Optimal irrigation for wheat-maize rotation depending on precipitation in the North China Plain: Evidence from a four-year experiment

The North China Plain (NCP) is a remarkable agricultural area with severe water scarcity and uneven precipitation, especially in wheat season. Optimizing irrigation strategies to increase water productivity (WP) and achieve higher yield in winter wheat-summer maize rotation is urgently needed and has been a persistent challenge. A four-year field experiment was conducted to explore the impact of irrigation on yield and WP of wheat and subsequent maize under different precipitation year types (dry and normal years, categorized based on the cumulative precipitation from sowing to jointing stage of wheat (P1)). Four irrigation strategies (W0, no irrigation; W1, pre-sowing irrigation; W2, pre-sowing + jointing irrigation; and W3, pre-sowing + jointing + anthesis irrigation) were adopted for wheat, and identical field operations were applied for maize. Results showed that wheat yield was affected by P1 rather than total precipitation. Irrigation improved wheat yield by enhancing evapotranspiration, spike number, grain number, and 1000-seed weight. The water-limited gap in yield and WP between W2 and W1 was significantly higher than those between W1 and W0, and between W3 and W2, implying that W2 was the suitable irrigation strategy in wheat production. Different irrigation in wheat season had no effect on subsequent maize in normal years, but W1 increased maize yield and WP by 13.2–29.3% and 16.1–41.8% compared with other treatments through decreasing soil water storage before maize sowing in dry years. Therefore, we recommended W2 to achieve higher annual yield, WP, and net income in normal years (37.6 mm < P1 < 79.9 mm); and W1 to lower irrigation water consumption and achieve higher WP and economic benefits in dry years (P1 < 37.6 mm), respectively. Overall, optimizing irrigation under different precipitation conditions is an effective strategy to cope with water resource shortages and increase crop yield and WP in the NCP.