DOI: 10.23637/rex4-ptestsoil7423-01
title: Dataset: Exhaustion Land Experiment P test soil P 1974-2023

description: This dataset contains topsoil (0-23 cm) Olsen phosphorus (P) and total P data for the "P Test" plots (plots 1, 3, 5, 7 and 9) of the Exhaustion Land Experiment, 1974-2023. The plots were divided into four sub-plots testing four rates of P fertilizer 1986-1992. Maintenance applications of P were then applied to all plots except the P0 from 2000 onwards. Olsen-P is a widely used indicator of plant-available soil P. 

The residual effects of fertilizer and manures applied in 1876-1901, and the additional P applied in 1986-1992 have resulted in a wide range of plant-available P in the soil. Soil was not sampled every year. This is the soil data reported by Haefele et al. (2025); crop yields and P uptake are published as a separate dataset.
description: The experiment was established in 1856 with four large plots, a fifth was added in 1876 and each was divided to create 10 plots (1-10) in 1876, each receiving a different fertilizer or manure treatment until 1901. No fertilizer or manure was applied 1902-1939. Basal nitrogen (N) fertilizer was applied to all plots 1940-1974; no other fertilizer or manure was applied. No crop was grown in 1975. In 1976 the plots were divided into four sub-plots, and four N fertilizer treatments were applied 1976-1985. 

In 1986 half the plots (1, 3, 5, 7 and 9) received four different P treatments, in the P build-up phase. These plots are known as the "P Test" plots. No P was applied 1993-1999. From 2000 onwards maintenance P fertilizer was applied to all plots, except the Nil (P0). 

**Fertilizer P treatments** (kg P ha<sup>-1</sup> yr<sup>-1</sup>, as triple superphosphate):
 - 1986-1992: the plots were divided into four sub-plots given four rates of P: P0=0, P1=44, P2=87 and P3=131 kg P 
 - 1993-1999: no P applied. Shown as P0 (P0), P0 (P1), P0 (P2), P0 (P3) in the dataset

**Maintenance P** (kg P ha<sup>-1</sup> yr<sup>-1</sup>, as triple superphosphate):
 - 2000-2008: 20 kg P to all plots except to the previous P0 treatment (61.5 kg P applied in error in 2000). Shown as P0 (P0), P (P1), P (P2), P (P3) in the dataset
 - 2009-2015: 15 kg P to all plots except to the previous P0 treatment. Shown as P0 (P0), P (P1), P (P2), P (P3) in the dataset
 - 2016-2023: 15 kg P to all plots except to the previous P1 and P0 treatment . Shown as P0 (P0), P0 (P1), P (P2), P (P3) in the dataset 

Refer to Exhaustion Land Experiment plans and fertilizer treatments, Phase IV and V for more details (see Related Documents).
description: **Soil sampling**:
The soil on each plot was sampled in the autumn after harvest of the crop, usually every two or three years, occasionally with a longer interval. Each sample comprised 16-20 individual cores taken with a 2.5 cm semi-cylindrical gouge auger from the 0 to 23 cm horizon and bulked to make a single sample per plot, before any fertilizer was applied. 

**Olsen P content**:
Olsen P was measured by the method of Olsen et al. (1954). Air-dried, sieved &lt;2 mm soil was extracted with 0.5 <i>M</i> NaCO<sub>3</sub> at pH 8.5, using a modified method of Murphy and Riley (1962). The extract was analysed on a continuous segmented colorimetric flow analyser (Skalar).
Olsen P concentration is given as mg P kg<sup>-1</sup>, because 5 g of soil was weighed for analysis. This differs from advisory work, where concentration is reported as mg P L<sup>-1</sup>, because a volume of 10mL of soil is used. Both methods give similar but not identical results (both being on a parts-per-million basis). 

**Total soil P**:
Soil total P concentration was measured in soil sampled in 1974 and 2006 by aqua regia digestion (Crosland et al., 2008), the archived 1974 samples were re-analysed by this method in 2008. 

**References**:
- Crosland, A.R., Zhao, F.J., McGrath, S.P., Lane, P.W., 2008. Comparison of aqua regia digestion with sodium carbonate fusion for the determination of total phosphorus in soils by inductively coupled plasma atomic emission spectroscopy (ICP). Commun. Soil Sci. Plant Anal. 1357-1368. 
- Murphy, J., Riley, J.P., 1962. A modified single solution method for the determination of
phosphate in natural waters. Anal. Chim. Acta 27, 3-36.
- Olsen S.R., Cole C.V., Watanabe F.S., Dean L.A. (1954) Estimation of available phosphorus in soils by extraction with sodium bicarbonate. USDA Circular 939, US Gov. Print. Office, Washington, D.C.
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description: Individual plot soil P values were taken from Rothamsted Research archives. Agronomic information (fertilizer application etc) was taken from Rothamsted Experimental Station Annual Reports. The P content is derived from analysis made by the Analytical Chemistry Unit, Rothamsted Research, Harpenden. 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. 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.