S13 - Session O1 - Apple trees enhance the soil microbial activity in a garden-orchard system

Authors: Toky Ramananjatovo *, Juliette Peugeot, Pascale Guillermin, Etienne Chantoiseau, Mickael Delaire, Gerhard Buck-Sorlin, René Guénon, Patrice Cannavo

In horticulture, fertilization practices need to be reconsidered to limit their environmental impacts. Associating vegetables with fruit trees could be very promising as trees can enhance soil microbial activity and improve soil fertility via leaf litterfall and root turnover. This study aims at evaluating the effects of 20-year-old apple trees on soil quality in an apple tree-vegetables intercropping system. From September 2019 to August 2021, we performed measurements either under an apple tree row or on vegetable beds situated at 1.5, 3 m and 5 m from the apple tree row. Litterfall and soil organic matter (SOM) were quantified, and the soil microbial activity as well as its biodegradation capacity characterized by measuring: decomposition rates of apple tree leaf litter and crop residues, N mineralization, soil CO 2 fluxes and basal (BAS) and glucose-induced soil potential respiration (SIR). Litterfall of apple trees enriched the soil surface in organic matter from 70 g.kg -1 under tree row to 30 at 5 m. In the vegetable beds, the decomposition rate of the crop residues was significantly faster near the trees. We also observed that net N mineralization rate was up to twice higher at 1.5 m than at 5 m from the trees. Soil CO 2 fluxes were not significantly different among vegetable beds but should be further investigated. Under controlled conditions, we observed a decreasing gradient of BAS from the tree row to 5 m. Furthermore, soil in the tree row was more responsive to glucose induction than soil in vegetable beds. These results suggest that soil microbial activity was enhanced near the apple trees due to the enrichment in SOM by litterfall and probably by root exudates.