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土壤水分受大气降水,人工灌溉,地面蒸发,作物蒸腾和其自身保蓄水分的性能而变化。云南冬春降雨很少,红壤旱地又无灌溉条件,在在雨季结束时水分含量约在20％左右。这时的土壤水分尚能保证小春作物的发芽出苗。旱季开始,随着时间的推移,土壤水分含量会迅速下降,因而抢墒播种已在生产上被广泛的应用。旱季土壤水分主要消耗于地面蒸发和作物蒸腾。作物在整个生长期所消耗的土壤水分是被认为有效性水分;而地面蒸发所消耗的土壤水分则是无效的,并且它是大量的,成为红壤早地小春生产的
Soil moisture varies with the performance of atmospheric precipitation, artificial irrigation, ground evaporation, crop transpiration and its own preserving moisture. There is very little rainfall in winter and spring in Yunnan, and there is no irrigation in the drylands of red soils. At the end of the rainy season, the moisture content is about 20%. Soil moisture at this time can still ensure the emergence of small spring sprouts germination. Dry season begins, with the passage of time, the soil moisture content will rapidly decline, so grab moisture planting has been widely used in production. Soil moisture in dry season is mainly consumed by ground evaporation and crop transpiration. Soil moisture consumed by crops throughout the growing season is considered as effective moisture, whereas soil moisture consumed by ground evaporation is ineffective, and it is abundant, becoming red as early spring