Effect of organic amendments on yield-scaled NO emissions from winter wheat-summer maize cropping systems in Northwest China.

The effect of dairy manure amendments to agricultural soil on the yield-scaled nitrous oxide (NO) emissions remains unclear. We hypothesize that an optimum ratio of dairy manure to synthetic fertilizers leads to large nitrogen use efficiency (NUE) and small yield-scaled NO emissions. The aims of this study were to (1) quantify the variations in the crop yields and NO emissions from winter wheat-summer maize cropping systems in Northwest China, (2) determine the responses of the NUE and yield-scaled NO emission to the ratio of organic materials to synthetic fertilizers, and (3) evaluate the relationship between the NUE and yield-scaled NO emissions. Field measurements were conducted within long- and short-term fertilization experiments between the years of 2014 and 2016. Treatments included synthetic fertilizers, synthetic fertilizers plus crop residues, and synthetic fertilizers plus dairy manure at both sites. The annual grain yields and NO emissions varied from 13.3 to 18.0 Mg ha and from 1.3 to 3.6 kg N ha, respectively, across the treatments. The yield-scaled NO emissions related negatively to the NUE, suggesting that agronomic aims of improving NUE are an effective approach to mitigate NO emissions. The ratio of organic materials to synthetic fertilizers was not a significant limit on the NUE and yield-scaled NO emissions. We conclude that organic amendments appeared to play a minor influence on the promotion of the NUE and NO mitigation.