Performance of Legume Crops under Different Agroforestry Systems: A Comprehensive Review

Grain legumes and agroforestry are each promoted as routes to sustainable intensification, but the agronomic consequences of combining them remain inadequately synthesised. This review compares the grain yield, biological nitrogen fixation, soil response and economic return of ten major food legumes, namely chickpea, pigeonpea, cowpea, mungbean, urdbean, lentil, field pea, soybean, groundnut and faba bean, grown under six agroforestry models, namely agrisilviculture, alley cropping, agrihorticulture, silvopastoral systems, boundary plantation and multistrata systems. Peer-reviewed literature published from 2010 to 2025, together with landmark earlier studies, was retrieved from Scopus, Web of Science, ScienceDirect and Google Scholar and screened against defined inclusion criteria. Qualifying studies were arranged in a legume by model matrix and in a nitrogen and soil matrix and were interpreted qualitatively within the competition and facilitation framework of tree-crop interaction. Legume performance was determined more consistently by the interaction between understorey radiation and soil water supply than by the land use system studied. Facilitation predominated on humid and fertile soils, where trees added nitrogen and moderated the microclimate, whereas in semi-arid environments below-ground competition for water cause yield loss. Soybean, groundnut and the cool-season pulses were the most shade-sensitive species, while cowpea, pigeonpea and several mungbean genotypes maintained yield under moderate shade. Reported fixation ranged from approximately 20 to 400 kg N ha^-1 and declined when canopy shading limited the supply of photosynthate to the nodules. Legume-inclusive agroforestry raised soil organic carbon and ecosystem-service delivery in most reported comparisons. Across the humid to semi-arid gradient, the evidence identifies widely spaced agrisilviculture and boundary plantations carrying deciduous or regularly pruned nitrogen-fixing trees, sown to plastic warm-season legumes such as cowpea, mungbean and pigeonpea, as the configuration most reliably matched to grain legume production. Future research should replace comparisons between system labels with factorial genotype by tree by environment experiments.