How manure amendment counters no-tillage yield reduction in winter wheat: enhanced nitrogen components and soil enzyme activity.

Introduction: No-tillage (NT) effectively reduces soil erosion, enhances water retention, and promotes carbon sequestration, yet it often leads to yield reduction. The application of manure can mitigate the yield decline caused by NT. Therefore, combining NT with manure represents a key strategy for achieving sustainable agriculture. This study aimed to evaluate the effects of organic fertilizer application on soil physicochemical properties in long-term NT farmland, and reveal the regulatory associations of manure on crop yield in such systems. Methods: A split-plot design was employed, with tillage practices (CT and NT) as the main plots and fertilization treatments as sub-plots. The fertilization treatments included: no fertilizer (CK), mineral nitrogen (N), mineral phosphorus (P), manure-only (M); mineral N and P (NP); and combined N, P, and manure (MNP). Results: Compared with CT, NT significantly increased soil carbon fractions (SOC, and MBC by 19.09%, and 14.95%, respectively) and nitrogen fractions (AN and NN by 35.48% and 67.82%, respectively), as well as BD (increased by 11.83%), but decreased soil enzyme activities (CBH and NAG by 9.40% and 9.09%, respectively). In contrast, the combined application of manure increased soil carbon/nitrogen fractions, enzyme activities while effectively reducing soil BD and pH. Specifically, compared with the NP, the MNP treatment increased SOC, TN, AP, AN, CBH, and NAG by 31.25%, 23.67%, 65.35%, 28.48%, 37.33%, and 30.79%, respectively. Under the MNP, yield increased by 9.84% (CT) and 13.40% (NT) compared to the NP treatment. Regression and correlation analyses showed that soil enzyme activities were positively correlated with soil nutrients. Discussion: The interaction between NT and manure application regulated soil physical structure, thereby enhancing the activities of enzymes related to carbon and nitrogen cycling. This led to a significant increase in carbon and nitrogen storage, ultimately improving crop yield. The continuous input of manure and the improved availability of nitrogen fractions were identified as the core factors contributing to the yield gain. This study confirms that no-tillage combined with manure is an effective strategy for coordinating soil carbon sequestration and stable crop yield improvement, providing a feasible management optimization approach for the promotion of no-tillage technology.