Modelling the functional role of the microorganisms in the daily exchanges of carbon and nitrogen in cereals –legumes intercropping system

Abstract

The modelling of the continuous exchange of carbon (C) and nitrogen (N) published previously in the literature is little focused on the functional role of micro-organisms. Concerning plant covers, this modeling was mostly performed in sole crop systems and poorly investigated under field conditions at the farm scale, in which evidence was lacking for intercropping. This work focus on the mechanistic modelling approaches based on the ecological functioning of microbial biomass (MB), in order to quantify the daily exchange of C and N between plant organs, micro-organisms, rhizobial symbionts, soil compartments and atmosphere. The MOMOS model was validated on C and N data collected from common bean (Phaseolus vulgaris L. cv. El Djadida)/ maize (Zea mays L. cv. Filou) intercropping system. Experiment was performed with two field sites chosen with farmers to represent two contrasted phosphorus (P)-soil conditions. Results show that all C and N exchanges were successfully predicted at 5% significance, they are often varied depending on the phenological stages, and so more during the flowering stage. The optimized C allocations from photosynthesis to root were contributed to increase both grain yield and N grain for intercropped maize. C and N stocks in common bean nodules were lower in intercropping than in sole crop. This was associated with the decrease of total N2 fixation by intercropped common bean, in particular in high P-soil. However, the optimized rate of N fixation was greater in intercropping than in sole cropping system where P is limited in the soil. The most of C loss from soil was found mainly transferred by microorganisms to the atmosphere. It was significantly minimized in intercropped plots, in order to improve C use efficiency by living microorganism. These results uncover the strong link between N and C stocks, confirming the robustness of MOMOS equations that were newly formulated and checked in this thesis. The present agroecological modelling demonstrated the functional role of microbial biomass, in the growth of the mixed crop and symbiosis interaction, in order to predict better the daily C and N exchange flows between plant organs, soil compartments and atmosphere.