Slow-release nitrogen fertilizers enhance crop production and reduce environmental pollution, but their slow nitrogen release may cause insufficient nitrogen supply in the early stages of crop growth. Mixed nitrogen fertilization (MNF), combining slow-release nitrogen fertilizer with urea, is an effective way to increase yield and income and improve nitrogen fertilizer efficiency. This study used urea alone (Urea) and slow-release nitrogen fertilizer alone (C/SRF) as controls and employed meta-analysis and a random forest model to assess MNF effects on crop yield and nitrogen partial factor productivity (PFPN), and to identify key influencing factors. Results showed that compared with urea, MNF increased crop yield by 7.42% and PFPN by 8.20%, with higher improvement rates in Northwest China, regions with an average annual temperature ≤ 20 °C, and elevations of 750–1050 m; in soils with a pH of 5.5–6.5, where 150–240 kg·ha⁻¹ nitrogen with 25–35% content and an 80–100 day release period was applied, and the blending ratio was ≥0.3; and when planting rapeseed, maize, and cotton for 1–2 years. The top three influencing factors were crop type, nitrogen rate, and soil pH. Compared with C/SRF, MNF increased crop yield by 2.44% and had a non-significant increase in PFPN, with higher improvement rates in Northwest China, regions with an average annual temperature ≤ 5 °C, average annual precipitation ≤ 400 mm, and elevations of 300–900 m; in sandy soils with pH > 7.5, where 150–270 kg·ha⁻¹ nitrogen with 25–30% content and a 40–80 day release period was applied, and the blending ratio was 0.4–0.7; and when planting potatoes and rapeseed for 3 years. The top three influencing factors were nitrogen rate, crop type, and average annual precipitation. In conclusion, MNF should comprehensively consider crops, regions, soil, and management. This study provides a scientific basis for optimizing slow-release nitrogen fertilizers and promoting the large-scale application of MNF in farmland.

This study posits that strategically optimizing irrigation and fertilization regimes can enhance the productivity and water use efficiency (WUE) of alfalfa (Medicago sativa L.), thereby mitigating the constraints imposed by soil impoverishment and water scarcity in forage production systems of arid and semi-arid regions. Conducted over two years, the outdoor pot experiment investigated the effects of water regulation during the branching and bud stages (each at 60–100% θ_0.85, where θ_0.85 = 0.85θfc) and different levels of nitrogen and phosphorus fertilization (0–280 kg/ha each) on alfalfa yield and WUE. Using Response Surface Methodology (RSM) with a Central Composite Design (CCD), we modeled the relationships between input variables and key response parameters: total yield, evapotranspiration (ET), and WUE. The response surface models exhibited high reliability, with coefficients of determination R², adjusted R², predicted R², and adequate precision exceeding 0.94, 0.90, 0.86, and 13.6, respectively. Sensitivity analysis indicated that water regulation during critical growth stages, particularly the branching stage, had the most significant impact on yield and ET, while nitrogen and phosphorus fertilization positively influenced WUE. Within the appropriate range of water management, judicious fertilization significantly enhanced alfalfa production performance, although excessive inputs resulted in diminishing returns. This study identified the optimal conditions for sustainable production: branching stage water regulation (82.26–83.12% θ_0.85) and bud stage water regulation (78.11–88.47% θ_0.85), along with nitrogen application (110.59–128.88 kg/ha) and phosphorus application (203.86–210 kg/ha). These findings provide practical guidelines for improving the sustainability and efficiency of alfalfa production in resource-limited environments.

The addition of phosphorus fertilizer plays a critical role in improving alfalfa yield and quality. However, improper application may lead to resource waste and environmental pollution, and its effects are influenced by multiple factors. This study quantitatively analyzed the effects of phosphorus fertilization on alfalfa yield, crude protein (CP) content, acid detergent fiber (ADF) content, and neutral detergent fiber (NDF) content and their major influencing factors using a meta-analysis method by integrating data from published field experiments. The results showed that, compared to no phosphorus application, phosphorus fertilization increased alfalfa yield, CP content, and NDF content by 19.0% (confidence interval [CI]: 15.4–22.6%), 7.2% (CI: 0.1–14.9%), and 7.2% (CI: 0.1–14.9%), respectively, while reducing ADF content by 3.3% on average (CI: 0.9–3.3%). In Shandong, Jilin, and Hebei, where the soil pH is 7–8, annual precipitation is 200–400 mm, annual mean temperature is above 4 °C, and altitude is 500–1000 m, alfalfa yield improved after applying calcium phosphate or single superphosphate with a P₂O₅ content of 0–20% at a rate of 100–200 kg·ha⁻¹, along with nitrogen > 100 kg·ha⁻¹, and when both the test and establishment periods were 2 years. In Xinjiang, in regions with an annual mean temperature of 6–8 °C and an establishment duration of 3 years, phosphorus fertilization improved alfalfa quality. This study provides references for enhancing alfalfa productivity and efficient utilization of phosphorus nutrition.

