Response of soil gross nitrogen mineralization to fertilization practices in China’s uplands

Improving soil nitrogen (N) supply capacity is recognized as a viable solution for sustaining cereal production for food security, since more than half of N absorbed by crops comes from the soil through the gross N mineralization (GNM) process. However, significant uncertainties exist regarding GNM patterns driven by commonly used fertilization practices in croplands. Based on soils collected from 13 long-term fertilization trials spanning over 30 years across China’s uplands by using the ¹⁵N dilution technique, we found that manure amendment led to the highest increase in GNM (1.9-9.7 folds), followed by straw return (0.8-4.7 folds) and chemical fertilizer application (0.07-3.9 folds), compared to the unfertilized treatment. Fertilization-induced GNM changes were primarily influenced by the initial soil pH in the chemical fertilizer and straw treatments, and by soil clay content in the manure treatment. Application of chemical fertilizer and straw in higher pH soils and manure in higher clayey soils had a greater promotion on GNM, mainly due to the enhanced soil properties (e.g., total dissolved N) and associated microbial attributes (e.g., N-acquiring enzyme activity, bacterial and fungal biomass). Manure amendment also facilitated GNM in low pH soils by promoting microbial attributes. These findings underscore the importance of differentiated fertilization managements at the district level to maximize soil N supply across China’s uplands, with prioritizing application of chemical fertilizer and straw in neutral and alkaline soils and manure in acidic and heavier texture soils. This knowledge is crucial for developing policies aimed at buttress food security and reduce soil N loss in China.