Adaptive evaluation for agricultural sustainability of different fertilizer management options for a green manure-maize rotation system: Impacts on crop yield, soil biochemical properties and organic carbon fractions.

Green manure planting can reduce the intensity of soil use, while improving farmland productivity in double-cropping systems. However, only few studies have focused on the impacts of green manure application under different fertilization management options on succeeding crop yield and soil organic carbon (SOC) process. A three-year field experiment was conducted with a winter smooth vetch-summer maize cropping system to evaluate the effects of green manure with different chemical fertilizers on soil physiochemical properties, SOC fraction, enzyme activities and maize yield. Total eight treatments were compared including different combinations of green manure and chemical fertilizers (i.e., nitrogen and phosphorus fertilizers) in the smooth vetch phase and maize phase. The results showed that compared to the control, green manure incorporation increased the soil moisture, total nitrogen, total phosphorus, basal respiration, SOC and its labile fractions, and enzyme activities, especially for the treatments of green manure with fertilization. However, the soil pH and bulk density decreased due to green manure application. Maize yield increased 34 %-53 % after green manure application, and was found to be significantly and positively correlated with soil carbon process (P < 0.05). Moreover, SOC and its labile fractions, and total nitrogen were observed as the main drivers of the maize yield. Variation partition analysis demonstrated that soil biochemical properties and their interaction with green manure by fertilization caused variations in SOC fractions. Further, structural equation models indicated that both balanced fertilization practices had positive effects on maize yield and soil carbon process via changes in SOC fractions and C cycling-related enzyme activities, respectively. In addition, the amount balance of chemical fertilizer positively impacted the soil carbon process by regulating SOC fractions through enzyme activities. These findings provide important guidance for applying optimal fertilization management in the green manure phase to improve succeeding crop yield and soil quality as well as to mitigate the adverse impacts of chemical fertilizers. The study will be equally illuminating for other green manure-crop rotation systems.
Competing Interests: Declaration of competing interest The authors declared that they have no conflicts of interest to this work. We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.
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