Green manure and maize intercropping with reduced chemical N enhances productivity and carbon mitigation of farmland in arid areas

Keeping high productivity and low soil carbon emission (CE) while reducing chemical fertilizer is a significant challenge for crop production in developing modern agriculture. A field experiment was conducted to evaluate the effect of intercropping green manure with reduced N on maize productivity and carbon mitigation in northwestern China. The field experiment used a split-plot design with three replicates. Three cropping patterns were maize-common vetch intercropping (M/V), maize-rape intercropping (M/R), and sole maize (M). Two N fertilizer rates formed the subplots: the conventional N rate was reduced by 25% (N1: 270 kg ha-1) and the conventional N rate (N2: 360 kg ha-1). The compensation effect (TCE, %) was used to quantify the degree of recovery of intercropping green manure on maize grain yield (GY) under N reduction. It was shown by the results that the negative effect of N reduction on maize GY was compensated by intercropping green manure. Maize-common vetch intercropping integrated with N reduction (M/VN1) had a more substantial compensation ef-fect (TCE) with the planting years lengthening, and TCE was 1.0%, 0.9%, 4.1%, and 4.9% in 2018, 2019, 2020, and 2021, respectively. The CE of the cropping system was decreased by intercropping green manure compared to sole maize. The CE in the intercropping system was further decreased by N reduction, and the CE of M/RN1 and M/VN1 was decreased by 27.7% and 32.1%, respectively, compared to MN2 (i.e., the control). Finally, the CE of the intercropping system was decreased by M/VN1 by 6.5% compared to M/RN1 in 2019-2021. We used the ratio of net primary productivity to carbon emission (NPP/CE) to determine soil C sequestration (CS) potential. Intercropping green manure with N reduction in enhancing soil CS mainly occurred in the late growth period of maize. Over the four years of study, the ratios of NPP/CE for M/RN1 and M/VN1 were 23.3% and 32.9%, respectively, greater than that of MN2; also, it of M/VN1 was increased by 8.9% compared to M/RN1 in 2019-2021. M/VN1 had great potential for enhancing soil CS. Thus, adding green manure as an intercropping component in the maize cropping system while reducing chemical N fertilizer is a promising system to enhance maize productivity and carbon mitigation in the farmlands of arid areas.