Trees and tree row herbaceous vegetation impact soil organisms distribution in a market gardening agroforestry plot

National audienceThe herbaceous vegetation in agroforestry tree rows is a poorly studied potential trophic resource and habitat for soil organisms. This could enhance nutrients turnover (Porazinska et al., 2003), and thus be beneficial for the crop. We studied soil macrofauna density, soil microbial biomass and soil organic carbon in a 22 year-old organic market gardening plot with walnut trees, located in the South of France. We hypothesized that 1) the herbaceous strip impacts soil organism development and that 2) soil organism development also varies with tree management. Three treatments were studied: no trees in the herbaceous strip, lightlypruned trees and heavily-pruned trees. Three positions were sampled: in the herbaceous strip, at 1 m from the herbaceous strip and at 2 m from the herbaceous strip. Sampling was carried out in April, June and November 2018. The first results for the Spring and Summer seasons demonstrate that the heavy pruning treatment presented the highest microbial biomass, and soil carbon content was higher in treatments with trees. However, macrofauna density did not vary according to the pruning treatment. Macrofauna density was increased in the herbaceous strip compared to the crop alley in all treatments, but not microbial biomass. Our first results suggested different impacts of trees and herbaceous vegetation: a stronger effect of the herbaceous vegetation for macrofauna density, and a stronger effect of the pruning of the tree for microbial biomass