Effects of long-term tillage on soil nitrogen transformation, nitrogen fractions, and wheat yield

The response of soil nitrogen (N) transformation processes and N supply capacity to tillage practices is crucial for reducing soil N loss and promoting sustainable agricultural development. However, the comprehensive research and driving mechanism of how long-term positioning tillage methods affect wheat yield through soil nitrogen transformation, soil nitrogen supply capacity, and soil nitrogen loss are still unclear. A long-term field experiment was initiated in 2007 (lasting 16 years) with four tillage treatments: perennial plowing tillage (PT), perennial rotary tillage (RT), perennial strip rotary tillage (ST), and subsoiling every two years combined with strip rotary tillage (STS). In 2022, the changes of soil N transformation intensity, soil N-transforming enzyme activity, NH₃ volatilization, N₂O emission and soil N fractions in wheat fields were measured at different wheat growth stages. Additionally, ¹⁵N isotope tracer technology was used to explore the N absorption and utilization of plants under different tillage practices. Our results demonstrated that, compared to PT, RT, and ST, the STS treatment significantly increased the intensity of soil nitrogen fixation, ammonification and nitrification at different growth stages of wheat. It also increased soil urease and protease activities while reducing denitrification intensity, nitrate reductase, and nitrite reductase activities, consequently decreasing cumulative N₂O emissions. Furthermore, the STS treatment significantly increased soil total nitrogen, particulate organic nitrogen, soluble organic nitrogen, microbial biomass nitrogen, ammonium nitrogen, and nitrate nitrogen contents. The ¹⁵N tracer technology showed that STS treatment could promote the absorption of N fertilizer and reduce the loss of N fertilizer. In addition, STS significantly increased the grain yield by 8.62%-20.44% compared with other treatments, with better yield stability. Through partial least squares method, it was found that STS significantly promotes N conversion and N pool composition, indirectly promotes N absorption, thereby promoting wheat yield increase, while suppressing cumulative N₂O emissions and reducing N loss. Overall, the STS treatment enhanced soil N transformation, reduced soil N loss, provided sufficient N support for plant growth, promoted N uptake, and achieved the highest grain yield. Therefore, STS represents a sustainable tillage method for reducing soil N loss and improving crop yield.