2005 and 2006 all plots were resampled to create a new baseline, if necessary, for soil chemical properties. The sections were then sampled systematically from 2008 onwards.

    In 2000-2004 archived soil samples from selected plots sampled in 1865, 1881, 1893, 1914, 1936 and 1944 were re-analysed for soil pH, Olsen-P, exchangeable cations, Total %N, %SOC and CaCO3-C. Values for %N and %SOC from the re-analysis of the 1865 samples were very different to the original data and the 1881 and 1893 re-analysed soils, so the original data was used.

    Data before 1926 (when the experiment was divided into sections) are given for whole plots only, from the re-analysis in 2000/2004. More recent data are available for individual plots within each section.

    1936, 1944 and 1966 data is included with later data, although the experiment was not divided into 10 sections until 1968.

    1936 data: 10-20 cores taken with a narrow auger from each of the five Old Sections were bulked within each plot. Data for Old Section I is used for current sections 0 and 1, Old Section II for current sections 2 and 3, etc. (see soil sampling plan for more details). All the data is from the re-analysis of old samples in 2001-2002.

    1944 data: four holes were taken from each of the (then) five Old Sections; holes 1 & 2 were on current Section 0, holes 3 & 4 on current Section 1 etc, so the data can confidently be allocated to the modern sections. Data is presented as the mean of the two holes for the topsoil. Subsoil data is not available for each modern section, as the samples were bulked from four-sub-samples for each of the five old sections. Data for Old Section I is used for current sections 0 and 1, Old Section II for Sections 2 and 3, etc. (see soil sampling plan for more details). The soil was re-analysed in 2003-5 from selected plots from all Sections and depths. All data is from the re-analysis except %CaCO3 which was analysed in 1944. Soil pH and Exchangeable Na were not measured in the 1944 subsoil samples.

    1966 data: Section 0 and 1 use data from Old Sections Ia and Ib respectively; Sections 2 and 3 use data from Old Section II; Sections 4 and 5 use data from Old Section III; Sections 6 & 7 use data from Old Section IV; Sections 8 and 9 use data from Old Sections Va and Vb respectively. Bulked Va and Vb samples (ie Sections 8 and 9) were used to determine %SOC (plots 2.1 and 2.2 only) and for all plots for Olsen P, %CaCO3 and Exchangeable K. There was no plot 1 in 1966, this was created in 1968. The soil was sampled in September 1966 but no day is given. It is shown as 15/09/1966 in the database.

    Data from the samplings in 2001-2004 is not included as this only covered sections 2, 4, 5 and 7 and there was a comprehensive sampling of all sections in 2000 and then in 2005/6.

    Soil Sampling Methods

    Samples between 1865 and 1914 were taken with an open-ended metal box, 9 inches (23cm) deep and usually 6 x 6 inches (15 x 15cm) across. There were between three and eight sample positions on each plot which were bulked together for each depth on each plot. In 1944 a spade was used to sample the 0-23cm layer, and the subsoil (23-46cm) was sampled with a semi-cylindrical auger.

    In 1936 and from 1966 onwards samples were taken with a semi-cylindrical auger. 10-20 cores were taken from the different soil layers for each individual plot within each section and bulked together for each plot. Small diameter cores taken by semi-cylindrical augers cannot be used to determine soil weights, but provided enough are taken the sample better represents the proportions of SOC, N, P, K etc in the soil than a few large box samples. See soil physical properties for details of soil weights.

    Samples were taken in the autumn, after the crop had been removed, but before ploughing, except for Section 3, 1996 which was sampled in March.

    Broadbalk sampling
    Soil sampling Broadbalk 1943

    Non-herbicide plot section 8 Broadbalkp
    Soil sampling Broadbalk 1943

    Broadbalk sampling
    Broadbalk ploughing in 2013

    Analysis methods for soil chemical properties

    All soil samples are air-dried and sieved <2mm. Data are given for air-dried soil (approximately 98% dry matter). When calculating total amounts in the soil (e.g. kg N ha-1 ) you may wish to convert to oven-dry soil (i.e. 100% dry matter). Broadbalk standard soil weights are given for oven-dry soil.

    For information on current analytical methods used for the Rothamsted Long-term experiments, please contact the Rothamsted Research Analytical Chemistry Unit - Harpenden laboratory,

    Total soil % nitrogen (%N)

    1865: Original soda lime analysis for total N (Johnston, 1969b, table 5.10) multiplied by a factor derived from the comparison of soda lime and LECO analysis values for 1881 and 1893 samples. Soda lime analysis by the method of Will and Varrentrapp (Watt, 1863). See Johnston (1969a, p 50) for more details.

    1881-1944: Selected samples re-analysed in 2001-4 by combustion analysis, based on the Dumas method, using a LECO combustion system. Measured on air-dried, finely ground soil (to pass a 355 micron or 44 mesh sieve).

    1966, 1987-8: Kjeldahl digest method for total N (Bremner, 1965). The digest was then analysed colorimetrically using a Technicon continuous flow analyser. Measured on air-dried soil, finely ground to pass a 0.5mm sieve.

    1992 onwards: Combustion analysis, based on the Dumas method, using a LECO combustion system. Measured on air-dried, finely ground soil (to pass a 355 micron or 44 mesh sieve).

    Soil % organic carbon (%SOC)

    1865: Derived from original soda lime analysis for total N and C:N ratios for 1893 for organic carbon (Dyer, 1902).

    1881-1944: Selected samples re-analysed in 2001-4 by combustion analysis, based on the Dumas method, using a LECO combustion system to measure total carbon. SOC determined as total C minus CaCO3-C, measured by a calcimeter (see below). Measured on air-dried, finely ground soil (to pass a 355 micron or 44 mesh sieve).

    1966: Chromic acid titration method (Walkley and Black, 1934). Correction factor of W-B x 1.3 used, which is equivalent to organic C by Tinsley or total C by combustion minus CaCO3-C. But see also Johnston (1969b, p 97). Measured on air-dried soil, ground to pass a 0.5mm sieve.

    1987-8: Dichromate digestion, modified Tinsley (Kalembasa and Jenkinson, 1973) to measure organic C. Measured on air-dried soil, finely ground to pass a 0.5mm sieve.

    1992 onwards: Combustion analysis, based on the Dumas method, using a LECO combustion system to measure total C. Measured on air-dried, finely ground soil (to pass a 355 micron or 44 mesh sieve). SOC determined by subtraction of CaCO3-C, measured by a calcimeter (see below).

    Inorganic carbon (IC) also known as calcium carbonate-C or CaCO3-C

    Soils sampled in 1865-1936 were re-analysed in 2000-4. Most of the 1944 data was from the 1944 analysis, except for a few plots (9, 18 and 19) that were analysed in 2001. IC was not measured in 1987-88, as %SOC was determined directly by Tinsley analysis. In other years IC is subtracted from total carbon to give %SOC.

    All samples up to 2012 were analysed by a calcimeter. CO2 is liberated from CaCO3 in the soil sample by treating with hydrochloric acid (HCl) in a closed system. The amount of CaCO3 is calculated by comparing the pressure produced by the sample against the pressure produced by known weights of CaCO3, using a mercury filled manometer. %CaCO3-C or %IC is derived from %CaCO3 by dividing by 8.333. Since 2014 inorganic C has been measured by an automated Skalar Primacs inorganic carbon analyser.

