Comparison of irrigation strategies for summer maize under deficit irrigation: Grain yield and water use efficiency

The shortage of water resources in the North China Plain (NCP) poses a challenge to traditional agricultural irrigation methods. Adjusting and optimizing the irrigation mode is an important strategy for saving water and improving water use efficiency (WUE) and crop yield under water-limited irrigation conditions. Given this background, different irrigation modes were set in an automatic rainproof shed (to eliminate the effects of natural rainfall) in the two growing seasons of 2018 and 2019 to analyze the grain yield and WUE of summer maize. In this experiment, a randomized block design was adopted, and two irrigation methods were applied: border irrigation (BI) and micro-sprinkler irrigation (SI). Based on the total irrigation amount and frequency, sample plots were divided into two groups for comparison. Plots in the first group (SI-225 and BI-225) had the same total irrigation amount (50% of evapotranspiration, ET) but different irrigation frequencies. SI-225 was irrigated six times, namely at the emergent seedling stage (VE), sixth leaf stage (V6), tenth leaf stage (V10), thirteenth leaf stage (V13), tasseling stage (VT), and milk stage (R3). BI-225 was irrigated three times at VE, V10, and VT. Plots in the second group (SI-225, SI-280, SI-352, and BI-450) had the same irrigation frequency but different total irrigation amounts (50%, 60%, 80%, and 100% of ET). Among them, SI-225 and BI-450 received a fixed amount of water per irrigation event, whereas SI-280 and SI-352 underwent supplementary irrigation according to their soil moisture content. The results showed that, compared with those of BI-225, the grain yield of SI-225 increased by 17.7%−20.2% and its WUE increased by 9.2%−12.7%. Further analysis of physiological characteristics revealed that SI-225 showed an improved upper soil water status (0−40 cm), increased photosynthetic rate (P_n), leaf area index (LAI), and dry matter accumulation, and consequently higher yield and WUE due to modest but highly frequent irrigation. Under the same irrigation frequency, the grain yields of SI-225 and SI-280 decreased by 21.2% and 12.0%, respectively, compared with that of BI-450. However, total water consumption during the growth period was reduced due to the decrease in LAI and transpiration rate (T_r) of SI-225 and SI-280, which resulted in an improved WUE. The grain yield of SI-352 did not differ significantly from that of BI-450, but its ET decreased by 9.8% due to the optimization of LAI and T_r, its irrigation amount decreased by 21.8%, and its WUE increased by 5.1%. Therefore, under water-limited irrigation conditions (50% of ET), the yield and WUE of summer maize could be increased by increasing the irrigation frequency, with modest but highly frequent irrigation promoting the best results. Moreover, under moderate water limitation (80% of ET), the application of micro-spraying supplementary irrigation based on soil moisture content allowed to achieve a stable yield and a high WUE. These results provide a theoretical reference for improving the efficiency of agricultural water use in water-deficient areas of the NCP.