中文摘要：

刈割时间是影响紫花苜蓿产量和营养品质的关键因素之一。本研究于2009年和2010年,开展了不同的第1次刈割时间和第2次刈割时间的田间试验,分析刈割时间对紫花苜蓿产草量和营养品质的影响。结果表明,苜蓿产草量与粗蛋白产量均以初花期最高,此后随第1次刈割时间的推迟逐渐下降（P〈0.001）,第1次刈割提前会导致产草量和粗蛋白产量下降（P=0.003）。随着第1次刈割与第2次刈割间隔时间的延长,紫花苜蓿的中性洗涤纤维、酸性洗涤纤维和粗纤维含量逐渐增加（P〈0.001）,粗蛋白含量逐渐下降（P〈0.001）;初花期第1次刈割,第2次刈割间隔时间分别为72d（2009年）和68d（2010年）时,产草量和粗蛋白产量最高,分别为2275.2和180.2kg/hm2、2063.6和263.1kg/hm2。研究区紫花苜蓿适宜刈割时间为初花期（6月中旬）第1次刈割、70d左右（8月下旬）第2次刈割。

英文摘要：

Cutting time is one of the key factors affecting the yield and quality of alfalfa. In these experiments, we evaluated the effects of different cutting times in 2009 and 2010 on the yield and quality of alfalfa hay. The hay yield and crude protein yield of alfalfa were highest at the early flowering stage （P〈0 . 001）. Cutting before the early flowering stage resulted in significantly decreased hay yield and crude protein yield （P - 0. 003）. As the interval between the first and second cutting times increased, the contents of neutral detergent fiber, acid detergent fiber, and crude fiber increased （P〈0 . 001） , and the crude protein content decreased （ P 〈 0 . 00 1）. With the first cutting at early flowering, an interval of 72 days （2009） and 68 days （2010） resulted in the high-est yield and crude protein production （2275. 2 kg/ha and 180. 2 kg/ha, respectively, in 2009 ; 2063. 6 kg/ha and 263. 1 kg/ha, respectively, in 2010）. These results indicate that the appropriate time for the first cutting of alfalfa on the Loess Plateau is at the early flowering stage in mid-June, and that of the second cutting is approx-imately 70 days later in late August