Optimized sprinkler fertigation for summer maize in the North China Plain

Nitrogen fertilizer and rainfall can dominate the yield and nitrogen use efficiency for summer maize in the North China Plain. This study aims to explore the optimal schedule under sprinkler fertigation. Summer maize (Zea mays L) was selected as the experimental crop in a local cultivar (Zheng Dan No. 958). These experiments were carried out in Dacaozhuang of Hebei Province, China (37°28'N and 114°54'E) in the 2020 and 2021 seasons. The soil water content, soil nitrogen distribution, crop growth parameters, yield, water use efficiency, and nitrogen use efficiency were compared among sprinkler fertigation treatments with three nitrogen recommendations (local empirical value, mineral nitrogen, and improved mineral nitrogen) and (no, one and two) topdressing. Intermittent rainfall events were tested during the period from flare opening to the filling stage. A great rainfall event was defined as the cumulative rainfall exceeding 20 mm within a single day or several consecutive days. The topdressing date was applied 5 days after the great rainfall events, according to the rainfall forecast. As such, the normal rotation of the center pivot system was realized for all treatments. The proportion of basal N fertilizer was 40% in all top dressing treatments. The nitrogen type was urea (CO(NH₂)₂, N=46%) in the growth period. All phosphorous (monoammonium phosphate, P₂O₅=46%) and potassium (potassium chloride, K₂O=60%) were applied into the top 20 cm of soil as basal fertilizers before sowing. Surface irrigation with fertilizer broadcasting was used as the control treatment (CK) with improved mineral nitrogen and two topdressings following intermittent rainfall events during the period from flare opening to the filling stage. There were five treatments in each experimental year. All the treatments had 3 replicates and the same irrigation schedules. The plot area of each replicate was 0.39 hm² and controlled by a 20° rotation angle of the center pivot system. The CK treatment was arranged near the field with a total area of 0.48 hm². The results showed that the moisture content of the 0-100 cm soil layer remained at a high level during the growing period of summer maize, indicating no need to irrigate. The increasing rate and times of nitrogen application improved the soil inorganic nitrogen content in the root zone of summer maize. The sprinkler irrigation treatment was greater than that of the control treatment. The lower residual nitrogen was observed in soil under the treatment of nitrogen amount in the nutrient balance and the total nitrogen basal after two years of summer corn harvest, compared with the reference surplus level (50 kg/hm²). There was no significant difference in the leaf area index among different treatments. But the dry matter mass and nitrogen uptake of maize plants significantly increased by spraying irrigation treatment. The yield and nitrogen partial productivity significantly increased by 20%, compared with the control, respectively. The improved mineral nitrogen and two topdressings obtained the best performance among all sprinkler fertigation treatments. The results demonstrated that the growth index, yield, water, and nitrogen use efficiency of summer maize were closely related to the N recommendation and topdressing. The sprinkler fertilization of summer maize was recommended as the improved nutrient balance considering nitrogen surplus and the twice fertilizer application after heavy rainfall during the flared opening to filling period. The balance of the nitrogen pool was also maintained in the soil. The finding can provide a strong reference to improve the yield and nitrogen use efficiency in the North China Plain