    Soil pH

    Soil pH in water, with a 1:2.5 soil:water suspension, mean of two readings. Soils from selected treatments sampled in 1865-1944 were re-analysed in 2000-4. Measured on air-dried soil, sieved < 2mm.

    Olsen-P (plant-available phosphorus; also known as bicarbonate soluble-P or NaHCO3-soluble P)

    Soils from selected treatments sampled in 1865-1944 were re-analysed in 2000-4. All samples were analysed by the Olsen method, in which soil is extracted with a solution of 0.5M NaHCO3, buffered at pH 8.5 (Olsen et al, 1954). The extract is then analysed by continuous segmented colorimetric flow analysis. Measured on air-dried soil, sieved < 2mm.

    See Blake et al (2000, 2003) for a discussion of the P balance on Broadbalk and changes in soil P fractions over time (Key References, below).

    Exchangeable cations - Calcium (Ca), magnesium (Mg), potassium (K) and sodium (Na)

    Selected soils sampled in 1865-1944 were re-analysed in 2000-6, and those sampled in 1966 were re-analysed in 2019. All soils were extracted with 1M ammonium acetate (NH4CH3CO2) solution, after the method of Metson (1956). The data is expressed as mg kg-1 in dry matter, with 5mg of soil in 100ml of leachate. Since 1983, the extracts have been analysed by ICP-OES (Inductively Coupled Plasma - Optical Emission Spectrometer). Measured on air-dried soil, sieved < 2mm.

    Blank (control) values: Analysis blanks were subtracted from exchangeable Na, and other cations if necessary (e.g. K in 1987).

    Samples taken in 1966 were re-analysed in 2019. The exchangeable K values differ from those published by Johnson (1969b), when a slightly different technique was used for measuring exchangeable cations, which involved swirling the samples in successive amounts of ammonium acetate and decanting off the solution once settled. In 1966 the extracts were measured with a flame photometer. Bolton (1972) reports on exchangeable Ca and Mg in Broadbalk soils from 1856-1966 for some sections, from the western (top) end of the field, but the 1966 data has not been found. It is recommended that the re-analysed data from 2019 is used for the 1966 samples.

    See Bolton (1972) for changes in exchangeable Ca and Mg, 1856-1966 and Blake et al (1999) for a study of soil K content, crop K uptake and K balance in Broadbalk (Key References, below).

    Methods References:

  • Bremner, J. M. (1965). Total nitrogen. In: Methods of Soil Analysis. Part 2 (ed. C. A. Black), pp. 1149-1178. Madison: American Society of Agronomy
  • Johnston, A. E. (1969a) "The plant nutrients in crops grown on Broadbalk", Rothamsted Experimental Station Report for 1968, Part 2, 50-62 DOI:10.23637/ERADOC-1-34916
  • Johnston, A. E. (1969b) "The soils of Broadbalk: Plant nutrients in Broadbalk soils", Rothamsted Experimental Station Report for 1968, Part 2, 93-115 DOI:10.23637/ERADOC-1-34923
  • Kalembasa, S.J and Jenkinson, D.S (1973) A comparative study of titrimetric and gravimetric methods for the determination of organic carbon in soil. Journal of the Science of Food and Agriculture 24: 1085-1090.
  • Metson, A.J. (1956). Methods of chemical analysis for soil survey samples. New Zealand Soil Bureau, Bulletin 12.
  • Olsen S.R., Cole C.V., Watanabe F.S., Dean L.A. (1954) Estimation of available phosphorus in soils by extraction with sodium bicarbonate. USDA Circular 939, US Gov. Print. Office, Washington, D.C.
  • Walkley, A. and Black, I.A. (1934). An examination of the Degtjareff method for determining soil organic matter and a proposed modification of the chromic acid titration method. Soil Science 37: 29-38.
  • Watt, H. (1863) A dictionary of chemistry, vols. 1-4. London: Longman, Green, Longman, Roberts and Green.
  • Further information and acknowledgements

    See Goulding et al (2000) for measurements of nitrate leaching from the Broadbalk wheat experiment from 1990-1999 (Key References below).

    With thanks to Andy Macdonald, Paul Poulton and Steve Freeman for help with compiling the data and text.

    Key References

    2021

    • Thomas, C. L. , Hernandez-Allica, J. , Dunham, S. J. , Mcgrath, S. P. and Haefele, S. M.(2021) "A comparison of soil texture measurements using mid-infrared spectroscopy (MIRS) and laser diffraction analysis (LDA) in diverse soils", Scientific Reports, 11, 16
      DOI: 10.1038/s41598-020-79618-y
    • Suravi, K. N. , Attenborough, K. , Taherzadeh, S. , Macdonald, A. J. , Powlson, D. S. , Ashton, R. W. and Whalley, W. R.(2021) "The effect of organic carbon content on soil compression characteristics", Soil and Tillage research, 209, 104975
      DOI: 10.1016/j.still.2021.104975

    2020

    • Redmile-Gordon, M. , Gregory, A. S. , White, R. P. and Watts, C. W.(2020) "Soil organic carbon, extracellular polymeric substances (EPS), and soil structural stability as affected by previous and current land use", Geoderma, 363
      DOI: 10.1016/j.geoderma.2019.114143
    • Jensen, J. L. , Schjonning, P. , Watts, C. W. , Christensen, B. T. , Obour, P. B. and Munkholm, L. J.(2020) "Soil degradation and recovery - Changes in organic matter fractions and structural stability", Geoderma, 364
      DOI: 10.1016/j.geoderma.2020.114181

    2012

    • Powlson, D. S. , Bhogal, A. , Chambers, B. J. , Coleman, K. , Macdonald, A. J. , Goulding, K. W. T. and Whitmore, A. P.(2012) "The potential to increase soil carbon stocks through reduced tillage or organic material additions in England and Wales: A case study.", Agriculture, Ecosystems & Environment, 146, 23-33
      DOI: 10.1016/j.agee.2011.10.004

    2010

    • Gregory, A. S. , Bird, N. R. A. , Whalley, W. R. , Matthews, G. P. and Young, I. M.(2010) "Deformation and Shrinkage Effects on the Soil Water Release Characteristic", Soil Science Society of America Journal, 74, 1104-1112
      DOI: 10.2136/sssaj2009.0278

    2009

    • Gregory, A. S. , Watts, C. W. , Griffiths, B. S. , Hallett, P. D. , Kuan, H. L. and Whitmore, A. P.(2009) "The effect of long-term soil management on the physical and biological resilience of a range of arable and grassland soils in England", Geoderma, 153, 172-185
      DOI: 10.1016/j.geoderma.2009.08.002

    2008

    • Jenkinson, D. S. , Poulton, P. R. and Bryant, C.(2008) "The turnover of organic carbon in subsoils. Part 1. Natural and bomb radiocarbon in soil profiles from the Rothamsted long-term field experiments", European Journal of Soil Science, 59, 391-399
      DOI: 10.1111/j.1365-2389.2008.01025.x

