DOI: 10.23637/rpg5-pgyields19652024-1
title: Dataset: Park Grass Yields and Fertilizer Treatments 1965-2024

description: In 1965, a new design, "Third Design Period", was introduced on Park Grass for most plots, with a new soil liming regime, having four sub-plots per each plot to provide soil at (a) pH 7, (b) pH 6, (c) pH 5 and (d) un-limed. This dataset contains the annual yields of hay (t/ha), for both the 1st and 2nd cuts, harvested from Park Grass Hay Experiment from 1965 to 2024 inclusive. Details of the fertilizer, lime treatments and harvest dates are also included. Yields are provided for all fertiliser treatment plots and sub-plots (except for plots 5, and 6c & 6d, which are used for micro-plot experiments). 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 new dataset also introduces an additional plot identification number, "new_plot_id" (as well as adding another years data for 2024, to the previous 1965-2023 dataset). This new plot id number uses a new naming convention assigned retrospectively to all plots since the start of the experiment in 1856. It is intended to show the provenance of the treatments of the plots using ' \ ' and '.' to indicate significant changes, where ' \ ' indicates a liming change and '.' indicates a plot-split for a fertilizer modification. For example, original plot number id., 7\1a now also has the new plot id., 7.1\L\a, where 7.1 indicates it has been split, for a new fertilizer treatment, and \L\a indicates the changes in liming it has undergone (where L a indicates a limed half pre-1964 and a indicating lime to pH 7 from 1965. See Technical information for a further explanation (on this dataset webpage).

<b>NB. the change in harvest method in 1960 means recorded yields of dry matter are larger than previously as fewer losses occur. See Additional Information (on this dataset webpage) for a conversion factor to use for post-1960 data for cut 1 to give yield values equivalent to pre-1960 values and see Methods for the harvesting details (on this dataset webpage).</b>

Plot 12 and 15 did not join this new liming scheme until 1976.
description: This experiment tests the effects of inorganic fertilizers, organic fertilizers and soil pH (which varies on sub-plots as a result of liming which is applied to counteract the acidifying effects of fertilizers) on yields of hay. See 'Design Period 3' 1965- for detail. 

<b>Harvesting method.</b>
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. The yields are estimated from strips cut from the centre of each plot with a forage harvester (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. 

<b>Plot changes.</b>
<b>The original scheme whole plots: </b> whole plots initiated in 1856 (plots 1-13), 1858 (plots 14-17), 1865 (plot 18) and 1872 (plots 19 & 20). Since 1990, plots 9 and 14 have been divided into 9-1 & 9-2 and 14-1 & 14-2. Since 1995, plot 13 has been split into 13-1 & 13-2. Since 1996, plot 2 has been split into 2-1 & 2-2. Plot 7 was divided into 7-1 and 7-2 in 2013 and P withheld from 7-1.. Refer to references and plans for complete details of plot split histories. Note; in data file plot-splits are shown with a hyphen '-' whereas in the plans they are indicated by a slash '/' e.g. plot 9-1 is equivalent to 9/1.

<b>Sub-plots:</b> In 1903 most whole plots (not plot 12, not plots 14 & 17 until 1920, and not plot 15 until 1976) were split in half with the southern half receiving lime, being limed (L) and unlimed (U). Plots 18, 18 and 20 were not included in this liming scheme and instead were split in 1920 to sub-plots 1 unlimed (U), 2 high lime (HL) and 3 low lime (LL). 

