A global meta-analysis of soil nitrogen-cycling variables under no-tillage as compared to conventional tillage

Background and aims

As the core management practice of conservation agriculture, no-tillage (NT) is critical for stimulating soil nutrient cycling and sustaining crop productivity on farmland. However, our comprehensive understanding of nitrogen cycling is limited by contradictory results on nitrogen loss and the absence of a global quantitative assessment of nitrogen transformation processes and genes under NT. Therefore, this study aims to explore the impact of NT on soil nitrogen-cycling variables on a global scale.

Methods

A global meta-analysis with 304 observations from 60 publications was conducted on the effects of NT on soil nitrogen transformation rate, nitrogen-cycling gene abundances, and nitrogen pools.

Results

NT significantly increased soil net mineralization rate, ammonia-oxidizing bacteria gene abundance, total nitrogen, and ammonium nitrogen by 18.2%, 20.3%, 12.5%, and 17.4%, respectively, but it significantly reduced nitrogenase reductase gene abundance. Further investigation revealed that climatic conditions, soil properties, and agronomic practices at the experimental sites affect changes in soil nitrogen-cycling variables induced by NT. We found that NT-induced changes in the nitrogen transformation rate and the abundance of genes involved in the denitrification process were positively correlated with the mean annual temperature and aridity index, respectively. In addition, the combination of sustainable agronomic management practices with NT, such as straw return, crop rotation, and lower nitrogen fertilizer application, positively affects soil nitrogen cycling processes.

Conclusions

Overall, these results provide insights into understanding how NT affects soil nitrogen cycling and highlight the importance of rational agronomic management practices in stimulating soil nitrogen cycling under NT.