Distribution of soil organic carbon and nitrogen under reduced nitrogen application in the Guanzhong plain of China

Background The problems of soil quality degradation and environmental pollution caused by excessive use of nitrogen fertilizer seriously affect sustainable development of agriculture. Aims We investigated the effects of reduced nitrogen application with simultaneous full straw return on carbon input, aggregate size distribution, aggregate-associated organic carbon and total nitrogen (TN), soil organic carbon (SOC) stock, SOC fractions, and crop yield. Methods A long-term field experiment was performed in the dryland region of Guanzhong. The study involved three nitrogen fertilizer (NF) amounts: 337.5 (conventional NF, CNF), 286.4 (15%NF reduction, 15%RNF), and 236.3 (30%NF reduction, 30%RNF) kg N ha(-1) y(-1) with full straw return. Results Compared with CNF, 30%RNF increased the content of soil organic carbon by 5.7% and increased maize yield by 13.1%, under straw return conditions. The 30%RNF + straw application treatment promoted the formation of large macro-aggregates more effectively than CNF application. The 30%RNF + straw treatment significantly increased SOC by 10.6% and 4.7%, respectively, in large and small macroaggregates relative to conventional NF. Moreover, the 30%RNF + straw treatment resulted in a significant increase in the SOC content in the density fractions of mineral soil organic matter (mSOM) for both small and large macro-aggregates. This treatment also resulted in a significant increase in the content of TN in the mSOM and density fractions of particulate matter that had coarse and fine intra-aggregates of the large macro-aggregates. Conclusion Full straw return with reduced nitrogen (N) application could be a promising option to improve the structure of soil aggregates, soil organic carbon, and nitrogen sequestration.