干旱区农田牧草水分平衡规律及更新周期的研究

降水量仅３００ｍｍ左右的旱农区发展农田草业，草种的更新周期受土壤水分平衡规律的影响，多年生豆科牧草苜蓿和沙打旺种植物时间不得超过３年，第３年产草量明显下降；地下根量呈递增趋势，水分平衡规律失调，部分植株因干旱而死亡，牧草的更新周期以３年为好。

THE STUDY OF BALANCING LAW AND RENEWING CYCLE OF FORAGE WATER IN AKRID REGION FARMLAND

The runoff is only about 300mm in arid region,if the farmland grass is developed,the renewing cycledgrass seeds iS affected by soil water.The growing tim e of perennial leguminous grass Medicago sativa,Astragalus adsurgens is not over 3 years,and in the third year the yield of grass obviously decreases,the rootsnumber in underground tends to increase,he balancing law of water is disorder,part plants die because ofdrought. The renewing cycle of grasses is 3 years the best.