Direct measurement of selected soil services in a drained agricultural field: Methodology development and case study in Saclay (France)

Over the last decade, many researchers around the world have realized the importance for society of the many services provided by soils, and a significant body of research has been devoted to estimating them using various types of proxies or relying on models. However, the field has suffered so far from a complete lack of actual measurements with which to evaluate available estimation methods. In this context, the key objective of the present research was to obtain, for the first time, direct measurements of several services provided by soils. The experimental site at which the research was carried out is an agricultural field located southwest of Paris (France), which presents the unique advantage that is it artificially drained, and therefore allows accurate mass balances to be computed over time for rain water, nutrients, and herbicides applied to the soil. A detailed methodology is presented to extract, from these data, quantitative measurements of 3 provisioning services (supply of water to nearby stream, provision of food by supplying, respectively, water and nitrogen to wheat crop), and 3 regulating services (flood mitigation, and filtration of, respectively, nutrients and herbicides). The results obtained with this methodology, and the relative significance of the different services are discussed. In particular, it is shown that, given the industrial-type of agriculture practiced at the site and its heavy reliance on fertilizers, the service related to the supply of nitrogen to the crops by the soil is not marginal, accounting for 22% of the total nitrogen consumption by the wheat. The availability of quantitative measures of selected soil services now paves the way for a detailed assessment of the various estimation methods currently in use, and the development of improved approaches.