DOI: 10.23637/rpg5-pgsoilcn-01
title: Dataset: Park Grass Soil Organic Carbon and Total Nitrogen 1856-2023

description: This dataset consists of the soil organic carbon (SOC), nitrogen (N), and soil weight, of individual plots of the Park Grass experiment, 1876-2023, and estimated values for when the experiment began in 1856. SOC and N were measured six times between 1876 and 2023. Soil weight was measured in 1876, 1959 and 2011/12. Data is given for the 0-23 cm soil depth. Not all plots were sampled on each occasion. Also included are details of the fertilizer and lime treatments applied. 

<b>Estimated starting values</b> for when the experiment began in 1856, before the fertilizer and lime treatments were started were 3.1% SOC and 0.26% N. 

On some plots, given ammonium salts but no lime, the soil became highly acidified and mats of undecomposed plant material have built up. These are indicated in the dataset. 

These soil data are discussed in Poulton et al. (2026).
description: <b> Soil sampling. </b> Soil was sampled in 1876, 1923, 1959, 2002, 2017 and 2023 to measure SOC and total N. All plots were sampled in 1876 with an open-ended metal box which was 30.5 x 30.5 cm square by 22.9 cm deep. Just three samples were taken from each plot, as this method was disruptive to grassland soil structure. Since the 1920s soils have mostly been sampled with semi-cylindrical gouge augers, typically, 15-20 cores are taken from each plot or sub-plot with a 2 cm diameter auger; cores are bulked to give one sample per plot/sub-plot. Samples are not taken within 1 m of the plot edges. In some cases, the top 23 cm layer is divided into 0 - 7.6, 7.6 - 15.2 and 15.2 - 22.9 cm layers and occasionally sub-soils (23 - 46 cm, 46 - 69 cm and 69 - 91 cm) are sampled (no sub-soil data is shown in this dataset). All data is expressed on a 0 - 23cm basis; however some are weighted means from soils sampled 0 - 7.6 cm, 7.6 - 22.9 cm and some are arithmetic means of 0 - 7. 6cm, 7.6 - 15.2 cm, 15.2 - 22.9 cm samples.

Soils were air-dried, ground and sieved to &lt; 2 mm and routinely analysed for pH in water (published as a separate dataset), exchangeable cations and plant-available P (published as a separate dataset). A sub-sample was more finely ground, &lt; 44 mesh, for organic C, or Total C and inorganic C, Total N, and occasionally for Total P.

Archived soils from 1876 and 1923 have been sub-sampled and re-analysed using current analytical techniques in the last 20 years. The analytical data given here is from these later re-analyses. 

<b> Soil organic carbon (SOC)</b> was determined by the Tinsley (1950) method described by Bremner and Jenkinson (1960); previously by Walkley and Black (1934) with a factor to make it equivalent to Tinsley. Since the 1990s, organic C has been calculated as Total C minus Inorganic C. Inorganic C was determined using a manual manometer and calcimeter, and more recently by a carbon flexible solid sample analyser (PrimacsSNC-100-IC-E Carbon/Nitrogen analyzer, Skalar Analytical BV, Breda, Netherlands). Total C has been determined by combustion analysis (CN928 Analyser, Leco Corporation, St Joseph, Michigan, USA). Soil C is determined on air-dried, finely ground soil (44 mesh). 

<b> Soil total nitrogen (N)</b> was measured by Kjeldahl (1883) until the early 1990s and since then by combustion (CN928 Analyser, Leco Corporation, St Joseph, Michigan, USA) on air-dried, finely ground soil (44 mesh). 

<b> Weight of dried sieved soil, 0-23 cm </b> Soil weight was measured in 1876, 1959 and 2011/12. A known volume of soil was sampled, and it was therefore possible to calculate the weight of the soil in each horizon. In 1876 the soil was sampled with an open-ended metal box, 30.5 cm x 30.5 cm by 22.9 cm deep. In 1959 the soil was sampled by semi-cylindrical augers of known volume. Soil weights were calculated in 2011/2 after sampling with a pneumatic sampler. Three cores were taken from selected sub-plots with a 4.85 cm diameter auger, 0-23 cm. Soil weights in 2011/12 include mat where present, but mat and soil weights were also calculated separately (data not shown in this dataset).
description: 1. <b>A FAIR data Excel file</b> data-PG-soilCN-01.xlsx, contains Park Grass SOC and total N data for 1856-2023. Frictionless CSV files are also provided.

2. <b>A Simple Excel file</b> simple-data-PG-soilCN-01, that provides the data in a readily readable tabular format, containing separate sheets:
- <b>Soil total N</b> Data table containing soil total nitrogen data for Park Grass plots and treatments, 0-23 cm deep, 1876-2023 and estimated value for 1856.
- <b>Soil organic C</b> Data table containing soil organic carbon data for Park Grass plots and treatments, 0-23 cm deep, 1876-2023 and estimated value for 1856.
- <b>Soil weight</b> Data table containing soil weight data for Park Grass plots and treatments, 0-23 cm deep, 1876- 2023.
description: <b>References</b>

Bremner, J. M. and Jenkinson, D. S. (1960) <i>Determination of organic carbon in soil. I. Oxidation by dichromate of organic matter in soil and plant materials.</i>, Journal of Soil Science, 11, 394-402 https://doi.org/10.1111/j.1365-2389.1960.tb01093.x 

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.
description: This dataset is from measurements led by Andy Gregory, Andy Macdonald, Paul Poulton, and previous scientists, and latterly analysed by the Analytical Chemistry Unit, Rothamsted Research, Harpenden, see list of contributors. The data have been collated into this FAIR dataset by Margaret Glendining and checked by Sarah Perryman. Information on methods of soil sampling and methods of analysis are taken from Poulton et al, 2026. The Analytical Chemistry Unit follows the Joint Code of Practice (JCoPR) and participates in European Quality Assurance programmes. All performance is strictly monitored using certified external standards alongside in-house standard materials. Standards and check samples are monitored and recorded. <b> New plot ids. </b>
From 2025, an additional plot identification number, "new_plot_id" 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.