Legume/Maize Intercropping and N Application for Improved Yield, Quality, Water and N Utilization for Forage Production

Legume/maize intercropping has been practiced in many countries as a sustainable cropping system, but the effects of intercropping legumes with maize together with N application rates on biomass yield, quality, water-use efficiency (WUE), and nitrogen use efficiency (NUE) are limited under arid conditions in Northwest China. Field experiments were carried out in arid areas of Northwest China from 2019 to 2020 with three planting patterns (LM: Dolichos lablab (Lablab purpureus L.)/silage maize (Zea mays L.) intercropping; FM: Fodder soybean (Glycine max L.)/silage maize intercropping; M: silage maize monoculture) and four N application levels (N1: 0 kg N ha(-1); N2: 120 kg N ha(-1); N3: 240 N kg ha(-1); N4: 360 N kg ha(-1)). The results showed that nitrogen fertilizer had a significant (p < 0.01) effect on total yield, WUE, and various nutrient parameters and the interaction between planting mode and nitrogen fertilizer had no significant effect on the above indicators, but had a significant (p < 0.01) effect on NUE. Compared with N1, the N3 and N4 treatments significantly increased fresh and hay yield, crude protein yield, crude protein concentration, and crude fat concentration of maize, legumes, and the whole silage system, and decreased the concentration of neutral detergent fiber (NDF) and acid detergent fiber (ADF). In comparison with N1, the 2-year average total biomass yield of N3 and N4 increased by 60.38% and 56.45%, respectively, and the total crude protein yield increased by 106.71% and 100.00%, respectively. High N input treatments (N3 and N4) significantly increased WUEB (the WUE of legume and maize biomass), N concentration, N uptake, and NUE than N1, and the 2-year average NUE of N3 was 59.52% greater than that of N4. The results also show that LM and FM increased crude protein concentration and decreased NDF and ADF concentration compared with M, and the forage quality of LM was greater than that of FM. In contrast with M, LM and FM increased biomass yield by 3.70% and 1.72%, crude protein yield by 32.05% and 22.82%, and WUEB by 10.49% and 6.02%, respectively. Application of 240 kg N ha(-1) in the Dolichos lablab-maize intercropping systems produced better dry biomass yield with increased forage qualities than other treatments, but the economic analysis is needed before making a recommendation.