<b>Sub-sub plots:</b> In 1965 limed and unlimed half plots were split again halved on their North-South axis to give the 4 plots labelled a, b, c & d. Plot 12 was not included in the a, b, c, d set up until 1976, between 1965-1975 it was two half-plots 12ab and 12cd neither of which received lime. Plot 15 1965-1975 was two halves 15ab (limed) and 15cd (unlimed), it became a, b, c, d sub-plots in 1976. Plots 18/2, 19/1-3 and 20/1-3 were not included in the liming scheme in 1965. Plots 5 and 6c & d are microplots and not used in the yields experiments.
description: An Excel file, rpg5_yields_1965-2024_01.xlsx, contains Park Grass fertilizer and lime treatments and the yields for the 1st and 2nd cuts. Some columns on the crop_data sheet (and associated rows on the fields_metadata sheet) are highlighted in colour to enable easier recognition of key columns - i.e. plot ids, treatments, harvest years and yields. Frictionless CSV files are provided for users who prefer CSV over Excel files. Also a figure using a subset of the data for illustrative purposes.
description: <b>Plot changes over time and new naming convention since 2025.</b>
Hay yields have been recorded every year since the Park Grass experiment began, with the first harvest in 1856. The first significant change came in 1903 when a new limed/unlimed (L and U) scheme was introduced (Design period 2). In 2025, to enable more easy use of the plot names through time, and to ensure Excel does not change plot names to dates due to the traditional plot names that tend to use use '/' and '-' , a new naming convention is being introduced (proposed by R. Ostler) to more easily communicate plot changes over time and continuity between plots in the published data. This also aims to address the Excel date problem whereby we have a number of plot names that can be auto-converted to dates by Excel. 
 
A. '-' and '/' have been used to indicate plot divisions as new treatments are added. These symbols can cause problems with Excel date autoformatting and are not used consistently. They are replaced with '.' and ' \ ' based on the rules below. 

B. Some traditional plot names do not use a separator to indicate plot divisions. For example 8U, or 8a. Consistent use of separators would help communicate the underlying historical plot structure. 

C. The new conventions for plots divided for fertilizer modifications: 
For example, plot 7 has been divided with the new halves traditionally labelled 7/1 and 7/2 or 7-1 and 7-2. The new plot id uses '.' as the division separator to become 7.1 and 7.2.
a. This avoids potential for Excel date conversions
b. This aligns with naming on Broadbalk for strips 2.1 and 2.2 
c. This avoids different plot division hierarchies and preserves this part of the plot as a 'main plot' name based on the fertiliser treatment. 

D. The new conventions for plots divided for new liming treatments: 
Plots were first divided into 'L' and 'U' plots (noting exceptions for plots 12 and 18-20) then further divided in to 'a', 'b', 'c', 'd'. By using a backslash to indicate each division. e.g. plot 8U becomes 8\U becomes plots 8\U\c and 8\U\d; plot 20/1 becomes 20\1.
a. This avoids potential for Excel date conversions for plots 18-20.
b. This communicates the provenance of the plot, for example 8\U\d (traditional name 8d) can automatically be seen to be a division of plot 8\U. 

The combination of . and \ preserves the historical treatment hierarchy. i.e 8\U\d and 7.1\U\d can be seen to exist within the same treatment hierarchy with respect to to liming even though 7 has undergone an additional plot division to introduce a new fertiliser treatment.
description: Up to 2018 data, individual plot yields are derived from the PGHAYEQUIV dataset in the e-RA database, originally entered by Jackie Potts,then by Gill tuck, then Margaret Glendining & Sarah Perryman, and were checked with the published yields in the annual Rothamsted Yield Books. Since 2019 individual plot yields have been provided by C. Hall to S. Clark, checked by A. Gregory and then to the e-RA curators. 

This Frictionless dataset of combined yield and treatment data was compiled by S. Perryman and checked by M. Glendining May 2025. The new plot naming conventions were proposed by Richard Ostler. Nathalie Castells packages and mints the FAIR datasets and DOIs.

We acknowledge the many and significant essential contributions by many over the years, from Farm staff, such as T. Hall, previous LTE managers, such as P. Poulton, and technical staff such as C. Hall. 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.

<b> Conversion Factor for post 1959 data</b>
The change in harvest method in 1960 means recorded yields of dry matter are larger than previously as fewer losses occur. The previous harvest method estimated yield by weighing the produce from the whole field. See reference by Bowley et al (2017) which suggests the following conversion factor to use for post-1960 data for cut 1 to give yield values equivalent to pre-1960 values:

Ycut 1 = 0.2743 x (YF 1.662 ) 

where YF = 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.

(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).

NB. Dried samples of cut hay have been kept since 1856 and these are preserved in the Rothamsted Sample Archive.