Improving Root Nitrogen Uptake via Organic Fertilizer Substitution Enhances Yield and Efficiency in Dryland Maize

Using a maize planting system with full film mulching on double ridges and furrow sowing in the arid and semi-arid regions of the Loess Plateau, this study aims to explore the optimal proportion of organic fertilizer to replace basal chemical fertilizers; clarify its regulatory mechanism on nitrogen metabolism in maize roots and yield, so as to simultaneously achieve the reduction in chemical fertilizers and stable yield increase; and provide technical support for the global green production of dryland agriculture. Using fully mulched ridge–furrow cropping maize as the research object, four treatments were established with an equal nitrogen application rate (200 kg/hm2): 100% chemical fertilizer (T1), 50% chemical fertilizer + 50% organic fertilizer (T2), 62.5% chemical fertilizer + 37.5% organic fertilizer (T3), and no fertilization (T4). The nitrogen content in roots, metabolic enzyme activities in different soil layers during the filling stage, as well as indicators such as yield and nitrogen use efficiency were measured. The T3 treatment showed the highest root nitrogen content, accumulation, and metabolic enzyme activity in the 0–20 cm soil layer. The nitrogen assimilation amount after flowering was 10.7% higher than that of T1. The grain yield and grain weight per ear were the highest in two years, reaching 6388.9 kg/hm2 in 2022, which was 11.8% higher than that of T1. The agronomic utilization efficiency increased by 22.8%, while the partial productivity of nitrogen fertilizer increased by 11.5%. The T2 treatment led to yield loss due to the excessive application of organic fertilizer. Overall, substituting 37.5% of the basal chemical fertilizer with organic fertilizer enhanced root activity and nitrogen metabolism enzyme activities, thereby improving nitrogen uptake and translocation efficiency, which ultimately increased kernel number per ear and kernel weight per ear, leading to higher grain yield. Therefore, this approach can be recommended for the green production of maize in the arid and semi-arid regions of the Loess Plateau.