Effects of soil and water conservation tillage on soil water and nitrogen supply in sloping rotation 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 techniques of the soil and water conservation tillage significantly increased the SWS, compared with the CK. Notably, the TP-R treatment was achieved in the highest SWS for both maize and soybean during their entire growing seasons, which was 12.40% and 13.78% higher than that under CK, respectively. There was the synergistic effect of the combined contour and ridge tillage with the furrow diking on the soil water retention. Drought stress was then alleviated in the sloping black soil. (2) These tillage practices effectively improved the N absorption and utilization efficiency of both maize and soybean. The TP-S treatment exhibited superior performance during the maize growing season in the multiple N-related indicators. The N translocation efficiency of stems and leaves increased by 34.81% and 53.79%, respectively, compared with the CK. While the N absorption efficiency was enhanced by 60.00%, and the partial factor productivity of nitrogen fertilizer (PFPN) by 26.44%. Furthermore, the N harvest index (NHI) of TP-S was 3.97%-12.21% higher than that of the rest groups. The N grain contribution rate of TP-R was 54.52% greater than that of the CK. In soybean fields, the RF-S treatment increased the N translocation rate of stems and leaves by 42.44% and 15.12%, compared with the CK. The TP-S treatment significantly improved the petiole N translocation rate (20.08%), N grain contribution rate (56.99%), N absorption efficiency (82.93%), and NHI (10.14%), compared with the CK, with its PFPN of 9.49% higher than the average value over all seven treatments. (3) All treatments of the soil and water conservation tillage promoted the crop growth and yield formation. The best performance was observed in the measured indicators under the TP-S treatment, including plant height, aboveground biomass, and final grain yield. In conclusion, the soil and water conservation tillage, particularly the combined tillage practices, can serve as a promising and sustainable approach to effectively enhance soil water content, NUE, and crop yield in the sloping black soil under maize-soybean rotation. Among them, the TP-S treatment is the most significant for agricultural application in similar sloping black soil regions. This finding can also provide a strong reference to promote the sustainable utilization of the black soil resources, in order to reduce soil degradation for regional food security.