黄土高原丘陵沟壑区从事旱农生产存在的有利因素是土层深厚,土质疏松,具有良好的蓄水性能。2米深的土层,一般可蓄纳550—600毫米的水分,形成供作物生长的天然土壤水库。不利因素是因受大气环流和地理位置的影响,干旱少雨,降雨分布不均,降雨强度变率很大;同时土壤蒸发量大,降雨的高峰期也是蒸发高峰期。且坡耕地所占比重很大,如定西县旱坡地占90.8％。当降雨强度大于土壤入渗速率时,产生地面径流, Loess Plateau hilly and gully areas engaged in the production of dry farming there is a favorable factor is the soil deep, loose soil, has good water storage performance. 2 meters deep soil, generally can save 550-600 mm of water, the formation of natural soil for crop growth reservoir. Adverse factors are due to the influence of the atmospheric circulation and geographical location, aridity, uneven distribution of rainfall, large rainfall rate variability; at the same time, soil evaporation, rainfall peak is also the peak evaporation period. And the slope of a large proportion of cultivated land, such as Dingxi dry slope accounted for 90.8%. When the rainfall intensity is greater than the soil infiltration rate, resulting in runoff,