*3.1.4 N-fixation by legumes and transfer to associated non-legume*

Legumes are known to fix atmospheric nitrogen biologically. The biological nitrogen fixation (BNF) is a process where some bacteria convert atmospheric N2 into ammonia (NH3) and making it available to plants. In maize-legume intercropping system, both the crops acquire N from the common soil pool and compete and thus deficit of mineral N may occur in the rhizosphere which promotes legume to fix atmospheric N [48, 49]. Maize is an exhaustive crop and legumes are soil replenishing crops and decomposition of legumes residue improves soil fertility. In the soils with poor available nitrogen status, the biologically fixed nitrogen plays an important role. Under the situation of limited supply of nitrogenous fertilizer also intercropping legume and non-legume may a suitable option of nutrient management. Further, chemical N fertilizers are responsible for degradation of ecosystem in the form of nitrate pollution and legumes grown as intercrops help in environmental sustainability [50]. In maize-soybean intercropping system, soybean supplements nitrogen to cereal component [51]. Maize grown as forage in intercropping with legumes is known to improve quality parameters of forage like higher crude protein and mineral content and digestibility [48, 52]. Biologically fixed N by pigeon pea was transferred to associated maize and N content and uptake by maize was improved in maize-pigeon pea intercropping system [53]. The associated non-legume crop (maize) gets benefit of fixed N by legumes [1]. Thus, maize-legume intercropping system is beneficial in terms of N economy too. Leaf defoliation of legumes is known to increase productivity of maize–soybean intercropping system [22].
