The impact of straw return and other factors on soil nitrogen: A meta-analysis

【Objective】 Straw return not only improves soil fertility but also soil structure and soil health. In this paper we systematically analyze the effects of different biotic and abiotic factors on effect of straw return on soil nitrogen. 【Method】 The meta-analysis was based on 42 papers indexed by CNKI, Web of Science and Science of Direct, in where there were 314 pairs of data that compared nitrogen change in soils with and without straw return. Other factors considered include straw types, soil conditions prior to straw return, straw return methods, straw return amount, nitrogen fertilization, years after inception of straw return. 【Result】 Regardless of straw types, straw return increased total soil nitrogen content. Straw return promoted nitrogen accumulation in sandy and loam soil more than in clay soils. In alkaline soils, straw return improved nitrogen fixation. The efficacy of straw return in increasing soil nitrogen decreased with the increase in carbon-nitrogen ratio of organic matter in soil. Compared to soil without straw return, straw return combined with plowing, rotary tillage, and no-tillage increased soil total nitrogen content by 9.11%, 7.84% and 5.34%, respectively. Straw return also increased soil nitrogen accumulation, but the increase was not significantly dependent on straw amount. Applying less than 150 kg/hm2 of straw improved soil nitrogen fixation at the same level as applying 150-250 kg/hm2 of straw. When nitrogen fertilization exceeded 250 kg/hm2, straw return significantly increased soil nitrogen accumulation. The length of period over which straw return was implemented did not affect soil nitrogen significantly, and the effect of long-term straw return application (>10 a) and short-term straw return application (1-4 a) on soil nitrogen change was approximately the same. 【Conclusion】 Coarse alkaline soils with low C/N ratio facilitate straw decomposition and nitrogen mineralization. Our results show that combining straw return with tillage and rational nitrogen fertilization was effective in improving soil nitrogen accumulation in soils where straw return application had been implemented for less than 10 years.