    2006

    • Watts, C. W. , Clark, L. J. , Poulton, P. R. , Powlson, D. S. and Whitmore, A. P.(2006) "The role of clay, organic carbon and long-term management on mouldboard plough draught measured on the Broadbalk wheat experiment at Rothamsted", Soil Use and Management, 22, 334-341
      DOI: 10.1111/j.1475-2743.2006.00054.x

    2003

    • Blake, L. , Johnston, A. E. , Poulton, P. R. and Goulding, K. W. T.(2003) "Changes in soil phosphorus fractions following positive and negative phosphorus balances for long periods.", Plant and Soil, 254, 245-261
      DOI: 10.1023/A:1025544817872

    2000

    • Goulding, K. W. T. , Poulton, P. R. , Webster, C. P. and Howe, M. T.(2000) "Nitrate leaching from the Broadbalk Wheat Experiment, Rothamsted, UK, as influenced by fertilizer and manure inputs and the weather", Soil Use and Management, 16, 244-250
      DOI: 10.1111/j.1475-2743.2000.tb00203.x
    • Blake, L. , Mercik, S. , Koerschens, M. , Moskal, S. , Poulton, P. R. , Goulding, K. W. T. , Weigel, A. , Powlson, D. S. , Falloon, P. D. and Smith, P.(2000) "Phosphorus content in soil, uptake by plants and balance in three European long-term field experiments. Modelling refractory soil organic matter", Nutrient Cycling in Agroecosystems, 56, 263-275
      DOI: 10.1023/A:1009841603931

    1999

    • Blake, L. , Mercik, S. , Koerschens, M. , Goulding, K. W. T. , Stempen, S. , Weigel, A. , Poulton, P. R. and Powlson, D. S.(1999) "Potassium content in soil, uptake in plants and the potassium balance in three European long-term field experiments", Plant and Soil, 216, 1-14
      DOI: 10.1023/a:1004730023746

    1995

    1980

    • Avery, B. W.(1980) "Soil classification for England and Wales (higher categories). ", Technical Monograph 14, Soil Survey of England and Wales, Harpenden UK , ,

    1972

    • Bolton, J.(1972) "Changes in magnesium and calcium in soils of the Broadbalk wheat experiment at Rothamsted from 1865 to 1966", Journal of Agricultural Science, 79, 217-223
      DOI: 10.1017/S0021859600032184

    1969

    • Salter, P. J. and Williams, J. B.(1969) "The moisture characteristics of some Rothamsted, Woburn and Saxmundham soils", Journal of Agricultural Science, 73, 155-156
      DOI: 10.1017/S0021859600024242
    • Johnston, A. E.(1969) "The soils of Broadbalk: Plant nutrients in Broadbalk soils", Rothamsted Experimental Station Report for 1968 , Part 2 , 93-115
      Get from eRAdoc: ResReport1968p2-93-115
    • Avery, B. W. and Bullock, P.(1969) "The soils of Broadbalk: Morphology and classification of Broadbalk soils", Rothamsted Experimental Station Report for 1968 , , 63-81 with references pp 112-115
      Get from eRAdoc: ResReport1968p2-63-81

    1902

    Site details, plot area, soil moisture and drainage, soil description and texture and soil weights

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    Broadbalk site and soil physical properties

    The Broadbalk wheat experiment, established in the autumn of 1843, has been cultivated since at least 1623, and probably much earlier (Avery & Bullock, 1969). In his first Rothamsted paper, published in 1847, Lawes described the soil as "a heavy loam resting upon chalk, capable of producing good wheat when well manured" . Here, details are given of the site, the soil description and standard soil weights.

    Site details

    • Location: Rothamsted Research, Harpenden, Herts, AL5 2JQ, UK
    • Latitude: 51 degrees 48 mins 36 secs North
    • Longitude: 0 degrees 22 mins 30 secs West
    • GB Grid Reference: TL123 136
    • Gradient: A slope of 1 degree, West to East
    • Irrigation: There is no irrigation

    Plot area

    When the experiment was established in 1843 most of the plots were very large. Most comprised an ‘a’ and ‘b’ half (each 3.77m wide) and were 320m long (the length of the field). Plots 21 and 22 are a little narrower. In 1894 the two halves were combined, giving a total plot area of 0.24ha. As the experiment progressed these large plots have been subdivided into different Sections (see Plans and treatments for more details), with corresponding changes in the area harvested. The current plot lengths vary depending on the Section and are between 15.24m (Section 0) and 28.04m (Section 1). The plots are now 6m wide (except plots 21 and 22 which are 4m wide) with 48 rows at 12.5 cm spacing. The harvested area is 2.1m wide. The harvested area is shown in most of the datasets.

    Soil moisture and drainage

    Soil Moisture Characteristics: With nearly 200 plots in the experiment, there isn't water retention information for all treatments. Water retention characteristics for contrasting plots can be found in Salter & Williams (1969). For more recent information, see Gregory et al, 2010, where retention characteristics have been fitted to the van Genuchten model.

    Soil Drainage: Lawes described the soil of Broadbalk as having good natural drainage. However, as it was an experimental field, it was decided to improve the drainage, to allow greater access. Tile drains were installed under each strip in autumn 1849 (except plot 20). They were installed in the centre of the strip, under the furrow separating the 'a' and 'b' halves (see Plan 1852-1925). Tiles drains were installed under strip 2.1 (2A) in autumn 1884 before the first application of FYM. Tile drains were 5cm in diameter and 60-76 cm deep, and they discharged into a 10cm diameter main drain at the east side of the field.

    Lawes and Gilbert realised that the drains could be used to measure losses of plant nutrients from the different fertilizer treatments. Small outlet pits were dug at the intersection of each strip drain and the main drain in December 1866 to sample the water draining from strips 2 to 16. This was not ideal, as there was the risk of the samples being contaminated. The drains from strips 17-19 were opened in November 1878. In spring 1879 the collection of drainage water was improved, with the drains from each strip discharging into their own pit, which overflowed into a separate, deepened main drain which was kept open. In 1897/98 this main drainage ditch was enlarged, the base concreted and the sides bricked. (Details from Johnston & Garner, 1969).

    1623 map
    Map of 1623 showing field which became the Broadbalk experiment under arable cultivation

    Broadbalk harvest
    Broadbalk spreading chalk in 1954, Section V

    Broadbalk sampling
    Broadbalk 1935, tractor plough

    Soil description

    • FAO Classification: Chromic Luvisol (or Alisol)
    • U.S. Soil Taxonomy: Aquic (or Typic) Paleudalf
    • Soil Survey of England & Wales Group: Stagnogleyic paleo-argillic brown earth (Avery, 1980)
    • Soil Survey of England & Wales Series: Predominately Batcombe Series (Avery & Catt, 1995 - see Soil Map link on left hand side).

    For more details of the Batcombe and other soil series, see Cranfield University 2018 Soils Guide.

    Soil texture class: Clay loam to silty clay loam over clay-with flints. The soils contain a large number of flints and are slightly calcareous. Below about 2m depth the soil becomes chalk. The experiment is under-drained and the site is free draining.

