Synergistic effects of irrigation and nitrogen application rates on grain protein yield and quality of winter wheat in the Southern Huanghuai region of China

Objectives We studied the effects of water and nitrogen (N) application rates on the distribution and transport of dry matter and N, as well as on grain protein yield and composition. The aim was to propose an potimal water-nitrogen combination to achive high yield, nutritional value, and processing quality of winter wheat in south Huanghuai region of China.

Methods Winter wheat field experiments were carried out in Yuanyang County, Henan Province, over two consecutive growing seasons from 2020 to 2022 under a winter wheat - summer maize rotation system. the rainfall in 2021 and 2022 was categorized as wet and normal, respectively. A split-plot experimental design was employed. the main factor was irrigation, no irrigation (W0) and irrigating 75 mm water at the jointing and flowering stage, respectively (W1); the subfactor was N application rate: 0 kg/hm² (N0), 180 kg/hm² (N180) and 300 kg/hm² (N300). Dry matter and N content in flag leaves, under-spike internodes and grains were measured at pre- and post-anthesis stage to calculate dry matter and N translocation and distribution. Grain yield, total protein content and key protein components were analyzed for assessment of grain nutrition and procession quality.

Results Irrigation, N application, and their interaction, increased the dry matter and N accumulation and translocation in flag leaves and under-spike internode, as well as N accumulation in grains. During two growing seasons, W1N300 exhibited significantly higher aboveground dry mater accumulation at maturing stage than the other treatments, while W1N180 was recorded highest dry matter translocation, which was 5.24% (2021−2022) higher than W1N300. Irrigation and N application enhanced the pre-anthesis translocation amount of N, with the translocation rate of pre-anthesis N at an order of N180>N300, and W1>W0. Under N application treatments, irrigation was beneficial to increasing N contribution rate to grains, and the average N translocation rate of W1N180 was higher than W1N300. N application increased grain total protein content, irrigation did not. In 2021 (wet year), W0N180 and W0N300 had comparable protein yield and protein composition, while globulin, protein contents and protein yield under WIN300 were significantly higher than W1N180, albumin content was significant lower than W1N180. In 2022 (normal year), the albumin, gliadin and protein contents of W0N180 were significantly lower than W0N300, however, W1N180 and W1N300 had compared protein yield and protein composition except for glutenin. The correlation analysis revealed that N translocation amount and contribution rate were positively correlated with grain yield (R² was 0.824, 0.581, respectively), N and dry matter translocation rates were positively correlated with N-use efficiency (R² was 0.820, 0.875, respectively).

Conclusions Moderate nitrogen fertilizer application (N 180 kg/hm²) exerted a significantly positive effect on the dry matter and N translocation characteristics of wheat plants. Irrigation enhanced the amount, translocation rate, and contribution rate of both dry matter and N translocation. However, increasing the N application rate beyond this level did not further improve wheat yield or resource use efficiency. N fertilization significantly increased the protein yield in wheat grains. Under adequate water supply conditions, a high N rate (higher than N180 kg/hm²) optimized the protein composition in wheat grains more effectively than a moderate nitrogen rate, thereby exerting a greater positive impact on the nutritional and processing quality of wheat. Taking all indicators into comprehensive consideration, the combination of irrigation with N application rate of 180 kg/hm² emerged as the optimal practice in the southern Huang-Huai region for promoting dry matter and nitrogen translocation in wheat, thus achieving a synergy among yield, quality, and efficiency. Meanwhile, applying N at a rate of 300 kg/hm² could more effectively enhance the nutritional and processing quality of wheat.