黄土坡耕地退耕还林后土壤性质变化研究

退耕还林是治理黄土高原水土流失的根本措施。论文以退耕历史较长的黄土丘陵沟壑区安塞县为例,选取不同类型植被恢复和不同恢复年限的退耕样区,探讨了退耕还林还草对土壤理化性质的影响。结果表明,坡耕地退耕后,遭侵蚀破坏的土体构型渐趋恢复,土壤容重、pH值减小,毛管孔隙度、饱和含水量等增大;土壤有机质增加了2.75倍,碳增加了27.29%,氮增加了46.79%;而且,土壤速效养分增加的速度大于土壤全量元素增加的速度。土壤质量恢复效益最大的是刺槐林地,其次是柠条灌木地,最小的是撂荒地。混交林土壤全氮含量最高,柠条最利于铵态氮、硝态氮和亚硝态氮的积累。不同类型植被,土壤速效养分的差异比土壤全量元素间的差异明显。随恢复时间的增加,土壤结构不断得到改善,土壤有机质、全碳、全氮以及主要离子含量呈明显增加趋势,土壤速效养分增加更明显。土壤有机质在植被恢复5年以上开始明显增加,土壤碳、氮和速效养分则在10年以后增加明显。

Research on Soil Quality Change after Returning Farmland to Forest on the Loess Sloping Croplands

Soil and water loss is very serious in the Loess Plateau.Converting farmland to forest or grassland is key to control soil erosion.The samples were collected at the Ansai county of Shaanxi province in China,and according to survey of the abandoned land for restoring different plant species with different restoration time,soil samples from depth intervals of 0～20cm were collected for laboratory assessment to analyzing their soil physiochemical properties.The effects of farmland conversion to forest or grassland on soil quality in the loess hilly field were studied.The results showed that soil quality significantly improved after conversion of farmland to forest or grassland.When compared to sloping farmland,vegetation restoration has resulted in significant reduction in soil bulk density and pH,and increases in soil porosity,optimum soil moisture,soil organic matter,soil carbon,nitrogen,and available soil nutrients to differing degrees.Robinia pseudoacacia has contributed most to soil quality restoration,caragana korshinskii kom comes the second,and wasteland the least.In the same time,with the increase of abandoned time,soil texture was increasingly improved,and soil organic matter, carbon,nitrogen,and available soil nutrients occurred an increasing trend.Meanwhile,the available soil nutrients increased much more than the soil elements.Thus,returning farmland to forest or grassland can not only effectively control soil erosion,but also significantly restore soil quality.