    Soil texture, 0-23cm (from Gregory et al, 2010)

    • Sand (2000 - 63 µm) : 25 %
    • Silt (63 - 2 µm) : 50 %
    • Clay (<2 µm) : 25 %
    • Particle density g cm -3 : 2.56 %

    There is considerable variation in soil texture across the site, with clay contents ranging from 19 - 39% (Watts et al, 2006). The mean clay content for Sections 0 (straw incorporated since 1986) and 1 (straw removed, both continuous wheat) is 28.3% (Watts et al, 2006). Clay content increases with soil depth in the Batcombe Series (from Jenkinson et al, 2008):

    • 23-46 cm : 30 % clay
    • 46-69 cm : 50 % clay
    • 69-92 cm : 49 % clay

    Soil pH: The plough layer (0-23 m) is limed when necessary to maintain a minimum soil pH of 7.0 - 7.5. Broadbalk was first limed regularly from 1955-1967, with plots given the larger inputs of ammonium fertilizers receiving more lime than the controls. Liming stopped from 1968-1975, but began again in 1976-1992, with 3 or 4 sections being limed each year, with 2.9t/ha of chalk being applied each autumn to all plots of each section. From 2007 onward selected plots have been limed every 5-6 years based on soil pH measurements to maintain top-soil pH around 7.0-7.5. Selected plots were limed in autumn 2018.

    Soil weights, Mkg/ha

    The following standard soil weights should be used for Broadbalk soil, both continuous wheat and rotational sections. All weights are in 106 kg/ha of oven-dry fine soil. To convert to g/cm3 divide by depth in cm (eg 23) and multiply by 10. Data prepared by A J Macdonald and P R Poulton, February 2014.

    Broadbalk standard soil weights 106 kg/ha, 0-23cm

    Year Inorganic a
    Plots 03-20
    FYM since 1844 b
    Plot 2.2 (2B)
    FYM since 1885 b
    Plot 2.1 (2A)
    FYM 1968-2000 c
    Plot 01
    1843
    1865
    1881
    1884
    1893
    1914
    1967
    2000
    2010
    (2.88)
    2.88
    2.88
    2.88
    2.88
    2.88
    *
    2.88
    2.88
    (2.88)
    2.78
    2.69
    *
    2.62
    2.60
    *
    2.52
    2.52
    *
    *
    *
    (2.88)
    2.81
    2.75
    *
    2.52
    2.52
    *
    *
    *
    *
    *
    *
    (2.88)
    2.52
    (2.63)

    Broadbalk standard soil weights 106 kg/ha, 23-46cm

    Year Plots 03-20 Plot 2.2 (2B) Plot 2.1 (2A) Plot 01
    All years
    3.0
    3.0
    3.0
    3.0

    Broadbalk standard soil weights 106 kg/ha, 46-69cm and 69-91cm

    Year Plots 03-20 Plot 2.2 (2B) Plot 2.1 (2A) Plot 01
    All years
    3.1
    3.1
    3.1
    3.1

    Topsoil data is the mean of comprehensive measurements of soil weight made in 1865, 1881, 1893, 1914 and 2000. Figures in brackets are assumed. * indicates no samples taken. 23-46cm is the mean of all plots measured in 1865, 1881, 1893 and 1914. 46-69cm and 69-91cm is the mean of all plots measured in 1865, 1881 and 1893. See Dyer, 1902 for 1865, 1881 and 1893 data. See Watts et al, 2006 for 2000 data. 1914 data is previously unpublished.

    Notes:

    a Plots 03-20, receiving inorganic fertilizer only, no manure (FYM). This also includes plot 03, given no fertilizer, and plot 19, recieving rape cake/castor meal.

    b Assume no further change in bulk density/soil weight on plots 2.1 and 2.2 after 2000. However, BD may increase slightly on plots in rotation as FYM is NOT applied to the oats.

    c BD will increase on plot 01 as applications of FYM stopped in 2000.The increase is assumed to be at the same rate as the decrease in BD between 1968-2000.

    For deeper soil layers, use the following weights, taken from Dyer, 1902:

    Depth
    cm
    Plots Soil weight, 106 kg/ha Soil weight, g/cm3
    91-114
    114-137
    137-160
    160-183
    183-206
    206-229
    All plots
    All plots
    All plots
    All plots
    All plots
    All plots
    3.21
    3.18
    3.20
    3.22
    3.37
    3.37
    1.40
    1.38
    1.39
    1.40
    1.47
    1.47

    Acknowledgements

    With thanks to Andy Macdonald and Paul Poulton for help with compiling the information and text.

    Key References

    2021

    • Thomas, C. L. , Hernandez-Allica, J. , Dunham, S. J. , Mcgrath, S. P. and Haefele, S. M.(2021) "A comparison of soil texture measurements using mid-infrared spectroscopy (MIRS) and laser diffraction analysis (LDA) in diverse soils", Scientific Reports, 11, 16
      DOI: 10.1038/s41598-020-79618-y
    • Suravi, K. N. , Attenborough, K. , Taherzadeh, S. , Macdonald, A. J. , Powlson, D. S. , Ashton, R. W. and Whalley, W. R.(2021) "The effect of organic carbon content on soil compression characteristics", Soil and Tillage research, 209, 104975
      DOI: 10.1016/j.still.2021.104975

    2020

    • Redmile-Gordon, M. , Gregory, A. S. , White, R. P. and Watts, C. W.(2020) "Soil organic carbon, extracellular polymeric substances (EPS), and soil structural stability as affected by previous and current land use", Geoderma, 363
      DOI: 10.1016/j.geoderma.2019.114143
    • Jensen, J. L. , Schjonning, P. , Watts, C. W. , Christensen, B. T. , Obour, P. B. and Munkholm, L. J.(2020) "Soil degradation and recovery - Changes in organic matter fractions and structural stability", Geoderma, 364
      DOI: 10.1016/j.geoderma.2020.114181

    2012

    • Powlson, D. S. , Bhogal, A. , Chambers, B. J. , Coleman, K. , Macdonald, A. J. , Goulding, K. W. T. and Whitmore, A. P.(2012) "The potential to increase soil carbon stocks through reduced tillage or organic material additions in England and Wales: A case study.", Agriculture, Ecosystems & Environment, 146, 23-33
      DOI: 10.1016/j.agee.2011.10.004

    2010

    • Gregory, A. S. , Bird, N. R. A. , Whalley, W. R. , Matthews, G. P. and Young, I. M.(2010) "Deformation and Shrinkage Effects on the Soil Water Release Characteristic", Soil Science Society of America Journal, 74, 1104-1112
      DOI: 10.2136/sssaj2009.0278

    2009

    • Gregory, A. S. , Watts, C. W. , Griffiths, B. S. , Hallett, P. D. , Kuan, H. L. and Whitmore, A. P.(2009) "The effect of long-term soil management on the physical and biological resilience of a range of arable and grassland soils in England", Geoderma, 153, 172-185
      DOI: 10.1016/j.geoderma.2009.08.002

    2008

    • Jenkinson, D. S. , Poulton, P. R. and Bryant, C.(2008) "The turnover of organic carbon in subsoils. Part 1. Natural and bomb radiocarbon in soil profiles from the Rothamsted long-term field experiments", European Journal of Soil Science, 59, 391-399
      DOI: 10.1111/j.1365-2389.2008.01025.x

