Enhancement joint fertilization efficacy of straw and nitrogen fertilizer on soil quality and seedcotton yield for sustainable cotton farming

Straw return with optimizing nitrogen fertilizer is an important way to achieve sustainable cotton farming. However, quantitative analysis of joint fertilization efficacy (JFE) of straw return and nitrogen fertilizer on soil quality and seedcotton yield remains uncertain. Herein, based on a 7-year field experiment, we evaluated the dynamic characteristics of JFE of straw return and nitrogen rates (75, 150 and 300 kg N ha⁻¹, denote as N75, N150 and N300, respectively) on soil quality index (JFE-SQI) and seedcotton yield (JFE-Y) in a cotton–wheat​ cropping system of East China. The results showed that straw return with moderate nitrogen rate (i.e.N150) improved soil quality by reducing bulk density, increasing soil carbon and nitrogen sequestration, promoting nutrient availability, stimulating microbial growth and enhancing soil enzyme activities, thereby improving seedcotton yield and its stability. Straw return with N150 could also achieve higher JFE-SQI and JFE-Y synergistically. Meanwhile, JFE-SQI and JFE-Y at N150 had a synergistic effect (JFE > 10%) in the first 5 year while a summing effect (−10% $\le$ JFE $\le$ 10%) from the sixth year. And the highest JFE-Y could be reached when moderate JFE-SQI was achieved, indicating that there was a nitrogen-driven tradeoff between JFE-SQI and JFE-Y. Moreover, Climatic factor exerted a significant contribution to seedcotton yield and JFE-Y. In conclusion, reasonable straw return and nitrogen fertilizer management strategy is an effective way to realize sustainable cotton planting under the global climate change.