黄土高原半干旱区苜蓿草地土壤干燥化特征与粮草轮作土壤水分恢复效应

Soil desiccation characteristics of alfalfa grasslands and soil water restoration effects in alfalfa-grain crop rotations on the semi-arid areas of the Loess Plateau

实地测定了黄土高原半干旱区固原不同生长年限苜蓿草地和连作8a苜蓿草地翻耕轮作不同年限粮食作物后深层土壤水分特征,分析了苜蓿草地土壤干燥化特征和粮草轮作对土壤水分的恢复效应。结果表明：（1）苜蓿连作1a、5a、8a和12a等4类苜蓿草地0~1000cm土层平均土壤湿度值为6.6%,平均土壤水分过耗量702.8mm,平均土壤干燥化速率147.1 mm/a,达到强烈干燥化程度,苜蓿连作5a土壤干层深度超过1000cm,苜蓿连作8a土壤干层深度超过1360cm,苜蓿草地合理利用年限为7a。（2）连作8a苜蓿草地翻耕并轮作4~7a和25a粮食作物等5类粮田0~1000cm土层土壤湿度介于6.74%~11.95%,土壤贮水量恢复值介于210.6~887.3mm,平均土壤水分恢复速率为80.8mm/a。轮作6a后粮田土壤干层轻度恢复程度以上深度达到1000cm。通过粮草轮作使苜蓿草地土壤湿度恢复到当地土壤稳定湿度需要13a以上。黄土高原半干旱区适宜的粮草轮作模式为：7a苜蓿→13a粮食作物。

Soil water consumption characteristics of deep soil profile on different growth age alfalfa grasslands and soil water restoration effects in alfalfa-grain crop rotation fields were investigated and analyzed at Guyuan of semi-arid areas of the Loess Plateau.The results showed as followings：（1） Average soil moisture in 0-1000cm soil profile on 4 kinds of 1-12 year-old alfalfa grasslands was 6.6%,and soil water overuse amount was 702.8mm,and soil desiccating rate was 147.1mm per year,the soil desiccation intensity was strong desiccated.Thickness of desiccated soil layers was over 1000cm on the 5 year-old alfalfa grassland,and it was over 1360cm on 8 year-old alfalfa grassland.Suitable age for alfalfa grassland use was 7 year-old.（2） Soil moisture in 0-1000cm soil profile on 5 kinds of 4-7 years and 25 years alfalfa-grain crop rotation fields ranged from 6.74% to 11.95%,and soil water restoration amount was 210.6-887.3mm,and average soil water restoring rate was 80.8mm per year.Depth of restored soil layers over slight restoration intensity was over 1000cm on rotated grain crop fields for 6 years.Required years for soil moisture of desiccated soil layers restored to local soil stable moisture by alfalfa-grain crop rotations was over 13 years.Suitable alfalfa-grain crop rotation on the semi-arid area was 7 years alfalfa and 13 years grain crops.