    2006

    • Watts, C. W. , Clark, L. J. , Poulton, P. R. , Powlson, D. S. and Whitmore, A. P.(2006) "The role of clay, organic carbon and long-term management on mouldboard plough draught measured on the Broadbalk wheat experiment at Rothamsted", Soil Use and Management, 22, 334-341
      DOI: 10.1111/j.1475-2743.2006.00054.x

    2003

    • Blake, L. , Johnston, A. E. , Poulton, P. R. and Goulding, K. W. T.(2003) "Changes in soil phosphorus fractions following positive and negative phosphorus balances for long periods.", Plant and Soil, 254, 245-261
      DOI: 10.1023/A:1025544817872

    2000

    • Goulding, K. W. T. , Poulton, P. R. , Webster, C. P. and Howe, M. T.(2000) "Nitrate leaching from the Broadbalk Wheat Experiment, Rothamsted, UK, as influenced by fertilizer and manure inputs and the weather", Soil Use and Management, 16, 244-250
      DOI: 10.1111/j.1475-2743.2000.tb00203.x
    • Blake, L. , Mercik, S. , Koerschens, M. , Moskal, S. , Poulton, P. R. , Goulding, K. W. T. , Weigel, A. , Powlson, D. S. , Falloon, P. D. and Smith, P.(2000) "Phosphorus content in soil, uptake by plants and balance in three European long-term field experiments. Modelling refractory soil organic matter", Nutrient Cycling in Agroecosystems, 56, 263-275
      DOI: 10.1023/A:1009841603931

    1999

    • Blake, L. , Mercik, S. , Koerschens, M. , Goulding, K. W. T. , Stempen, S. , Weigel, A. , Poulton, P. R. and Powlson, D. S.(1999) "Potassium content in soil, uptake in plants and the potassium balance in three European long-term field experiments", Plant and Soil, 216, 1-14
      DOI: 10.1023/a:1004730023746

    1995

    1980

    • Avery, B. W.(1980) "Soil classification for England and Wales (higher categories). ", Technical Monograph 14, Soil Survey of England and Wales, Harpenden UK , ,

    1972

    • Bolton, J.(1972) "Changes in magnesium and calcium in soils of the Broadbalk wheat experiment at Rothamsted from 1865 to 1966", Journal of Agricultural Science, 79, 217-223
      DOI: 10.1017/S0021859600032184

    1969

    • Salter, P. J. and Williams, J. B.(1969) "The moisture characteristics of some Rothamsted, Woburn and Saxmundham soils", Journal of Agricultural Science, 73, 155-156
      DOI: 10.1017/S0021859600024242
    • Johnston, A. E.(1969) "The soils of Broadbalk: Plant nutrients in Broadbalk soils", Rothamsted Experimental Station Report for 1968 , Part 2 , 93-115
      Get from eRAdoc: ResReport1968p2-93-115
    • Avery, B. W. and Bullock, P.(1969) "The soils of Broadbalk: Morphology and classification of Broadbalk soils", Rothamsted Experimental Station Report for 1968 , , 63-81 with references pp 112-115
      Get from eRAdoc: ResReport1968p2-63-81

    1902

    Information about the weed surveys on Section 8 (no herbicides), 1991-present, and earlier surveys on the whole experiment, 1933-1979.

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    Broadbalk Weeds

    The Broadbalk experiment was started in 1843 to investigate the relative importance of different plant nutrients (N, P, K, Na, Mg) on grain yield of winter wheat. Weeds were controlled initially by hand hoeing and fallowing, but since 1964, herbicides have been applied to the whole experiment with the exception of Section 8. This is one of the few arable sites in the country where herbicides have never been applied. Weed surveys have been carried out annually in two phases, the first between 1933-1979 and the second from 1991-present day. There are earlier records too, with the first plot-by-plot surveys of weed species done in 1869 recording the presence of 23 species in stubble in September. Since then, approximately 130 weed species have been recorded on Broadbalk Section 8, but many of these only occur sporadically and about 30 of these are currently recorded annually (Species list 1869-2018). This site also provides an invaluable reserve for seven nationally rare or uncommon species including corn cleavers (Galium tricornutum), corn buttercup (Ranunculus arvensis), shepherd’s needle (Scandix pecten-veneris) and prickly poppy (Papaver argemone). This is now the only location in the UK where corn cleavers is known to occur naturally (see below). This resource and associated data enables various weed investigations including weed population ecology, studies on the effects of fallowing on the weed seed bank, seed dormancy and persistence, agroecology, and population dynamics of individual weed species. Recently, molecular approaches have been used to study the genetic diversity of weeds found on Section 8, this rare herbicide-free arable plot.

    Section 8 was fallowed in 2015 and 2016 so there is no data for these years.

    Current Survey 1991 to present

    The current weed survey was started on Section 8 in 1991 and has continued annually ever since - although not on years when that section is in fallow i.e. 1994, 2001, 2008, 2015 & 2016. It was fallowed in 2015 and 2016 in order to reduce an infestation of Rumex obtusifolius in particular (see table below). Section 8 (called section VA 1958-1967) was created in 1968 when the experiment was divided into its present layout (Broadbalk plan today). The current assessment method records the presence of individual weed species in 25 random quadrats (0.1m2) per plot. Each year all 18 plots are surveyed meaning 450 quadrats are assessed per year, usually in June. Frequencies refer to the total number of quadrats in which a weed is recorded, the maximum being 25 per plot and 450 across all plots in the section. This method is more appropriate for detecting long-term trends in weed frequencies and population differences between plots than the earlier surveys (below) and provides a comprehensive set of 20 years of data for weed studies.

    Galium tricornutum Section 8 Broadbalk
    Corn cleavers

    (Galium tricornutum) in Broadbalk

    Non-herbicide plot section 8 Broadbalkp
    Weeds species in Broadbalk

    non-herbicide Section 8 in early summer

    Broadbalk elevated view
    Elevated view of Broadbalk

    Section 8 weeds, mid-view, in late summer

    Galium tricornutum Section 8 Broadbalk
    Corn buttercup

    Ranunculus arvensis

    Non-herbicide plot section 8 Broadbalkp
    Shepherd's needle

    Scandix pecten-veneris

    Broadbalk elevated view
    Field poppy

    Papever rhoeas

    Data is presented in e-RA as the following datasets:

    BKWEEDS_SUM: A summary of annual total frequencies for section 8 1991-present.

    BKWEEDS_PLOT: Annual frequencies of each species per plot for section 8 1991-present.

