Effects of Water and Nitrogen Regulation on Soil Environment and Crop Growth in a Lycium barbarum||Alfalfa System

The increasing scarcity of water and soil resources, combined with inefficient water and fertilizer management, poses significant challenges to agriculture in arid regions. This study aimed to determine an optimal water and nitrogen regulation model to alleviate water shortages and improve agricultural productivity and quality. In this study, a two-year experiment was conducted to investigate the effects of varying irrigation and nitrogen levels on the soil environment and crop growth in a <i>Lycium barbarum</i>||alfalfa system (LB||AS). The experiment involved four moisture gradients and four nitrogen application levels (using urea as the nitrogen source). The results indicated that soil moisture decreased during crop development, followed by a slow increase, with significant variation across soil depths. Soil temperature peaked during the fruiting stage of <i>Lycium barbarum</i> in July, decreasing significantly with soil depth. Higher temperatures were recorded in N0 under the same irrigation level and in W3 under the same nitrogen level. Soil organic carbon (SOC) levels increased by 16.24% in W3N0 and by 18.05% in W2N1, compared to W0N3. Easily oxidizable organic carbon (EOC) and soluble organic carbon (DOC) levels exhibited significant variations depending on irrigation and nitrogen treatments. Irrigation and nitrogen had a stronger individual impact on alfalfa height and stem thickness than their combined effects. Water and nitrogen regulation significantly influenced <i>Lycium barbarum</i> yield, its 100-fruit weight, and economic efficiency (<i>p</i> < 0.05). The W0N2 treatment produced the highest yield (3238 kg·ha^-1), exceeding other treatments by up to 29.52%. In conclusion, the optimal water-nitrogen regulation model for the LB||AS system is full irrigation (75-85% <i>θ_fc</i>) with a nitrogen application rate of 300 kg·ha^-1. These findings offer critical insights for improving water and nitrogen management strategies in arid regions.