黄土丘陵区沙打旺草地土壤水分过耗与恢复

Over depletion and recovery of soil moisture on Astragalus adsurgens grasslands in the loess hilly-gully region

研究了黄土丘陵区沙打旺 (Astragalusadsurgens)草地土壤水分的动态规律和恢复过程及人为调控土壤水分的效果。结果表明 :沙打旺在该区生长年限为 6～ 7a,生物量形成的高峰期在第 3～ 4年 ,之后土壤水分大量亏缺 ,生物量逐年下降 ,第 6年生物量和水分均下降到最低点。同时土壤水分的消耗深度与根系的分布相一致 ,土壤干层主要集中在根系分布的密集区 0 .3～0 .8m。随着沙打旺生长年限的延长及根系的下扎 ,土壤干层逐渐加深 ,3～ 6年生沙打旺草地土壤干层平均厚度为 2 .3m;土壤水分要自然恢复到种植前的含水量需要 6～ 7a;通过水平阶和水平沟整地进行人工调控 ,土壤水分比自然恢复可提前 2～ 3a,一般需要 4～ 5

Dynamic laws and recovery process of soil moisture on A. adsurgens grasslands, as well the regulation effects of soil moisture by taking engineering measure in loess hilly-gully region are researched. The results show that A. adsurgen grows only six to seven years in the loess hilly-gully region. The maximum biomass in the growth process of A. adsurgen occurs in the third and fourth years. Thereafter, A. adsurgen growth slows down and its biomass decreases due to deficiency of soil moisture on A. adsurgens grasslands. The minimum biomass occurs in the six years of A. adsurgen growth and soil water content reaches the lowest value in that year. Meanwhile, the depth of soil moisture consumption is consistent with the distribution of root system. The soil dry-layer, where soil water content is less than withering coefficient, mainly distribute at dense root system zone, i.e., 0.3～0.8 m of soil profile. As the growth year of A. adsurgen increases and root system grows into deep soil layer, the soil dry-layer gradually deepens. The average thickness of soil dry-layer in A. adsurgens grasslands, where A. adsurgens age is three to six-years, is 2.3 m. Soil moisture recovers to the condition before A. adsurgens plantation needs six to seven years under natural restoration. However, after taking engineering measure, such as constructing level ditch, the soil moisture recovery needs four to five years, which is earlier two to three years than that under natural restoration.