Alfalfa (Medicago sativa L.) is one of the most important forage crops in the world. The objectives of this study were to assess alfalfa yield improvement in the Canadian prairies, and determine critical climatic factors influencing alfalfa yield in different soil zones. Forage yield data of alfalfa cultivars tested from 1997 to 2011 in the Western Forage Variety Testing System were used for the analysis. There was no significant trend of alfalfa yield increase in western Canada except at Saskatoon, SK. Regrowth yield of alfalfa cultivars released from 2000 to 2011, however, showed a significant (p ≤ 0.05) increase under irrigation. Based on structural equation modelling (SEM), at rain-fed sites, precipitation from April to June was the most important driver for the farm hay yield (1st-cut). Forage yield of alfalfa, however, was not associated with winter extreme temperatures, or number of days with freeze-thaw temperatures in April. Alfalfa yields were greatest under a 3-cut than 1- or 2-cut systems in the first production year, but this difference declined as stands became older. Alfalfa stands that were harvested more frequently were less responsive to growing season rain, but responded more strongly to increased snow cover, which may indicate reduced growth and less winder hardiness. At the irrigated sites, 1st-cut forage yield increased with accumulated temperatures above 5°C from April to June. Development of alfalfa cultivars with tolerance to early season drought and improved regrowth, without reducing winter hardiness, would be necessary to stabilize alfalfa production under changing climate in the Canadian prairies.

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加拿大草原苜蓿品种的牧草产量趋势及其与环境因素和收获管理的关系

苜蓿（Medicago sativa L.）是世界上最重要的饲料作物之一。本研究的目的是评估加拿大草原苜蓿产量的提高，并确定影响不同土壤区苜蓿产量的关键气候因素。1997 年至 2011 年在西方牧草品种测试系统中测试的苜蓿品种的牧草产量数据用于分析。除了在 SK 的萨斯卡通之外，加拿大西部的苜蓿产量没有显着增加的趋势。然而，从 2000 年到 2011 年释放的苜蓿品种的再生产量 在灌溉条件下显着增加（p ≤ 0.05）。基于结构方程模型（SEM），在雨养地点，4 月至 6 月的降水是农场干草产量（第 1 次切割）的最重要驱动因素。然而，苜蓿的牧草产量与冬季极端温度或四月冻融温度的天数无关。苜蓿在第一个生产年度的 3 次切割比 1 次或 2 次切割系统的产量最高，但这种差异随着林分的老化而下降。收割次数较多的苜蓿林分对生长季降雨的反应较弱，但对积雪增加的反应较强烈，这可能表明生长减少和抗风能力降低。在灌溉点，4 月至 6 月积温超过 5°C，第一割草料产量增加。开发耐早季干旱和改善再生的苜蓿品种，