To address low productivity and water constraints in lucerne fields of China’s Gansu Yellow River Irrigation Region, this study optimized lucerne (Medicago sativa L.) cultivation through synergistic planting nitrogen regimes. A two-year field trial (2021–2022) evaluated three systems: ridge-furrow with ordinary mulch (PM), ridge-furrow with biodegradable mulch (BM), and conventional flat planting (FP), under four controlled-release N rates (0, 80, 160, 240 kg ha⁻¹). Multidimensional assessments included growth dynamics, dry matter yield, forage quality (crude protein [CP], acid/neutral detergent fiber [ADF/NDF], relative feed value [RFV]), and resource efficiency metrics (water use efficiency [WUE], irrigation WUE [IWUE], partial factor productivity of N [PFPN], agronomic N use efficiency [ANUE]). The results showed the following: (1) Compared with conventional flat planting, ridge planting with film mulching significantly promoted lucerne growth, with ordinary plastic film providing a stronger effect than biodegradable film. Plant height and stem diameter exhibited a quadratic response to elevated nitrogen (N) application rates under identical planting patterns, peaking at intermediate N levels before declining with further increases. (2) Ridge planting with both ordinary plastic film and biodegradable film combined with an appropriate N rate improved lucerne yield and quality. In particular, the PMN2 treatment reached the highest value of yield (14,600 kg ha⁻¹), CP (19.19%) and RFV (124.18), and the lowest value of ADF (29.63%) and NDF (48.86%), and all of them were significantly better than the other treatments (p < 0.05). (3) WUE, IWUE, PFPN, and ANUE followed the pattern PM > BM > FP. With increasing N application rates, WUE, IWUE, and ANUE initially rose and then declined, peaking under N2, whereas PFPN showed a decreasing trend and reached its maximum under N1. Principal component analysis revealed that ridge planting with ordinary plastic film combined with 160 kg·ha⁻¹ N (PMN2) optimized lucerne performance, achieving balanced improvements in yield, forage quality, and water–nitrogen use efficiency. This regimen is recommended as the optimal strategy for lucerne cultivation in the Gansu Yellow River Irrigation Region and analogous ecoregions.

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 Lycium barbarum||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 Lycium barbarum 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 Lycium barbarum yield, its 100-fruit weight, and economic efficiency (p < 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% θ_fc) 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.

Agroforestry is an ecological agricultural model that promotes the coordinated development of agriculture and animal husbandry. Exploring appropriate water and nitrogen management strategies for forage grasses in agroforestry systems is of great significance for improving productivity. This study aims to investigate the effects of different water and nitrogen management practices on the growth, nitrogen uptake, and utilization efficiency of intercropped alfalfa in a goji berry-alfalfa system. It is assumed that moderate water deficiency combined with appropriate nitrogen fertilizer can optimize the growth of alfalfa in the intercropping of wolfberry and alfalfa. This study was based on a 2-year (2021 and 2022) field trial, focusing on alfalfa in a goji berry||alfalfa system. Four irrigation levels [full irrigation (W0, 75–85% θ_fc), mild water deficit (W1, 65–75% θ_fc), moderate water deficit (W2, 55–65% θ_fc), and severe water deficit (W3, 45–55% θ_fc)] and four nitrogen application levels [no nitrogen (N0, 0 kg·hm⁻²), low nitrogen (N1, 150 kg·hm⁻²), medium nitrogen (N2, 300 kg·hm⁻²), and high nitrogen (N3, 450 kg·hm⁻²)] were set up to systematically analyze the effects of water and nitrogen regulation on biomass allocation, nitrogen translocation, hay yield, and nitrogen use efficiency of alfalfa. The results showed that (1) irrigation and nitrogen application levels significantly affected the stem-to-leaf and root-to-shoot ratios of alfalfa (p < 0.01). The smallest stem-to-leaf ratio (0.758) was observed under W1N2, while the smallest root-to-shoot ratio (0.595) was observed under W0N2. (2) Irrigation and nitrogen application levels significantly affected nitrogen accumulation and nitrogen translocation in alfalfa (p < 0.05). The maximum nitrogen accumulation was observed under W0N2, which was 43.39% higher than that under W0N0. The maximum nitrogen translocation was observed under W1N2, which was 15.1% and 33.4% higher on average than that under W0N0 and W3N0, respectively. (3) Irrigation and nitrogen application had highly significant effects on alfalfa hay yield (p < 0.01). The highest hay yield (8325 kg·hm⁻² and 12,872 kg·hm⁻²) was achieved under W0N2. The nitrogen productivity of alfalfa increased with increasing water deficit and initially increased, then decreased with increasing nitrogen application. The nitrogen use efficiency of alfalfa followed the order N2 > N1 > N3 and W1 > W0 > W2 > W3, with the highest value of 9.26 under W1N2. Based on the comprehensive evaluation of alfalfa in agroforestry systems under water and nitrogen regulation using the entropy weight-TOPSIS method, mild water deficit combined with medium nitrogen application (W1N2) can optimize the stem-to-leaf ratio, root-to-shoot ratio, and nitrogen use efficiency of alfalfa without significantly reducing yield and nitrogen production efficiency. This water-nitrogen combination is suitable for use in goji berry||alfalfa systems in the Yellow River irrigation area of Gansu Province and similar ecological zones.