Influence of the management and spatial arrangement of agroforestry systems on nitrogen recycling: a meta-ecosystem modeling approach

They can increase agricultural production, reduce soil erosion, conserve biodiversity, improve carbon sequestration, mitigate greenhouse gas emissions, and improve soil fertility. The different types of SAF vary in their plant diversity and structure, in space or time and derive their benefits from ecological interactions between their different “subunits” (trees, annual crops, perennial crops, meadows, spontaneous vegetation...).

Objectives

The spatial arrangement of SAF subunits, their plant composition and associated practices (ploughing, recycling of residues, etc...), determine the way in which they interact and affect ecological processes. Given the important role played by nitrogen in the productivity and sustainability of SAF, it is essential to be able to evaluate how the spatial arrangement of the subunits, their relative proportions, as well as the practices carried out there, can affect the recycling of this nutrient within SAF as well as the ecosystem services linked to it: plant production (fiber and food), and support (availability and conservation of nitrogen).

Since carrying out field experiments is costly in resources and requires long growth periods due to the perennial component of SAF, a meta-ecosystem model will be constructed. It will describe the flows and stocks of nitrogen within each of the subunits of a SAF as well as the flows connecting these subunits. It will take into account their spatial organization (arrangement, geometry and size), their plant composition and the agricultural practices carried out there. This model will enable the study of a particular SAF: the instrumented experimental alley-cropping site “DIAMS” (Mauguio, Hérault, Occitanie, France).

This multidisciplinary approach is innovative because it lies between ecological modeling and agronomic modeling. It allows us to focus on the roles of agricultural practices and spatial organization on the dynamics of nitrogen flows and stocks within the meta-ecosystem.

Approaches

A synthesis of the literature will be realized to help define a typology of SAF in their greatest diversity in order to identify and characterize the subunits of the different types of SAF with a view to constructing a generic model: possible spatial configurations, plant compositions and their associated biodiversity, soil types and associated soil functions, agricultural practices.

This typology will allow the determination of compartments, flows, as well as their mathematical expressions in the model. Parameters related to the spatial arrangement of the SAF, such as the relative areas of the subunits, will make it possible to determine the overlapping surfaces between them.
New data acquired in situ on the DIAMs instrumented experimental site will complement those already available to configure the model. The biomasses and plant productions of the different subunits of the SAF, as well as the mineral and organic nitrogen contents of the soil will be measured at different depths. Nitrogen isotope tracing will make it possible to evaluate transfer fluxes between SAF subunits.

Participants

INRAE resarch units

• AGROECOSYSTEM Department
  • ECO&SOLS Joint Research Unit - Functional Ecology and Biogeochemistry of Soils and Agrosystems
  • MISTEA Joint Research Unit - Computer mathematics and statistics for the environment and agronomy
  • ABSYS Joint Research Unit – Biodiversified Agrosystems
• IEES - Institute of ecology and environmental sciences of Paris - National Center for Scientific Research