Part of experiment rpg5

Harvesting methods

The plots were originally cut by scythe, then by horse-drawn and then tractor-drawn mowers. The mowing maching was first used for the first cut in 1901, though it had been used for the second cut since 1881. The plots were cut each year for hay, usually in June, and a second cut taken in the autumn since 1875. A second cut was not taken every year, and not from every plot each year, if there was insufficient herbage to sample. No second cut taken 1856-1874, 1876, 1884, 1885, 1887, 1899, 1911, 1914, 1921, 1924, 1933 or 2003. In 1903-1917, the second cut was taken from the whole plot, not the Limed and Unlimed halves. The regrowth after the first cut was grazed by sheep 1856-1872, except for 1866, 1870, and 1873 and 1874, when the regrowth was mown but not removed from the plots.

Yields were originally estimated by weighing the produce from the whole plot, either as hay (1st harvest) or green crop (2nd harvest), and dry matter determined. Since 1960, yields of dry matter have been estimated from strips cut with a forage harvester. For the 1960-2020 period, a forage harvester with a 1.1-m cut width was used and the cut grass weight was determined with an in-field balance. Since 2021, a new machine has been in use, the 'Amazone Forage Harvester'. This has a 1.5-m cut width and the machine is fitted with a bespoke weighing balance which weighs the cut as it goes. For the first cut the remainder of each plot is still mown and made into hay, continuing earlier management and ensuring return of seed. For the second cut, the whole of each plot is cut with the forage harvester.

Recorded yields of dry matter since 1960 are now larger than the 1856-1959 period as fewer losses occur when yields are based on the weight of the grass immediately as it is cut. The following correction factor should be used for post-1960 data for cut 1 to give yield values equivalent to pre-1960 values:

Y_{cut 1} = 0.2743 x (Y_F ^1.662 ) (Bowley et al, 2017)

where Y_F = yield collected by forage harvester, t/ha. The correction factor was obtained from the relationship between yields for hay and forage harvested cuts (r² = 0.90) for a selection of plots for 1959 and 1992-1994. For more details, refer to Bowley et al, 2017 (see Key References below). (To convert the data 1856-1959 to align with the data from 1960-present, the reverse formula for Bowley's conversion equation is Yield = EXP((1/1.662)*LN(old yield/0.2743)) where LN() is the natural log function i.e loge() and EXP is the exponential function i.e. EXP(a)=ea (S. Clark, March 2025).

Key References