Agroecological practices as drivers of soil biodiversity and multifunctionality for sustainable vegetable crop production (Madagascar, Highlands) – INTENSOL

Soil biodiversity drives the ecological intensification of agriculture by supporting multiple soil functions, including nutrient recycling, maintaining soil structure, and regulating pests and pathogens. However, studies assessing how soil biodiversity influences soil functions often (i) fail to capture the complexity of real agroecosystems, particularly in terms of farming practices, multi-trophic biodiversity, and soil multifunctionality. Additionally, they (ii) rarely explore the mechanisms through which soil organisms impact soil functions and (iii) inadequately incorporate farmers' perceptions and knowledge. In Madagascar, there is significant interest in soil ecological intensification due to the convergence of severe soil degradation, limited access to chemical fertilizers, and pervasive malnutrition challenges. To encourage food diversification in regions where rice dominates both cultivation and diets, several recent agroecology initiatives have focused on peri-urban market gardening. On the periphery of Antananarivo (Highlands), this project will examine how agroecological practices influence the relationship between soil biodiversity, soil multifunctionality, and vegetable crop production. (1) First, we will investigate how farmers associate agroecological practices with soil functions and soil biodiversity, and evaluate whether biophysical soil indicators align with farmers’ assessments of soil functions. Using a participatory approach that combines farmer interviews, field visits, educational activities on soil functions, and biophysical soil characterization on selected plots, we will identify and compare the complementarities between farmers' perspectives and scientific indicators. (2) Second, through a field experiment, we will evaluate how combinations of farming practices—such as the addition of organic matter, reduced tillage, and traditional biopesticides (“Ady Gasy”)—affect the relationship between soil biodiversity, soil multifunctionality, and vegetable crop production. Employing a multidisciplinary approach that incorporates both scientific and farmer-derived indicators of soil functionality, we will analyze changes in multitrophic biodiversity (bacteria, protists, fungi, nematodes, microarthropods, and macrofauna) and their associated soil functions, including nutrient recycling, soil structure maintenance, and pest/pathogen regulation. This experiment will test for synergies or antagonistic effects among farming practices and establish a methodological framework for studying soil multifunctionality in agroecosystems. (3) Finally, in a mesocosm experiment, we will investigate the pore-scale mechanisms driving the incorporation of organic inputs into the soil micro-food web and their effects on nitrogen (N) cycling and crop growth. Specifically, we will examine how the degree of pore water saturation, which relates to important farming practices for market-gardening, such as irrigation and organic matter application, influences the relative dominance of the bacterial (aquatic) versus fungal (non-aquatic) pathways in the soil food web. This spatially focused approach to soil microhabitats is novel in soil food web ecology, and our work will serve as a methodological reference for linking trophic interactions, microscale soil functions, and plant growth. Overall, the INTENSOL project will adopt multi- and transdisciplinary approaches to (i) integrate farmers' and scientific knowledge into a unified framework for evaluating soil functions, (ii) provide field-based evidence on how practical combinations of farming practices influence soil biodiversity, soil multifunctionality, and vegetable crop growth, and (iii) lay the groundwork for a mechanistic understanding of the microscale processes that underpin the biological recycling of nutrients.