Effects of soil and water conservation tillage on soil water and nitrogen supply in sloping rotation black soil farmland

Soil erosion and nutrient loss have been confined to sustainable agriculture in recent years. This study aims to systematically investigate the effects of soil and water conservation tillage on soil water storage (SWS) and nitrogen use efficiency (NUE) in the sloping black soil farmland. A typical maize-soybean rotation was also selected as the research subject. A two-year field experiment was conducted in a black soil region. Seven tillage treatments were designed to compare single and combined conservation: 1) Single tillage group: contour tillage (TP), ridge tillage with furrow diking (RF), and subsoiling tillage (SF); 2) Combined tillage group: contour tillage integrated with subsoiling (TP-S), ridge tillage with furrow diking combined with subsoiling (RF-S), and contour tillage coupled with ridge tillage with furrow diking (TP-R); 3) Control group: conventional tillage (CK), according to the local conventional farming procedures without any additional soil and water conservation. A systematic investigation was made into the impacts of these tillage techniques on the indicators. Specifically, the agro-ecological and production indicators were determined, including farmland SWS at 0–100 cm soil depth, nitrogen (N) absorption capacity, N translocation and utilization efficiency, crop growth-related traits (e.g., plant height, dry matter accumulation, and leaf area index), and final grain yield under the maize-soybean rotation. The results demonstrated that: 1) All soil and water conservation tillage practices effectively improved soil water storage (SWS). The TP-S treatment exhibited the greatest SWS capacity for both maize and soybean across the growing seasons, with SWS values increased by 11.94% and 14.48%, respectively, compared with the conventional control (CK). 2) Soil and water conservation tillage substantially enhanced nitrogen uptake and utilization in maize and soybean. During the maize growing season, the TP-S treatment markedly increased the nitrogen translocation efficiency of stems and leaves, nitrogen uptake efficiency, and partial factor productivity of nitrogen fertilizer (PFPN) by 53.40%, 116.40%, 60.00%, and 26.44%, respectively, relative to CK. Meanwhile, the nitrogen harvest index (NHI) and grain nitrogen contribution rate of the TP-S treatment were elevated by 12.21% and 97.72% compared with CK. For soybean, the TP-S treatment increased the nitrogen translocation rates of stems, leaves, and petioles by 37.86%, 114.19%, and 20.08% over CK. Furthermore, the TP-S treatment achieved significant improvements in key nitrogen utilization indicators, with a 90.00% increase in grain nitrogen contribution rate, a 27.29% increase in PFPN, an 82.93% increase in nitrogen uptake efficiency, and an 11.28% increase in NHI compared with the CK treatment. 3) Relative to conventional tillage, all soil and water conservation tillage practices positively promoted crop growth and yield formation, with the TP-S treatment obtaining the optimal performance in all measured agronomic indicators. In summary, soil and water conservation tillage serves as a promising and efficient field management strategy to improve soil water status, enhance nitrogen use efficiency, and increase crop yield. Specifically, the integrated practice of contour tillage combined with subsoiling (TP-S) yields the most prominent regulating effects, which possesses great potential for field popularization and application in similar agricultural regions.