The Innovation Team of Improvement and Amelioration of Soil Fertility of the Institute of Agricultural Resources and Regional Planning (IARRP) of the Chinese Academy of Agricultural Sciences (CAAS), based on long-term field experiments on upland red soil, revealed the underlying mechanisms of fertilization management in regulating the soil nitrogen supply and loss pathways, providing theoretical support for optimizing farmland nitrogen fertilizer management. The relevant research results were published in Agriculture, Ecosystems & Environment.

Soil nitrogen supply is closely related to crop growth and yield. The depolymerization of soil organic nitrogen is the rate-limiting step controlling soil nitrogen transformation. In recent years, large amounts of studies have found that microbial nitrogen use efficiency plays an important role in soil nitrogen supply. Long-term fertilization changes soil physical and chemical properties, microbial community structure, thereby regulating microbial nitrogen use efficiency and related nitrogen transformation processes. However, the mechanisms of the soil nitrogen transformation processes in response to long-term fertilization management remain unclear.

Based on the long-term field experiment of upland red soil in Qiyang and Jinxian Observation Experimental Stations of National Soil Quality, this study investigated the mechanisms of differences in soil gross nitrogen mineralization, ammonium immobilization and nitrification rates in response to the application of chemical fertilizers and organic fertilizers using 15N and 18O isotope tracer technology.

The results showed that compared to the chemical fertilizer treatments, manure application increased gross nitrogen mineralization rate by 4.55-8.31 times, ammonium immobilization rate by 7.35-11.34 times, and the gross nitrification rate decreased by 38-55%. The application of organic manure alleviated the imbalance of soil and microbial carbon and nitrogen, increased the activity of nitrogen depolymerase, decreased microbial nitrogen use efficiency, and enhanced soil organic nitrogen mineralization. Organic fertilizer application increased ammonium immobilization by increasing microbial biomass and reducing the availability of ammonium, thereby decreasing gross nitrification rates.

Fig. 1 The pathways of organic fertilizers in regulating soil gross nitrogen mineralization, ammonium immobilization and nitrification rates. [Photo/IARRP]

Postdoctoral fellow Wang Jun of the IARRP is the first author, and professor Zhang Wenju is the corresponding author. The study was funded by the Ministry of Science and Technology Fundamental Resources Survey and the National Natural Science Foundation of China.

Paper link: https://doi.org/10.1016/j.agee.2023.108439