Soil functions

Lead organisation: Agrocampus Ouest-INRA UMR SAS (Soil Agronomy Spatialization)

WP3 focuses on soil functions (i) which are controlled directly or indirectly by soil biodiversity (WP2) and (ii) which impact on soil ecosystem services such as agroecosystem productivity or GHG (WP4). Crop production is regulated by soil physical properties (soil structure governing root penetration, soil water status and soil aeration), by nutrient availability (SOM cycling, mineral and organic fertilization) and by pest control. GHG are related to nutrient cycling (C and N mineralisation, N20 emission) and impacted by soil physical properties (soil structure, aeration).
In WP3, we aim to assess the contribution of biological processes to (1) soil structure (soil aggregation) (2) soil water dynamics (infiltration, water storage, runoff, erosion) (3) soil organic matter (quantity, quality, availability), (4) nutrient cycling (nitrogen dynamics), (5) the filtering role of soil against pesticides (Glyphosate) and NO3 leaching, and (6) pest regulation.

Task 3.1. Soil structure (physical stability and support)
Soil physical structure will be assessed by taking into account the aggregation processes and in particular biological process. Firstly, biogenic structures will be described and quantified in the soil profile according to the description of soil structure patterns (Piron et al, submitted). At a selection of sites and treatments, soil structure will be characterized by a micromorphological description of macropores, classified according to their shape, size and origin, using image analysis on soil thin sections (Hubert et al., 2007). The physical stability will be assessed through the measurement of soil structural stability (Marinissen, 1994, Le Bissonnais, 1996, Bottinelli et al 2010).

Task 3.2. Water regulation
The capacity of soil to regulate water movement will be assessed by characterizing soil water retention and infiltration. Water retention curves will be measured on suction tables at five hydric potentials; hydraulic conductivity curves K(h) will be measured using two techniques: Minidisc Infiltrometer (DECAGON) at 3 water potentials in near saturated conditions, and Beerkan method at saturation. These data are already available for some of the sites. Available soil water content for crop will be estimated. The overall contribution to runoff and erosion will be studied in a specific experimental device (Kerguéhennec Transfer) and supplemented by rainfall simulations, at those sites where runoff and erosion is a relevant process (French sites only).

Task 3.3. Soil organic matter characterisation (nutrient cycling-buffering)
Soil will be sampled at different depths. Soil organic C will be analysed, together with soil bulk density to assess changes in soil C stocks (sequestration) with time and depth. SOM will be characterized by elementary analysis (C, N, C/N) and physical characterisation by granulometric fractionation (Balesdent et al., 1991).

Task 3.4. Nutrient cycling
Changes in mineral N (NO3 and NH4+) in the soil profile at different depths are monitored under 3 different tillage systems and organic anc conventional farming at the Lelystad site in the Netherlands. Data will be available to the project.

Task 3.5. Soil filtering (regulation of water quality)
Monitoring of pesticides losses will be realised on the experimental design Kerguéhennec Transfer, in relation to runoff experiment. If possible the same will be done in the drainage water of the Westmaas site in NL.

Task 3.6. Pest regulation
It will be assessed through the nematode community structure (see WP2). Our hypothesis is that tillage systems impact differently on nematode communities and that conventional tillage increases the development of phytoparasite nematodes as well as their dispersion. Data on nematode functional groups and changes with time are already available for the Lelystad site (since 2009).