Modélisation de la dynamique du carbone et de l’azote dans le système d’association légumineuses-céréales: Rôle fonctionnel de la symbiose rhizobienne dans le contrôle de la biodisponibilité du phosphore dans la rhizosphère

Abstract

Through field experimentations, this study aimed to assess the beneficial effect of the legume-cereal intercropping system in enhancing soil phosphorus availability for plant growth, grain yield and nitrogen (N) uptake in calcareous or alkaline P-deficient soil in Algeria agroecosystem. To address this aim, field experiments, using common bean (Phaseolus vulgaris L. cv. El Djadida) and cowpea (Vigna unguiculata L. cv Moh Wali) intercropped with maize (Zea mays L. cv. Filou and cv. ILT), either in pure stand or intercropping, were conducted in some experimental sites. However, all flow of carbon and nitrogen from the atmosphere to plants and soil were modeled under intercropping system by validation of MOMOS(Micro-Organisme et Matière Organique du Sol) model on CN data which are collected in these fields’ experiments. P availability in the rhizosphere was increased in both sole cropping and intercropping systems compared with fallow or sol bulk. It was highest in intercropping. The increase in P availability was associated with: (i) significant pH changes of the rhizosphere of cowpea in sole cropping and intercropping systems, with the rhizosphere acidification significantly higher in intercropping (-0.73 units) than in sole cropping (-0.42 units); (ii) significant increase in the rhizosphere pH of intercropped maize (+0.49 units) compared to fallow; (iii) increased soil respiration (C-CO2 from microbial and root activity) in intercropping compared with sole cropping and fallow; (iv) higher efficiency in utilization of the rhizobial symbiosis in intercropping than in sole cropped cowpea and common bean, with a significant correlation (r2=0.71) between common bean nodule growth and P availability in the rhizospher and (v) an enhancement of N uptake by shoot and seed of maize intercropped with common bean. While, CN modeling showed that in low P and N soil; growth of intercropped maize or common bean and the microbial transformations were positively correlated during crop cycle. Thus, the functional role plays by nodule for C and N exchange from the soil to the atmosphere (CO2) and from the atmosphere to the soil (N2). With cowpea-maize and common bean-maize intercropping, cowpea and common bean increased the P uptake, by increasing the P availability by some rhizosphérique mechanisms (protons (H+) release and nodule permeability). Overall, this study showed that intercropped legumes improved the plant biomass and grain yield of maize in an alkaline or calcareous P deficient soil.