Efficient water and nitrogen management is essential for maintaining soil fertility and achieving sustainable agricultural production, especially in arid oasis regions where soil degradation and nutrient loss are common challenges. However, the interactions between irrigation regimes, nitrogen application, and soil biological processes in such environments remain insufficiently understood. This study investigated the effects of water and nitrogen management on the sustainability of sandy soil nutrients within the context of the sustainable development goals during silage maize cultivation in the oasis irrigation area of the Hexi Corridor, Northwest China. Four irrigation regimes and five nitrogen management regimes were tested. The results indicate that ammonium nitrogen (NH₄⁺-N) varied significantly during the jointing stage (W4 treatment), ranging from 3.52 to 16.38 mg/kg (p < 0.05). Nitrate nitrogen (NO₃⁻-N) exhibited significant differences during the tasseling stage (W1 treatment), with a range of 6.16–21.58 mg/kg (p < 0.05). Soil total phosphorus (STP) gradually declined from early to late growth stages, ranging from 0.20 to 0.97 g/kg. Regarding enzyme activity, alkaline phosphatase (ALP) increased progressively throughout the growth period, with a range of 0.02–0.14 mg/g/d, while urease (URE) showed a declining trend, ranging from 0.25 to 0.66 mg/g/d. Water management exerted a significant negative effect on soil enzyme activity (p < 0.05), while nitrogen fertilization had a minimal impact on soil microbial communities (p > 0.05). Growth stage and irrigation regime are key regulators of the soil–microbe–enzyme activity system. The crop’s nutrient demand cycles and microbially mediated nutrient transformations exhibited strong dependence on growth stage. Enzyme activity is notably and positively affected by nitrogen inputs and plant developmental stages, while microbial biomass is mainly regulated by soil C, N, and P contents and enzyme activities. These findings provide a scientific basis for implementing water-saving irrigation and high-efficiency fertilization strategies in oasis agricultural systems.

Nitrogen deposition has great effects on vegetation characteristics and then affects soil erosion. This study was conducted to quantify the effects of vegetation characteristics induced by nitrogen addition on runoff and sediment yield. The Bothriochloa ischaemum (Linn.) Keng. was planted and applied NH4NO3 at levels of 0, 2.5, 5, and 10 g N m-2 yr-1 for three years with the bare soil for control. Then all treatments were subjected to simulated rainfall (1.0, 1.5, and 2.0 mm min-1). Results showed that nitrogen addition increased plant coverage, height, and aboveground biomass of N2.5, N5 and N10 treatments, while the root mass density of N10 was the minimum. The grassplots significantly delayed runoff starting time, reduced runoff and sediment yield. With nitrogen addition increasing, runoff starting time delayed and runoff amount decreased, although no significant difference of runoff amount was found under the high rainfall intensity. Moreover, sediment yield would be well estimated by runoff mount, coverage and root mass density with a power function. 5 g N m-2 yr-1 seems the optimal nitrogen level in controlling soil loss due to its minimum sediment yield. The different effects of nitrogen addition on grassland community and soil erosion process identified in this study may facilitate the simulation and prediction of soil erosion in semiarid grasslands under future scenarios of global change.