The Broadbalk experiment is one of the oldest continuous agronomic experiments in the world. Started by Lawes and Gilbert in the autumn of 1843, winter wheat has been sown and harvested on all or part of the field every year since then. The original aim of the experiment was to test the effects of various combinations of inorganic fertilizers (supplying the elements N, P, K, Na and Mg) and different organic manures on the yield of winter wheat; a control strip has received no fertilizer or organic manures since 1843. For the first few years these treatments varied a little, but in 1852 a scheme was established that has continued, with some modifications, until today.
The first experimental crop of wheat was sown on Broadbalk in 1843 and harvested in 1844. The aim of the experiment was to test the effect of different organic manures and inorganic fertilizers on the yield of winter wheat. For the first few years the treatments varied somewhat but in 1852 a permanent scheme was established which has continued, with minor modifications, to today.
The experiment has had three main phases:
1. 1843-1925. The first experimental crop of wheat was harvested in 1844 after a rotation of turnips (with FYM, 1839), barley (1840), peas (1841), wheat (1842) and oats (1843). The last four crops did not receive any fertilizer or manure. Winter wheat was grown continuously, apart from occasional fallowing to control weeds. 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, 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. See Broadbalk plan 1852-1925 (pdf); Broadbalk cropping 1844-1925 (pdf)
2. 1926-1967. The experiment was sub-divided into five 'Sections' (I - V) in 1926, crossing the treatment strips at right angles. These were bare fallowed sequentially to control weeds. Fallowing was mainly in a five year rotation of fallow with four successive crops of wheat. In 1955 Section I was divided into two; IA received herbicides as required and was no longer fallowed, IB continued in the five year cycle. In 1955 Section V was divided into two; VB received a single application of lime, VA did not. In 1963 Section VB was no longer fallowed and received herbicides as required, while VA continued in the five year fallowing cycle. See Broadbalk plan 1926-1967 (pdf); Broadbalk cropping 1926-1967 (pdf)
3. 1968 onwards. 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 (indicated as plot 'S' in the extracted data, eg Plot 9S, see Austin et al, 1993). 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, currently oats, forage maize, wheat, wheat, wheat. 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. See Broadbalk plan 1996-2017 (pdf); Broadbalk cropping since 1968 (pdf) and Broadbalk today (pdf).
The complexity of changes undergone by the Broadbalk experiment is spatial and temporal as illustrated by this example: Broadbalk timeline. It first consisted of single plots stretching the length of the field (Figure 3a), these were split into five sections in 1926 (I-V), to allow sequential fallowing to control weeds (Figure 3b) and subsequently divided to make 10 sections (numbered 0-9) in 1968 (Figure 3c), to allow the introduction of rotations on some of the sections.
Lawes and Gilbert installed a tile drain at the centre of each treatment strip and used these to collect and measure the nutrients in the water that leached through the soil. After 150 years many of these drains had collapsed and 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.
Sulphur (S) has been added, by default, as part of the potassium sulphate, magnesium sulphate, Kieserite, FYM and ammonium sulphate applications. S has not been applied to plot 14 since 2001.
From harvest year 2018 a new rotation of wheat > wheat > oats > wheat > beans has been introduced on the rotational sections (sections 2, 3, 4, 5 and 7), replacing the current rotation. See Broadbalk today (pdf) Please contact the e-RA curators for more details.
For more details, refer to the Rothamsted Guide to the Classical Experiments 2006 pages 8-18 and to the Key References listed below.
Broadbalk cropping and variety details:
The following data can be extracted using the e-RA Data Extraction Tool. Preview sets of data are also available.
Grain and straw yields are recorded each year. Other data collected include observations of weeds, pests and diseases and the results of chemical analyses of crops and soils. Physical samples of crops and soils have been preserved in the Rothamsted Sample Archive. For more details please contact the e-RA Curators.
With thanks to Paul Poulton for help with compiling the text and plans.