    There have been 53 species recorded in total since 1991 [species list 1991-2018] but on average there are 31 species found per year (with a maximum of 38 in 1993 & 1995 and a minimum of 26 in 2009) and there has been a gradual slight decline over the period. The long dataset allows general, overall trends to be observed and weed species are seen to differ greatly in their response to a given set of conditions, some declining, some increasing and others fluctuating - for example a decline in Papaver rhoeas between 1999 and 2003, and subsequent recovery (for which there is no obvious explanation). Of the species currently recorded annually ten species are locally common on many plots: Blackgrass (Alopecurus myosuroides), field poppy (Papaver rhoeas), common vetch (Vicia sativa), parsley-piert (Aphanes arvensis), scentless mayweed (Tripleurospermum inodorum), shepherd's needle (Scandix pectin-veneris), chickweed (Stellaria media), venus's looking glass (Legousia hybrida), creeping thistle (Cirsium arvense) and black medic (Medicago lupulina). A principal components analysis of the 1991-2002 survey data for 15 species showed clearly the influence of inorganic N fertiliser levels on the frequency of individual species. The frequency of one species (common chickweed (Stellaria media)) was greatly favoured by increasing amounts of nitrogen fertiliser from 0 to 288 kg N ha-1, others were strongly disadvantaged (e.g., black medic (Medicago lupulina) and horsetail (Equisetum arvense)), some were slightly disadvantaged (e.g., common vetch (Vicia sativa) and parsley-piert (Aphanes arvensis)), and some showed little response to differing N rates (e.g., blackgrass (A. myosuroides) and poppy (P. rhoeas)) (Moss et. al 2004).

    Corn cleavers (Galium tricornutum) is one of the rarest plants in the UK and this occurence on Broadbalk is the last known site in the UK. Numbers have increased from under five individuals in the 1990's to over 450 in 2011 and this has been a consequence of our active management strategy.

    The commonest species on Broadbalk:

    20-year* mean frequency (max = 450 quadrats) for 19 species occurring in a mean minimum of 20 quadrats

    Rank
    Species listed in order of frequency
    (20 yr mean)
    20 year mean
    1991 - 2013
    2014
    frequency
    2014
    as % of 20 yr mean
    1
    Alopecurus myosuroides
    448
    450
    100
    2
    Papaver rhoeas
    341
    351
    103
    3
    Vicia sativa
    270
    347
    129
    4
    Aphanes arvensis
    260
    163
    63
    5
    Tripleurospermum inodorum
    257
    249
    97
    6
    Scandix pecten-veneris
    180
    191
    106
    7
    Stellaria media
    155
    300
    194
    8
    Legousia hybrida
    125
    72
    57
    9
    Cirsium arvense
    117
    124
    106
    10
    Medicago lupulina
    101
    61
    60
    11
    Veronica persica
    83
    79
    95
    12
    Polygonum aviculare
    83
    20
    24
    13
    Equisetum arvense
    81
    59
    72
    14
    Odontites verna
    73
    36
    49
    15
    Ranunculus arvensis
    69
    64
    93
    16
    Viola arvensis
    53
    1
    2
    17
    Veronica arvensis
    39
    18
    46
    18
    Minuartia hybrida
    22
    23
    105
    19
    Rumex obtusifolius
    20
    97
    469

    * 20 years of records taken over 23 years (not in those years when section 8 was fallow i.e. 1994, 2001 and 2008)

    Galium tricornutum Section 8 Broadbalk
    Meadow vetchling

    Lathyrus pratensis

    Non-herbicide plot section 8 Broadbalkp
    Horsetail

    Equisetum arvense

    Broadbalk elevated view
    Chickweed

    Stellaria media

    Galium tricornutum Section 8 Broadbalk
    Dwarf spurge

    Euphorbia exigua

    Non-herbicide plot section 8 Broadbalkp
    Black medick

    Medicago lupilina

    Broadbalk elevated view
    Common vetch

    Vicia sativa

    Earlier surveys 1933-1967 and 1968-1979

    Annual surveys were conducted from 1933 to 1979. Originally, there were no sections on Broadbalk, just long strips the length of the whole field (Broadbalk plan 1852-1926). In 1926 the field was divided into 5 sections (I-V) (Broadbalk plan 1926). The whole field length was sampled for weeds as no herbicide weed control took place, just fallowing every five years. This gave all plot and section combinations (between 90 and 129 plots per year). After 1968, it was divided in to ten sections (Broadbalk plan 1996-2017) and again the whole field was surveyed each year - enabling comparison of weeds with and without herbicides.

    This appears to be an excellent resource, however, it has not been widely used, principally because of the inconsistent frequency categories used. Neither were quadrats used, rather the assessor walked in a zig-zag pattern along the plot noting all weeds within 45cm of the plot boundary. Consequently there is a limitation on the interpretation of the data for ecological studies. The codes used to indicate species presence and abundance (termed STATE in the database) include the following:

    0 Occasional
    0+ Between 0 and T
    T Distributed
    T+ Between T and P
    P Plentiful
    P+ Between P and PP
    PP Very plentiful
    PP+ Between PP and PPP
    PPP Extremely plentiful

    The following datasets are available:

    BBKWEEDS_FAL for 1933-67 (FAL indicating fallow) - herbicides applied from 1964 to all sections except VA (which became section 8 in 1968). Data for all sections and all plots.

    BBKWEEDS_ROT for 1968-79 (ROT indicating rotation with other crops, though not on section 8 which is rotated only with fallow): - herbicides applied throughout to all sections except 8. Data for all sections and all plots.

    During these years, surveys were conducted twice yearly, usually in May and August (sometimes as early as April or as late as September). Supplementary surveys were done for special purposes such as for blackgrass which is not obvious in the early season surveys and become more obvious in the summer when flowering. It is recommended that you extract both STATE and SPEC_REMARK since the presence of a species may be indicated by a remark such as 'patch' even though there is no code for the state. In view of the large number of null values it is probably best to tick the checkbox for STATE and exclude 'null' and '-', meaning none. In these datasets, dates are termed START DAY rather than year, as there are two surveys each year.

    There were 114 species names recorded during 1933-1967 [species list 1933-1967] and 113 species names during the 1968-79 surveys [species list 1968-79].

    Earlier surveys - data not included in e-RA:

    Originally, there were no sections on Broadbalk, just long strips the length of the whole field (Broadbalk plan 1852-1926). The first plot-by-plot list of weed species was done in 1869 and recorded the presence of 25 species in stubble in September [species list 1869] (Thurston, 1969). Hand weeding and hoeing was practiced but due to the shortage of labour during the 1914-18 war the field became very weedy. Between 1926-1929 the field was fallowed to eliminate weeds, three out of five sections fallowed for 2 years running (Broadbalk plan 1926-1966). From 1931 a regular cycle of fallowing 1 year in five was introduced and the effect of fallow on weed seeds was studied (Brenchley & Warington 1930). Routine plot-by-plot surveys were started in 1930 and made twice yearly; first in May after spring germinating weeds are large enough to identify without trampling the crop and secondly, after the crop is cut and harvested which showed late germinating species.

    Further information and references

    The review paper by Moss et al. (2004) provides the most recent summary of weed studies on Broadbalk. The Thurston (1969) report provides additional information on the earlier surveys. References in both papers provide comprehensive coverage of other studies. For more details, refer to the Rothamsted Guide to the Classical Experiments 2018 pages 15-16 or contact the e-RA Curators.

    Acknowledgements: With thanks to Stephen Moss, Jon Storkey, Richard Hull and Graham Shephard (VCU) for help with compiling images and data.

    Note on herbicides: Applied to section 1A from 1957; to VB from 1963; and to all other sections (except VA which became section 8 in 1968) from 1964.

    Notes on species: These include records of volunteer plants such as potatoes and both names for species names which have changed.

    List of Latin and common names of species in current Broadbalk Survey.

