The responses of soil organic carbon and total nitrogen to chemical nitrogen fertilizers reduction base on a meta-analysis

Soil organic carbon (SOC), total nitrogen (TN), and their ratio (C:N) play important roles in preserving soil fertility, and their values are closely related to fertilizer use. However, the overall trend and magnitude of changes in SOC, TN and C:N in response to chemical nitrogen fertilizers reduction remain inconclusive. Here, the meta-analysis conducted comparisons at 48 sites covering various cropping system, soil type, and climatic regions of China to investigate the responses of SOC, TN and C:N to chemical nitrogen fertilizers reduction. The results showed that chemical nitrogen fertilizers reduction decreased SOC by 2.76 +/- 0.3% and TN by 4.19 +/- 0.8%, and increased the C:N by 6.11 +/- 0.9% across all the database. Specifically, the reduction of chemical nitrogen without adding organic nitrogen fertilizers would reduce SOC and TN by 3.83% and 11.46% respectively, while they increased SOC and TN by 4.92% and 8.33% respectively with organic fertilizers supplement, suggesting that organic fertilizers could cover the loss of SOC, TN induced by chemical nitrogen fertilizers reduction. Medium magnitude (20-30%) of chemical nitrogen fertilizers reduction enhanced SOC by 6.9%, while high magnitude (>= 30%) and total (100%) of chemical nitrogen fertilizers reduction significantly decreased SOC by 3.10% and 7.26% respectively. Moreover, SOC showed a negative response to nitrogen fertilizers reduction at short-term duration (1-2 years), while the results converted under medium-long-termThis system analysis fills the gap on the effects of fertilizer reduction on soil organic carbon and nitrogen at the national scale, and provides technical foundation for the action of reducing fertilizer application while increase efficiency.

Automated summary

The reduction of chemical nitrogen fertilizers has both positive and negative effects on soil organic carbon, total nitrogen, and their ratio. The addition of organic fertilizers can compensate for the loss of organic carbon and total nitrogen caused by the reduction of chemical nitrogen fertilizers. Medium reduction of chemical nitrogen fertilizers increases soil organic carbon, while high reduction and total reduction significantly decrease it. In the short term, soil organic carbon shows a negative response to nitrogen fertilizers reduction, but it turns positive in the medium to long term.