Matching fertilization with water availability enhances maize productivity and water use efficiency in a semi-arid area: Mechanisms and solutions

Unpredictable precipitation and frequent droughts often threaten crop productivity in semiarid areas, but this challenge can be alleviated by optimizing the nutrient supplies to match the water availability. In this study, a field experiment was conducted from 2014 to 2017 in the Loess Plateau of northwest China to determine the soil water balance and maize crop productivity in the ridge–furrow mulching system under five N + P₂O₅ fertilizer application rates: 0 + 0 (control); 117 + 59 kg ha⁻¹; 173 + 87 kg ha⁻¹; 229 + 115 kg ha⁻¹; and 285 + 143 kg ha⁻¹. Results showed that fertilization increased the evapotranspiration by 5.1–11.8 %, maize yield by 94.0–129.9 %, and water use efficiency by 89.3–116.7 %, compared with the control. However, increasing the fertilizer rate resulted in the evapotranspiration exceeding the precipitation, thereby leading to significant soil water depletion (44.9 mm – 159.6 mm), especially in the 80–200 cm soil layer., The average soil water increment during the fallow period was 49.3 mm, which was not balanced with the soil water depletion, and thus the annual soil water imbalance characterized by decreased soil water storage at sowing (SWSₛ) that became worse each year. During the course of the four-year study, SWSₛ decreased from an average of 575.5 mm in 2014 to 358.8–500.0 mm (average 398.6 mm) in 2017, and the decreases were 20.5–28.2 % greater in soils that received higher fertilizer rates compared with the control. Thus, huge fluctuations occurred in the maize yield between years, which were greater as the amount of fertilizer increased. Our results suggests that fertilizer application at a rate of N 180.9+P₂O₅ 90.5 kg ha–¹ is ideal to match with the water availability to facilitate sustainable water use and achieve high maize yields. In addition, ensuring that SWSₛ is at least 441.1 mm and the sum of SWSS plus precipitation within 90 days after sowing exceeds 624.3 mm can help to stabilize the maize grain yield in the study region.