Abstract:

Intercropping green manure optimizes the nitrogen (N) rate in high-yield maize production. However, the effectof cropping pattern on soil organic carbon (SOC) accumulation is unclear. This study investigated the interactioneffects between the N rate and green manure intercropping on the SOC biochemical composition of a maize fieldin an oasis region of China using amino sugars, lignin phenols, and phospholipid fatty acids (PLFA) as bio-markers. Without green manure crops, decreasing N rate from 360 kg ha 1 (conventional) to 270 kg ha-1(reduced) for 7 years decreased SOC and total N stocks in the 0.4 m upper soil by 20%-24%. In contrast, withgreen manure intercropping, these reductions were of negligible magnitude. Decreases in SOC and total N underreduced N fertilization in areas without green manure were linked to microbial necromass C (MNC) depletion. Inplots with green manure, this loss was compensated for by MNC and lignin accumulation. The ratio betweenfungal- and bacterial-derived MNC was evidently lower in the plots without green manure but was maintained inplots with green manure under reduced N fertilization compared with conventional N fertilization. Reduced Ndid not affect microbial biomass or the fungal-to-bacterial PLFA ratio, but decreased the ratio between C- to N-acquiring enzyme activities and N availability. Intercropping green manure increased soil microbial biomass, theratio of fungal- to bacterial-derived PLFAs, and the ratio of C- to N-acquisition enzyme activities, and buffered thedecrease in N availability caused by reduced N. These results indicate that in N fertilizer-reduced plots, decreasesin soil MNC without green manure were ascribed to increased mineralization of microbial (particularly fungal)debris because of intense N limitation, whereas the maintenance of MNC with green manure was associated withincreased microbial (particularly fungal) debris input and reduced mineralization because of alleviated microbialN limitation. We demonstrated the link between soil MNC accumulation and N status in croplands, showing thatN rate can be optimized by intercropping green manure in maize production, which increases SOC formation byreducing N loss and inputting high-quality organic components.