中文摘要：

2002—2004年对宁南旱区不同生长年限紫花苜蓿土壤理化性状和紫花苜蓿-谷子轮作进行了研究。结果表明，随着紫花苜蓿生长年限延长，土壤生态环境得到改善。紫花苜蓿3～22年生期间，0～100cm土壤容重减少了0．213g／cm^3，孔隙度增加8．03％，饱和持水率增加14．17％，持水能力增强。6～22年生期间，0～60cm土层有机质和碱解氮平均含量分别增加1．60g／kg和11．02mg／kg，pH值降低了0．09，为轮作作物生长创造了良好的土壤环境。紫花苜蓿轮作年份越早，土壤水分恢复效果越好，轮作作物水分利用效率越高；反之，紫花苜蓿生长时间过长，轮作后不利于土壤水分的恢复。6，10和22年生紫花苜蓿地轮作谷子收获后，0～200cm土壤水分恢复量分别为63．06，55．22和-42．55mm，轮作谷子产量分别为1725．95，1485．80和1560．75kg／hm^2，水分利用效率分别为12．0116，8．4325和5．8161kg／mm·hm^2。为使旱区农地有限的土壤水分达到合理、高效及可持续利用，取得较大的经济效益、生态效益和社会效益，紫花苜蓿实行草粮轮作的最适宜年限在5～6年生。

英文摘要：

Soil physical and chemical properties were studied under different age Medicago sativa and M. sativa-millet crop rotations in the arid region of Southern Ningxia from 2002 to 2004. The soil ecological environment improved with increasing years of M. sativa growth. When M. sativa was grown from 3 to 22 years, soil bulk density was reduced by 0. 213 g/cm^3 , soil porosity increased by 8.03%, and the soil-water saturation ratio increased 14.17%, so soil water holding capacity was strengthened. From 6-22 years of M. sativa growth resulted in soil organic matter and nitrogen content in the 0-60 cm depth increasing by 1.60 g/kg and 11.02 mg/ kg respectively while pH fell by 0.09, thus supplying a better soil growing environment for rotation crops. The more years of M. sativa rotation, the better the effect on soil moisture restoration and the higher the water use efficiency （WUE） of rotation crop. When millets were harvested after 6, 10, and 22 years old M. sativa growth, soil water restoration contents in the 0-200 cm depth were 63.06 mm, 55.22 mm, and -42.55 mm respectively. Millet yields in the M. sativa-grain crop rotation were 1 725.95 kg/hm^2 , 485.80 kg/hm^2 and 1 560.75 kg/hm^2 and their WUE were 12. 011 6 kg/mm · hm^2 , 8. 432 5 kg/mm · hm^2 and 5. 816 1 kg/mm · hm^2 respectively. Therefore, to make effective and sustainable use of limited soil water in the arid region farmlands and to achieve better economy, ecology and society benefit, the optimum growth period of M. sativa in crop rotations is 5-6 years.