This paper reports spatial and temporal changes at the regional level in soil organic carbon (SOC) using a soil-test database. A total of 23 329 SOC test values recorded between 1990 and 2004 by certified commercial laboratories and collected in a mountainous French region (Franche-Comte´) were integrated in a database. Results show a strong trend in organic carbon content, mainly related to elevation. A large loss in SOC was observed over the survey period. This loss correlated with baseline SOC content with greater loss from soils with higher carbon content. This loss is likely to be due to both changes in land use from permanent grassland to cultivation and to an increase in temperature during the survey period. Our study demonstrates that past soil-test results which were not originally intended for monitoring can provide an alternative method for detecting changes in SOC.

No abstract

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).