Soil phosphorus monitoring at the regional level by means of a soil test database

• Published in: Soil use and management 2008-06, Vol.24 (2), p.131-138
• Main Authors: Lemercier, B, Gaudin, L, Walter, C, Aurousseau, P, Arrouays, D, Schvartz, C, Saby, N.P.A, Follain, S, Abrassart, J
• Format: Article
• Language: English
• Subjects: Agricultural sciences; Agronomy. Soil science and plant productions; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Life Sciences; Phosphorus; phosphorus balance; Soil science; Soil study; soil test database; spatial variability; temporal change
• ISSN: 0266-0032; 1475-2743
• DOI: 10.1111/j.1475-2743.2008.00146.x

The practice of applying large amounts of P to agricultural land over several previous decades, particularly in regions with intensive livestock production, has resulted in P accumulation in soils with an increased risk of P losses into water bodies and thus of eutrophication. This work is aimed at analyzing the spatiotemporal changes in extractable soil P content at the regional level by means of a soil test database and then comparing results with independent data from agricultural censuses. A total of 228 079 soil P-test values [Dyer method: 1:5 soil-citric acid solution (20 g/L) ratio] generated between 1980 and 2003 by certified commercial laboratories in Brittany (northwestern France) were integrated into a database. Changes in P were analysed by considering four 4-6 year periods between 1980 and 2003 using cumulative frequencies and summary statistics performed on raw soil test values. Then data were aggregated into discrete entities (canton: administrative entities) and summary statistics, linear regression and spatial distribution were carried out. P balances were measured for the same entities taken from the agricultural censuses of 1979, 1988 and 2000. Over the entire study period, a marked spatial variability was observed with higher P content in the western part of Brittany, as well as a systematic increase in median P content with lower amplitude over the past decade. The mean cantonal soil P surplus accumulated over 24 years amounted to 763 kg P/ha of usable agricultural land. Similar P balances sometimes gave rise to widely different increases in P. Cumulative balances were positively correlated with an increase in soil P (r² = 0.34).