    Galium tricornutum Section 8 Broadbalk
    Groundsel

    Senecio vulgaris

    Non-herbicide plot section 8 Broadbalk
    Plot 3 Section 8 Broadbalk

    Broadbalk elevated view
    Plot 21 Section 8 Broadbalk

    Key References

    2021

    • Storkey, J. , Mead, A. , Addy, J. and Macdonald, A.(2021) "Agricultural intensification and climate change have increased the threat from weeds", Global Change Biology, 00, 1-10
      DOI: 10.1111/gcb.15585
    • Le Coeur, C. , Storkey, J. and Ramula, S.(2021) "Population responses to observed climate variability across multiple organismal groups", Oikos, 130, 476-487
      DOI: 10.1111/oik.07371

    2018

    • Storkey, J. and Neve, P.(2018) "What good is weed diversity?", Weed Research, 58, 239-243
      DOI: 10.1111/wre.12310
    • Metcalf, H. , Milne, A. E. , Hull, R. , Murdoch, A. J. and Storkey, J.(2018) "The implications of spatially variable pre-emergence herbicide efficacy for weed management", Pest Management, 74, 755-765
      DOI: 10.1002/ps.4784

    2014

    • Garcia De Leon, D. , Storkey, J. , Moss, S. R. and Gonzalez-Andujar, J. L.(2014) "Can the storage effect hypothesis explain weed co-existence on the Broadbalk long-term fertiliser experiment?", Weed Research, 54, 445-456
      DOI: 10.1111/wre.12097

    2010

    • Storkey, J. , Moss, S. R. and Cussans, J. W.(2010) "Using Assembly Theory to Explain Changes in a Weed Flora in Response to Agricultural Intensification", Weed Science, 58, 39-46
      DOI: 10.1614/ws-09-096.1

    2004

    • Moss, S. R. , Storkey, J. , Cussans, J. W. , Perryman, S. a. M. and Hewitt, M. V.(2004) "The Broadbalk long-term experiment at Rothamsted: what has it told us about weeds?", Weed Science, 52, 864-873
      DOI: 10.1614/WS-04-012R1

    2000

    1969

    1964

    • Thurston, J. M.(1964) "Weed studies in winter wheat", Proceedings of the 7th British Weed Control Conference Vol. II, 592-598

    1958

    • Warington, K.(1958) "Changes in the Weed Flora on Broadbalk Permanent Wheat Field During the Period 1930-55", Journal of Ecology, 46, 101-113

    1945

    • Brenchley, W. E. and Warington, K.(1945) "The influence of periodic fallowing on the prevalence of viable weed seeds in arable soil", Annals of Applied Biology, 32, 285-296

    1936

    • Warington, K.(1936) "The effect of constant and fluctuating temperature on the germination of the weed seeds in arable soil", Journal of Ecology, 24, 185-204
    • Brenchley, W. E. and Warington, K.(1936) "The weed seed population of arable soil. III. The re-establishment of weed species after reduction by fallowing", Journal of Ecology, 24, 479-501

    1933

    • Brenchley, W. E. and Warington, K.(1933) "The weed seed population of arable soil. II. Influence of crop, soil and methods of cultivation upon the relative abundance of viable seeds.", Journal of Ecology, 21, 103-127

    1930

    • Brenchley, W. E. and Warington, K.(1930) "The weed seed population of arable soil. I. Numerical estimation of viable seeds and observations on their natural dormancy", Journal of Ecology, 18, 235-272

    1924

    • Warington, K.(1924) "The influence of manuring on the weed flora of arable land", Journal of Ecology, 12, 111-126

    Description of harvest methods and datasets available

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    Broadbalk Yields

    Wheat grain and straw yields have been recorded every year since the experiment began, with the first harvest in 1844 (the crop was sown in autumn 1843). Dried grain and straw samples have also been kept for chemical analysis since 1844; these are preserved in the Rothamsted Sample Archive.
    Yield data is held in four datasets, which reflect the changes to the experimental layout and harvesting techniques:

    BKYIELD Broadbalk wheat grain and straw yields 1844-1925
    BKYIELD_F Broadbalk wheat grain and straw yields 1926-1953
    BKYIELD_F85 Broadbalk wheat grain and straw yields 1954-1967
    BKYIELD_R85 Broadbalk wheat grain and straw yields 1968-current year

    See Plans and treatments for more details of changes to the experimental layout over time.

    See List of key dates, including sowing and harvest dates.

    Harvesting:
    From 1844 to 1901 the wheat crop was cut by hand by scythes, from 1902 to 1956 a self-binder was used, originally horse drawn, and then powered by a tractor. Hand cutting with scythes was often necessary if the ground was very wet or the crop was badly lodged (flattened). After cutting the crop was bound into sheaves which were ‘stooked’ and left on the plot for about two weeks then ‘carted into barns where they were threshed over the winter. Cutting and carting may have been spread over several days. Thus the earlier datasets BBKYIELD and BBKYIELD_F include the dates of both cutting and carting the crop. From 1957 the plots have been harvested by a small plot combine harvester; only the central strip of each plot is taken for yield and samples. Before 1957 the plots were usually cut in early August, since 1957 combining has been in August or early September. Sowing and harvest dates are available from the e-RA Curators.

    Yields from Section 8 (no herbicides):
    Section 8 has never received herbicides, and many weed species are present. Many weed seeds and other weed debris are included in the 'grain' yield at harvest. The 'straw' will also include weed material. The FYM plots and plots given the higher N rates generally have more weed contamination than the other plots. A sub-sample of grain is cleaned (weed seeds and debris removed) after harvest, and an estimate of the cleaned grain yield made. Data currently in e-RA is of the uncleaned grain. It is not possible to correct the straw yield for weed contamination. For further details, and the cleaned grain data, please contact the e-RA Curators

    Units:
    Since 1954 dry matter (DM) content of the grain and straw has been measured at harvest, and all yields have been converted to 85% DM (datasets BKYIELD_F85 and BKYIELD_R85). Before 1954 DM content was not measured and the yields are expressed at the DM content at which they were harvested (around 85% DM).

    Corrections:
    2013 plot 17 Section 3, no straw yield was recorded. An estimated value has been used, based on the straw/grain ratio of plot 16, Section 3 (a plot with similar grain yield): (5.44/8.01) * 7.95 = 5.39 t/ha.

