Effects of soil preparation and mulching practices together with different urea applications on the water and nitrogen use of winter wheat in semi-humid and drought-prone areas

Soil preparation and mulching practices in combination with slow-release urea application are important measures for agricultural yield enhancement. However, slow-release urea may cause a yield reduction due to insufficient fertility in early crop growth. We considered whether the ridge-furrow plastic-mulching (RFP) system using different mulch colors could offset this disadvantage. An experiment was conducted using a randomized split-plot design with three soil preparation and mulching practices as the main-plot treatments in combination with three different urea applications as sub-plot treatments. The three soil preparation and mulching practices were flat cropping without mulch (F), the RFP system with white plastic mulch over the ridge (W), and the RFP system with black plastic mulch over the ridge (B); the three urea applications were no urea (N0), slow-release urea (NS), and ordinary urea (NU). The results showed that compared to F, the RFP system (especially B) could increase the use of precipitation and reduce soil water depletion, which ultimately increased the water productivity (WP) of winter wheat. In addition, the nitrogen use efficiency of NS was further improved under the RFP system, while there was essentially no difference between the two different urea types under F. In summary, B could take full advantage of NS to coordinate the relationship between effective spikes per unit area, grains per spike, and 1000-grain weight, maximizing the WP, nitrogen use efficiency, and grain yield. Between 2016 and 2019, the WP and grain yield of B-NS increased by 79.2–107.0% and 75.7–87.0%, respectively, compared to the lowest value (F-N0). The nitrogen agronomic efficiency (NAE), nitrogen physiological efficiency (NPE), nitrogen recovery efficiency (NRE), and nitrogen partial factor productivity (NPFP) of B-NS increased by 116.1–123.3%, 28.5–34.8%, 66.1–71.9%, and 44.1–53.2%, respectively, compared with the lowest value (F-NU).