DOI: 10.23637/rpg5-oayieldsperiod2-2
title: Dataset: Park Grass Hay Yields, Fertilizer and Lime Treatments 1903-1964

description: This dataset contains the yields of hay (t/ha), for both the 1st and 2nd cuts, harvested from Park Grass Hay Experiment since 1903-1964. Details of the fertilizer, lime treatments and harvest dates are also included. In 1903, "Design Period 2", started on Park Grass. The experiment was originally one plot per treatment since 1856, but in 1903, most plots (1-13 and 16) were split into two to test the effects of liming, as acidity had built up in the soil with fertilizer use. One half of each plot was limed with chalk (L) and the other half left un-limed (U). In 1920 the remaining plots (14, 15 and 17) were split in half also, to join the liming scheme. Three other plots (18, 19 and 20) were split in to three in 1920 to receive light lime (LL), heavy lime (HL) and un-limed (U). Yields are provided for all fertiliser treatment plots and sub-plots. Yields are expressed as t/ha at 100% dry matter. Variations in yield reflect the various fertilizer treatments and liming regimes, as well as the local weather and atmospheric inputs. This data set is followed by that for post-1965 data and so includes plot numbers ("subsequent plots"), and dates of introduction, from that later design-period to provide continuity between datasets. 

This 2nd version; In 2025 a new convention for plot ID format (new_plot_id) has been introduced that enables compatibility of plot names throughout the duration of the Park Grass Experiment datasets. This has been applied retrospectively to plots and more easily communicates plot changes over time and continuity between plots in the published data. It also aims to address the Excel date problem whereby a number of plot names that can be auto-converted to dates by Excel. The new conventions for plots split for fertilizer modifications uses '.' as the division separator. The new conventions for plots divided for new liming treatments uses '\' as the division separator. The traditional format is also kept in the dataset (plot_id). 

This version also includes a note about the sunny and shaded parts of the south end of plot 14 - whereby a comparison was done to establish the shading effects of a large oak tree in 1920 and from, 1924-1959. This dataset contains the averaged data of 'shaded' vs 'sunny' (the separate data is available from the e-RA database).
description: This experiment tests the effects of inorganic fertilizers, organic fertilizers and soil pH (which varies on sub-plots as a result of liming) on yields of hay. See Second Design Period 1903-1964 for detail. Until 1959, the yields were estimated by cutting and weighing the whole sub-plot produce. Since 1960, yields were estimated from strips cut from the centre of each plot with a forage harvester. In the dataset, the forage harvester weight is converted using an equation from Bowley et. al for 1960-1964, and both values are provided. See Additional Information below for conversion equations.

Since 1960, after the first cut in mid-June the remainder of each plot is 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 a forage harvester.
description: An Excel file, 02-rpg5_yields_1903-1964.xlsx, contains Park Grass fertilizer and lime treatments and the yields for the 1st and 2nd cuts. Frictionless CSV files are provided for users who prefer CSV over Excel files.
description: Hay yields have been recorded every year since the Park Grass experiment began, with the first harvest in 1856. Dried samples have also been kept since 1856 and these are preserved in the Rothamsted Sample Archive. 

<b>Change in harvesting method in 1960:</b>
There was a change in the harvest method in 1960 which has resulted in recorded yields of dry matter being larger than previous harvest method, as fewer losses occur. The previous harvest method to 1959 was estimated yield by weighing the produce from the whole field. Since 1960, the yield of a strip cut by the forage harvester at 100% dry matter (two per plot), weighed immediately in the field, is used for yield value for 1960-64 (and post-1965, see next dataset). The remainder of the plot is mown and made into hay in the usual way, continuing earlier management and ensuring the return of seed. A conversion equation for 1960-1964, to match pre-1960 yields, is Yield cut 1 = 0.2743 x (YF^1.663) (See references, Bowley et al (2017). 

<b>Example of new naming convention:</b>
Plot 4/1L (original name) is also described as 4.1\L (new naming convention - the .1 indicating the original whole plot 4 has been split to make plot 4.1 when a fertiliser modification was made to the original plot; the \L indicating that a liming treatment has been introduced on it).
description: Individual plot yields are derived from the PGHAYEQUIV dataset in the e-RA database and were checked with the published yields in the annual Rothamsted Yield Books. Park Grass data 1856- was entered to the e-RA database by Jackie Potts. In accordance with the Joint Code of Practice for Research at Rothamsted, data processing in e-RA follow rigorous standard operating procedures to ensure the quality and correctness of data collected in the field through to depositing in the e-RA database. To ensure quality control during data inputting, the data sets were typed on two separate occasions (double data entry). During the second typing (verification) the data values were compared with those typed on the earlier occasion, and any discrepancies were resolved before verification continued. This procedure also set out how to handle situations where the written records were illegible or ambiguous. This procedure avoided visual checking of data, which can be very inaccurate. Once the data were entered into e-RA, they were independently back-checked against the original data sheets. Park Grass was initiated to investigate the ways of improving the yield of hay by the application of inorganic fertilizers and organic manure. With time, the soil became more acidic and in 1903 plots had been halved and the effects of lime tested.

From 1965 a new liming regime was initiated with four sub-plots, three receiving lime to maintain soil pH (0-23cm depth) at pH 7, 6, and 5 on sub-plots a, b and c. Sub-plot d does not receive any lime. These later yields are available in the dataset 'Park Grass Hay Yields, Fertilizer and Lime Treatments 1965-2024' (and subsequent updates).

To convert these data 1903-1964 (and also the 1856-1902 dataset) 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).