    Broadbalk sampling
    Broadbalk harvest 1880, hand cutting with scythes

    Broadbalk harvest
    Broadbalk harvest 1935, horse-drawn reaper-binder

    Broadbalk sampling
    Broadbalk harvest 1935, tractor binder

    Key References

    2021

    • Rothamsted_Research(2021) "Broadbalk Wheat Experiment cropping 1843-2021", Electronic Rothamsted Archive, Rothamsted Research, Harpenden, Herts, AL5 2JQ, UK
      DOI: 10.23637/rbk1-crop1843-2021-01
    • Rothamsted_Research(2021) "Broadbalk Wheat Experiment plan and cropping since 2018", Electronic Rothamsted Archive, Rothamsted Research, Harpenden, Herts, AL5 2JQ, UK
      DOI: 10.23637/rbk1-today2018-02
    • Rothamsted_Research(2021) "Broadbalk Wheat Experiment plan and cropping 1968-2017", Electronic Rothamsted Archive, Rothamsted Research, Harpenden, Herts, AL5 2JQ, UK
      DOI: 10.23637/rbk1-plan1968-2017-01
    • Rothamsted_Research(2021) "Broadbalk Wheat Experiment plan and cropping 1926-1967", Electronic Rothamsted Archive, Rothamsted Research, Harpenden, Herts, AL5 2JQ, UK
      DOI: 10.23637/rbk1-plan1926-67-02
    • Glendining, M. J. and Poulton, P. R.(2021) "Broadbalk Wheat Experiment plan and cropping 1852-1925", Electronic Rothamsted Archive, Rothamsted Research, Harpenden, Herts, AL5 2JQ, UK
      DOI: 10.23637/rbk1-sup-1534342858-02
    • Addy, J. W. G. , Ellis, R. H. , Macdonald, A. J. , Semenov, M. A. and Mead, A.(2021) "The impact of weather and increased atmospheric CO2 from 1892 to 2016 on simulated yields of UK wheat", J. R. Soc. Interface, 18, 20210250
      DOI: 10.1098/rsif.2021.0250

    2020

    • Macholdt, J. , Piepho , H.-P. , Honermeier, B. , Perryman, S. , Macdonald, A. and Poulton, P.(2020) "The effects of cropping sequence, fertilization and straw management on the yield stability of winter wheat (19862017) in the Broadbalk Wheat Experiment, Rothamsted, UK", The Journal of Agricultural Science, 158, 6579
      DOI: 10.1017/S0021859620000301
    • Addy, J. W. G. , Ellis, R. H. , Macdonald, A. J. , Semenov, M. A. and Mead, A.(2020) "Investigating the effects of inter-annual weather variation (1968-2016) on the functional response of cereal grain yield to applied nitrogen, using data from the Rothamsted Long-Term Experiments", Agricultural and Forest Meteorology, 284, 107898
      DOI: 10.1016/j.agrformet.2019.107898

    2018

    • Rothamsted_Research(2018) "Broadbalk experiment plan revised 2018", Electronic Rothamsted Archive, Rothamsted Research, Harpenden, Herts, UK.
      DOI: 10.23637/rbk1-today2018-01
    • Rothamsted_Research(2018) "Broadbalk experiment fertilizer and manure treatments, 1852-2021", Electronic Rothamsted Archive, Rothamsted Research, Harpenden, Herts, AL5 2JQ, UK
      DOI: 10.23637/rbk1-FertTreats
    • Johnston, A. E. and Poulton, P. R.(2018) "The importance of long-term experiments in agriculture: their management to ensure continued crop production and soil fertility; the Rothamsted experience. ", European Journal of Soil Science, 69, 113-125
      DOI: 10.1111/ejss.12521

    2016

    • J. Storkey , A.J. Macdonald , J.R. Bell , I.M. Clark , A.S. Gregory , N.J. Hawkins , P.R. Hirsch , L.C. Todman and Whitmore, A. P.(2016) "The Unique Contribution of Rothamsted to Ecological Research at Large Temporal Scales.", Advances in Ecological Research (eds: A.J. Dumbrell , R.L. Kordas and G. Woodward - Academic Press), Vol 55, Chapter 1, pp. 3-42
      DOI: 10.1016/bs.aecr.2016.08.002

    2012

    • Powlson, D. S. , Bhogal, A. , Chambers, B. J. , Coleman, K. , Macdonald, A. J. , Goulding, K. W. T. and Whitmore, A. P.(2012) "The potential to increase soil carbon stocks through reduced tillage or organic material additions in England and Wales: A case study.", Agriculture, Ecosystems & Environment, 146, 23-33
      DOI: 10.1016/j.agee.2011.10.004

    2009

    • Rothamsted_Research(2009) "Broadbalk experiment plan 1996-2017", Electronic Rothamsted Archive, Rothamsted Research, Harpenden, Herts, AL5 2JQ UK
      DOI: 10.23637/rbk1-plan1996-2017-01
    • Johnston, A. E. , Poulton, P. R. and Coleman, K.(2009) "Soil organic matter: its importance in sustainable agriculture and carbon dioxide fluxes", Advances in Agronomy, 101, 1-57
      DOI: 10.1016/s0065-2113(08)00801-8

    2006

    1996

    • Poulton, P. R.(1996) "Broadbalk Wheat Experiment", Global Change and Terrestrial Ecosystems, Report No. 7, GCTE Task 3.3.1, Soil Organic Matter Network (SOMNET): 1996 Model and Experimental Metadata (Smith P. , Smith J.U. and Powlson D.S. (eds) - GCTE Focus 3 Office, Wallingford, UK), 69-72

    1993

    • Hart, P. B. S. , Powlson, D. S. , Poulton, P. R. , Johnston, A. E. and Jenkinson, D. S.(1993) "The availability of the nitrogen in the crop residues of winter wheat to subsequent crops", Journal of Agricultural Science, 121, 355-362
      DOI: 10.1017/S0021859600085555

    1990

    • Jenkinson, D. S.(1990) "The turnover of organic carbon and nitrogen in soil", Philosophical Transactions of the Royal Society of London, Series B, 329, 361-368
      DOI: 10.1098/rstb.1990.0177

    1983

    • Dyke, G. V. , George, B. J. , Johnston, A. E. , Poulton, P. R. and Todd, A. D.(1983) "The Broadbalk wheat experiment 1968-78: yields and plant nutrients in crops grown continuously and in rotation", Rothamsted Experimental Station Report for 1982 , Part 2 , 5-44
      Get from eRAdoc: ResReport1982p2-5-44

    1969

    • Johnston, A. E. and Garner, H. V.(1969) "Broadbalk: Historical Introduction", Rothamsted Experimental Station Report for 1968 , Part 2 , 12-25
      Get from eRAdoc: ResReport1968p2-12-25
    • Johnston, A. E.(1969) "The soils of Broadbalk: Plant nutrients in Broadbalk soils", Rothamsted Experimental Station Report for 1968 , Part 2 , 93-115
      Get from eRAdoc: ResReport1968p2-93-115
    • Johnston, A. E.(1969) "The plant nutrients in crops grown on Broadbalk", Rothamsted Experimental Station Report for 1968 , Part 2 , 50-62
      Get from eRAdoc: ResReport1968p2-50-62
    • Johnson, C. G. , Lofty, J. R. and Cross, D. J.(1969) "Insect pests on Broadbalk", Rothamsted Experimental Station Report for 1968 , Part 2 , 141-156
      Get from eRAdoc: ResReport1968p2-145-160
    • Garner, H. V. and Dyke, G. V.(1969) "The Broadbalk Yields", Rothamsted Experimental Station Report for 1968 , Part 2 , 26-46; with references pp 49
      Get from eRAdoc: ResReport1968p2-26-46
    • Avery, B. W. and Bullock, P.(1969) "The soils of Broadbalk: Morphology and classification of Broadbalk soils", Rothamsted Experimental Station Report for 1968 , , 63-81 with references pp 112-115
      Get from eRAdoc: ResReport1968p2-63-81

    For further information and assistance, please contact the e-RA curators, Sarah Perryman and Margaret Glendining using the e-RA email address: era@rothamsted.ac.uk