Grain yield and resource efficiency responses to water-nitrogen coupled input reduction: A global meta-analytical perspective

Global water scarcity and excessive use of fertilizers have become important challenges for sustainable agricultural development. The effects of water-nitrogen coupling management under water-reduced and fertilizer-reduced conditions on the yield, water use efficiency (WUE), and nitrogen partial factor productivity (NPFP) of field crops, such as maize, wheat, and potatoes, were evaluated in this study via a meta-analysis. The findings demonstrated that while maintaining high yields, modest water and nitrogen reductions (about 10 %) substantially increased crop WUE and nitrogen use efficiency. On the other hand, extreme decreases in nitrogen and water led to a significant drop in production, especially for potatoes, which suffered the largest yield loss. Additionally, the effects of water-nitrogen coupling were strongly influenced by soil types, climate, and organic matter content. Compared to semi-humid environments, crops grown in arid and semi-arid environments were more sensitive to decreases in fertilizer and water. Water-nitrogen coupling management could optimize resource allocation, reduce water and fertilizer inputs, and improve crop productivity and resource utilization efficiency. The ideal levels of fertilization and irrigation for maize, wheat, and potatoes under water-nitrogen coupling conditions were 0.87I (I: full irrigation volume) and 0.81 N (N: maximum nitrogen application), 0.92I and 0.91 N, and 0.98I and 0.85 N, respectively. The maximum yields for maize, wheat, and potatoes at these levels were 1.3 × 104 kg·ha−1, 8.9 × 103 kg·ha−1, and 9.2 × 104 kg·ha−1, respectively. The yields achieved through integrated water-nitrogen management were significantly higher than those obtained from separate irrigation or fertilization treatments. Furthermore, when compared to isolated water or nitrogen management practices, the coupling of water and nitrogen not only enhanced yield but also reduced the overall input of both water and fertilizer. These findings provided robust scientific evidence to support the optimization of water-nitrogen coupling strategies. This approach held considerable practical significance, especially in the context of escalating water scarcity and growing environmental concerns related to agricultural practices.