Abstract: To investigate the effects of different fertilization treatments on the production performance and quality of alfalfa （Medicago sativa L.）， a two-year field experiment was conducted in the irrigated decertified area of the Hexi Corridor， Gansu Province， with two nitrogen （N） application levels （0 and 103.5 kg·hm^-2） and four phosphorus （P₂O₅） gradients （0， 45， 90， and 135 kg·hm^-2）. The results demonstrated that combined nitrogen-phosphorus fertilization significantly enhanced alfalfa yield and quality. The optimal treatment （N₁P₂： N 103.5 kg·hm^-2， P₂O₅ 90 kg·hm^-2） achieved a hay yield of equivalent to 16.64 t·hm^-2， representing a 26.41% increase compared to the control. Additionally， in comparison with the control， this treatment elevated crude protein （CP） content by 14.3% to 19.8% and improved the relative feed value （RFV） by 11.2%， while maintaining acid detergent fiber （ADF） and neutral detergent fiber （NDF） at 32.5% and 41.7%， respectively， approaching international standards for premium alfalfa. Structural equation modeling （SEM） revealed that nitrogen directly promoted CP accumulation by increasing internode number （path coefficient=0.24）， whereas phosphorus indirectly reduced fiber content by enhancing leaf area expansion （path coefficient=-0.17）. Economic analysis indicated that the N₁P₂ treatment yielded the highest net profit （39，791 yuan·hm^-2）， exceeding the high-phosphorus treatment （N₁P₃） by 2.7%， with phosphorus use efficiency reaching 42.6%. Based on these findings， we recommend fertilization rates of N 103.5 kg·hm^-2 and P₂O₅ 90 kg·hm^-2 for second-and third-year alfalfa cultivation in the Hexi Corridor. Furthermore， split nitrogen application combined with soil nutrient diagnostics is proposed to optimize nutrient utilization efficiency， which provides a scientific guidance for sustainable forage-livestock systems in arid regions.

Key words: Medicago sativa, Fertilization, Yield, Quality

摘要： 为研究不同的施肥处理对紫花苜蓿（Medicago sativa）生产性能和品质的影响，本试验设置施氮肥和不施氮肥2个水平，磷肥设置4个水平梯度，在甘肃河西走廊荒漠化灌区，连续2年开展紫花苜蓿施肥试验。结果表明：氮磷配施显著提升苜蓿产量与品质，其中N₁P₂处理（N 103.5 kg·hm^-2，P₂O₅ 90 kg·hm^-2）效果最佳，干草产量达16.64 t·hm^-2，较对照增产26.41%；粗蛋白（Crude protein，CP）含量提高至19.8%，相对饲喂价值（Relative feed value，RFV）提升11.2%，同时将酸性洗涤纤维（Acid detergent fiber，ADF）和中性洗涤纤维（Neutral detergent fiber，NDF）分别控制在32.5%和41.7%，接近国际优质苜蓿标准。结构方程模型（SEM）揭示氮素通过增加节间数直接促进粗蛋白积累（路径系数=0.24），磷素则通过扩大叶面积间接降低纤维含量（路径系数=-0.17）。经济效益分析表明，N₁P₂处理的净收益（39 791 元·hm^-2）较传统高磷处理（N₁P₃）提高2.7%，且磷肥利用率达42.6%。本研究提出河西走廊地区紫花苜蓿第二、三年生长期推荐施肥量为N 103.5 kg·hm^-2，P₂O₅ 90 kg·hm^-2，并建议结合分次施氮与土壤诊断实现养分高效利用，为干旱区草牧业可持续发展提供科学依据。

关键词: 紫花苜蓿, 施肥, 产量, 品质