Film Mulching Mitigates Yield Loss by Enhancing Growth and Nitrogen Uptake in Late-Sown Winter Wheat on the Guanzhong Plain

Delayed sowing has become a key constraint on winter wheat production in the Guanzhong Plain, Shaanxi Province, China, due to the widespread adoption of late-maturing maize and the delayed harvest of preceding crops. A two-year field experiment was conducted on the Guanzhong Plain to elucidate the physiological mechanisms behind yield reduction under delayed sowing and to explore potential mitigation strategies. The study examined the effects of sowing time (normal, 10-day delay, and 20-day delay) and plastic film mulching on yield components, crop development, and water and nitrogen uptake and use in winter wheat. Compared to normal sowing, delayed sowing significantly reduced grain yield (7.64–17.19%), spike number (11.65–21.3%), 1000-grain weight (5.2–9.05%), growth duration (7–16 d), dry matter accumulation (21.79–58.07%), and partial factor productivity of nitrogen fertilizer (7.64–17.2%). Late sowing slowed overall growth and development, shortened the growth cycle, and suppressed root system expansion and plant height, particularly under the 20-day delay. However, plastic film mulching under delayed sowing improved seedling emergence, root growth, tiller number (8.42–51.23%), water use efficiency (10.15–18.15%), and nitrogen productivity, thereby mitigating the adverse effects of delayed sowing on resource capture. Mulching enabled wheat sown with a 10-day delay to achieve yields comparable to normal-sown crops and alleviated 9.1–10.3% of the yield loss under a 20-day delay, although it did not fully restore yields to the non-delayed level. These findings provide practical insights for managing winter wheat under delayed sowing conditions.