Long-term nitrogen management strategies based on straw return improve soil carbon and nitrogen fractions and nitrogen use efficiency of maize in the Tumochuan Plain Irrigation District

Wenbo Li¹Jiawei Qu¹Julin Gao^1*Xiaofang Yu^1*Daling Ma¹Shuping Hu¹Qinggeer Borjigin¹Kexin Lu²

• ¹Inner Mongolia Agricultural University, Hohhot, China
• ²Inner Mongolia Tongliao agricultural and Animal Husbandry Academy, Tongliao, China

Straw returned rational quantification of nitrogen fertilizer application play a critical role in regulating the relationship between the transformation of soil organic carbon and nitrogen availability, thereby facilitating crop yield enhancement, improving nitrogen use efficiency (NUE), and soil fertility improvement. However, the changes in soil carbon and nitrogen components under straw return combined with different nitrogen application conditions, as well as their contribution to crop yield and nitrogen efficiency, remain unclear. A three-year split-plot field experiment was conducted with deep plowing with straw return (DPR) and no straw return (RT) as main plots, and four nitrogen rates (300, 255, 210, and 0 kg ha⁻¹) as subplots. Compared to RT, DPR significantly improved soil nutrient contents and labile carbon and nitrogen fractions in the 0-40 cm soil layer. It also increased maize yield, NUE, and partial factor productivity of nitrogen (PFPN) by 17.28%, 18.24%, and 17.88%, respectively. Under DPR treatment, the linear-plus-plateau model predicted that the optimal nitrogen application rate could be reduced to 237.3 kg ha⁻¹, representing a significant 20.89% reduction compared to conventional nitrogen inputs. At this application level, soil carbon and nitrogen fractions and nitrogen use efficiency remained consistently high. Regarding contributions to yield and nitrogen efficiency, mineral nitrogen (MN), soil quality index (SQI), and dry matter accumulation (DMA) emerged as the most critical factors influencing yield, NUE, and PFPN. Their relative contributions to NUE were 9.39%, 8.96%, and 8.49%, and to PFPN were 9.31%, 9.18%, and 8.99%, respectively.Other soil components indirectly contributed to improved maize yield and nitrogen efficiency by stimulating microbial activity, promoting MN release, and enhancing soil fertility. In addition, straw return significantly increased soil nitrogen availability and maize yield by elevating the SQI and MN content. Even with a 15-20% reduction in nitrogen application, DPR effectively sustained soil carbon and nitrogen fractions, crop yield, and nitrogen use efficiency. These findings provide practical guidance and scientific support for optimizing nitrogen fertilizer management under long-term straw return practices, with strong implications for enhancing nitrogen use efficiency and soil fertility in high-input maize production systems.