Objective To address the core issues of poor water and nutrient retention capacity, weak structural stability, and low crop productivity in sandy soils in the arid areas of Northwest China, the synergistic effects of partial nitrogen substitution with organic fertilizer and irrigation reduction on soil physicochemical properties, aggregate characteristics, nutrient uptake, and grain yield of maize in different soil layers were systematically investigated, providing theoretical support for sandy soil improvement and water-saving and high-yield maize cultivation in this region.

Methods This study was conducted at the Ningxia Central Station of the China Irrigation Experiment, Ministry of Water Resources, from 2024 to 2025. A split-plot design was employed, with two fertilization treatments in the main plot: chemical fertilizer (F1) and organic fertilizer instead of 30% nitrogen fertilizer (F2). The subplot comprised four irrigation levels: conventional irrigation (W1), deficit irrigation by 12.5% (W2), deficit irrigation by 25% (W3), and deficit irrigation by 37.5% (W4). Soil physicochemical properties, aggregate composition and stability in the 0−20 cm, 20−40 cm, and 40−60 cm layers, along with maize N, P, and K accumulation, distribution, and grain yield were determined.

Results 1) Compared with pure chemical fertilizer (F1), the coupling treatment of organic fertilizer instead of 30% nitrogen fertilizer (F2) combined with 12.5% (W2) irrigation reduction could significantly increase soil saturated water content and field water holding capacity in 0—20 cm, 20—40 cm and 40—60 cm soil layers, and the improvement effect on deep soil was more prominent. Among them, the soil saturated water content and field capacity in the 40—60 cm soil layer increased by 12.10% and 28.23% on average, respectively. In terms of soil available nutrients, the coupling treatment had a more significant improvement effect on the surface soil. The contents of available nitrogen, available phosphorus and available potassium in the 0—20 cm soil layer increased by 10.10%-63.96%, 9.73%-74.50% and 6.32%-53.69%, respectively. 2) The F2W2 treatment significantly increased macro-aggregate content across all soil layers, with the most pronounced improvement in the 0−20 cm layer. The treatment significantly increased the proportion of >5 mm mechanically stable and water-stable aggregates while reducing <0.25 mm microaggregate proportion. For mechanically stable aggregates, the mean weight diameter (MWD), geometric mean diameter (GMD), and R₀.₂₅ increased by 7.45%−22.55%, 13.22%−38.92%, and 5.04%−14.22%, respectively. For water-stable aggregates, MWD, GMD, and R₀.₂₅ increased by 12.05%−41.78%, 13.78%−40.20%, and 5.28%−15.78%, respectively. The increases in water-stable aggregate indices were consistently greater than those in mechanically stable aggregates. 3) The F2W2 treatment significantly increased maize N, P, and K accumulation and effectively promoted nutrient translocation to grains. Grain yield under W2 was 4.46%−14.53% higher than under other treatment combinations. PLS-SEM analysis revealed that fertilization treatments and irrigation levels positively regulated soil moisture and nutrient status, thereby improving aggregate composition and stability, which in turn promoted maize nutrient accumulation and ultimately synergistically enhanced grain yield.

Conclusions Substituting 30% of chemical N fertilizer with organic fertilizer coupled with 12.5% deficit irrigation (F2W2) effectively improves sandy soil structure and enhances soil water and nutrient retention capacity, which is the optimal water−nutrient synergistic management strategy for achieving grain yield gains in sandy soils of Northwest China's arid regions.