Organic matter content rather than farming practices modulates microbial activities in vineyard soils

Abstract

Soil functioning is a growing concern in intensively-managed agricultural landscapes such as vineyards. Mechanical disturbance of the soil and pesticide use have deleterious impact on microbial activity, which is a key parameter for organic matter decomposition and nutrient cycling. This study aims to assess the response of soil microbial activities under different farming systems (organic and conventional systems) and inter-rows management (grassy or tilled inter-rows). We selected 18 fields in the southwest of France, supporting tilled and grassy inter-rows (alternating treatment) - 9 fields were managed organically and 9 were managed conventionally. We assessed extracellular enzymatic activities relative to C, N, P acquisition and Microresp™, which allows to measure catabolic capacities of soil microbial communities. Our results showed that organic systems had a higher soil organic matter (SOM) content than conventional ones. At the inter-row scale, grassy inter-rows of organic vineyards differed from tilled inter-rows in catabolic capacities of microbial communities; with overall a higher complexity of C-substrates respired by microbial communities. Furthermore, N- and P-related enzymes were positively correlated to SOM and soil pH across sites and managements, suggesting that increasing SOM may positively impact nutrient recycling and notably NO₃^-. Altogether, our results pointed out the importance of soil organic matter content on soil microbial functioning in vineyards as well as the possible benefit of organic matter inputs on nutrient recycling and nitrogen directly available in the vineyard.