Maize and legume intercropping enhanced crop growth and soil carbon and nutrient cycling through regulating soil enzyme activities

Maize intercropped with leguminous green manure (LGM) has been proven as a sustainable plantation practice for enhancing crop yield and soil fertility. However, a comprehensive understanding of how intercropped legumes coordinate the above- and below-ground performance during maize growth under low to high N application remains elusive. This study aimed to investigate the effects of biological C and N input on soil fertility and maize growth by regulating soil enzyme activities in maize/LGM intercropping systems. A three-year field trial was conducted in northwestern China, where maize was intercropped with two LGMs, namely common vetch and pea, under no N (N0, 0 kg ha- 1) and conventional N (N330, 330 kg ha- 1) applications. The grain yield of intercropped maize ranged from 10.54 to 11.08 t ha- 1, representing a significant increase of 6.6-12.1 % compared to monoculture maize in the N0 treatment. Nitrogen application substantially increased maize grain yield by 39.2-52.0 % across cropping systems relative to the N0 treatments, while minor differences were observed in maize yield between cropping systems in the N330 treatments. Compared with monoculture maize, intercropped with LGMs increased C input by 16.7-79.2 % at maize V9 stage and 81.1-140.3 % at the R6 stage. The biological N fixation of intercropped LGMs was 62.7-89.5 kg ha- 1 and 8.0-12.8 kg ha- 1 in the N0 and N330 treatments, respectively. Biological C and N input greatly facilitated soil enzyme activities and the associated nutrient cycling, consequently improving soil fertility. Soil organic matter and total N in the intercropping systems significantly increased by 4.4-14.3 % relative to monoculture across maize growth stages, irrespective of N levels. Furthermore, increased soil fertility was closely associated with nutrient stoichiometry, which in turn facilitated maize nutrient uptake and shoot recovery growth in the intercropping systems. Overall, these findings highlight that increased biological C and N input to belowground enhances soil C and nutrient cycling by regulating the involved enzyme activities, which in turn improves maize nutrient uptake and growth, forming a coordinated loop of C and nutrient flow in the maize and legume intercropping systems. Maize intercropped with LGMs is a sustainable practice that improves soil fertility and promotes maize growth by augmenting biological C and N input.