The STICS intercrop model accurately reproduces interspecific interactions and yield in semi-arid West African cereal-legume intercropping systems

Cereal-legume intercropping offers potential for the sustainable intensification of annual cropping systems. Crop models can support the evaluation of agronomic and environmental benefits of intercropping. However, to be effective, they must capture interspecific interactions during the growing season, a challenging task in tropical systems where such models remain largely untested. This study assessed the ability of the STICS model to simulate cereal-cowpea intercropping productivity and the final outcomes of interspecific interactions occurring over the cropping season under tropical semi-arid conditions. Data from four experimental sites in West Africa, including sorghum, millet, and cowpea grown in sole cropping, were used for parameter calibration. STICS was evaluated using intercropping measurements. To analyse interspecific interactions in intercropping with contrasted sowing patterns, we adapted the partial Land Equivalent Ratio (pLER). Specifically, we corrected the pLER of each crop by dividing it by the ratio of the number of plants per m² in intercropping to the number of plants per m² in sole cropping (pLER cor.dens ). This adjustment allowed us to evaluate interactions at the plant level. Four situations were identified: i) cereal and legume pLER cor.dens < 1, indicating that competition outweighed complementarity, compensation, and cooperation or facilitation effects, i.e., productivity of both crops was reduced in intercropping, ii) cereal pLER cor.dens > 1 and legume pLER cor.dens < 1, indicating that the cereal suppressed legume growth, iii) cereal pLER cor.dens < 1 and legume pLER cor.dens > 1, indicating that legume suppressed cereal growth and iv) cereal and legume pLER cor.dens > 1, indicating that the productivity of both crops was enhanced by intercropping. STICS simulated cereal aboveground biomass and grain yield in intercropping with a higher model efficiency (Ef) than 0.48 and cowpea aboveground biomass with Ef = 0.31, but Ef < 0 for cowpea grain yield. The model simulated intercropping yields with low bias and was robust across agro-pedoclimatic conditions, but rRMSE was superior to 30%. In over 70% of irrigation × fertilisation × site combinations, STICS accurately simulated interspecific interactions, thanks to its accurate simulation of potential yields and water and N limitations. High observed soil moisture at the experimental sites limited the evaluation of model performance in simulating competition for water in intercropping. Despite room for improvement, the STICS intercrop model accurately reproduced cereal-cowpea intercropping yields and interspecific interactions in semi-arid tropical conditions. • STICS soil-crop model was calibrated using sole cereal and cowpea data and evaluated on intercropping. • STICS successfully reproduced dynamic interspecific interactions and their final result without intercropping-specific calibration. • The model accurately simulated intercropping yields in contrasting semi-arid conditions of West Africa. • STICS accurately simulated partial Land Equivalent Ratio of cereal-cowpea intercrops.