本研究采用野外试验和室内分析相结合的方法，以陕西省渭北高原草类及作物植被 为研究对象，重点对植被的不同空间部位(冠层、根层)的水土保持效益以及不同部位 在水力侵蚀过程中的作用进行了研究，取得如下结论： 一、植被类型不同，水土保持效益亦不同。草类植被防止水力侵蚀的作用要明显大 于作物植被，在试验雨强下，草类植被拦蓄径流和泥沙的效益均在90％以上，而作物植 被只能达到60％以上。其中拦蓄径流的效益从大到小依次为：苜蓿>荒草>玉米>豆子； 拦蓄泥沙的效益从大到小依次为：苜蓿>荒草>豆子>玉米。 二、植被冠层、根层对水力侵蚀的调控作用受植被类型的影响。对于草类植被，冠 层的作用较小，拦蓄径流和泥沙的效益都不到5％，其根层起主要调控作用，拦蓄径流 和泥沙效益均在90％以上；对于作物植被， 冠层的作用增加，拦蓄径流效益在10％以 上，拦蓄泥沙效益在50％以上，根层的作用下降，拦蓄径流效益下降为50％左右，拦蓄 泥沙效益黄豆为31．23％，玉米只有3．76％。 三、植被冠层、根层在侵蚀过程的不同阶段所起的作用是不同的。在产流过程中： 豆子根层的作用始终远大于冠层；玉米则是在产流的起始阶段和发展阶段，根层的作用 大于冠层，但是在消退阶段，冠层的作用略大于根层。而且，对于这两种作物植被来讲， 根、冠作用比在整个产流过程中都有逐渐降低的趋势。在产沙过程中：豆子是在起始阶 段，根层的作用较冠层大，随着产流的延续，冠层、根层的作用都在逐渐增大，到了消 退阶段，根层的作用只是略大于冠层，整个产沙过程中根、冠作用比也有逐渐降低的趋 势；玉米则是冠层的作用始终大于根层。 四、水力侵蚀过程中泥沙以细颗粒相对富集为特征，导致坡耕地表层土壤结构变差， 质地变粗，肥力下降而退化，而植被可以在一定程度上阻止土壤中较细颗粒的流失，防 止土壤粗化。本次试验选用的两种作物植被中，豆子较玉米能更好的改善土壤质地。

In this research．on the basis ofthe studies indoom and field．researches were carded out to study benefit of soil and water conservation and function in water erosion process of the layersofcanopyand rootofgrassand cropvegetationonWeibei PlateauofShaanxiProvince， following findings Can be reached： Firstly,tapes of vegetation lead to the difference of benefits of soil and water conservation．The research results show that grass vegetation carl more effectively control water erosion than crop vegetation．The benefits for grass vegetation reducing surface runoff and sediment ale above 90％，as well aS the benefits for crop vegetation are above 60％in test rainfall intensity．The sequence of the benefit for reducing surface runoff．" Clover>Grassland>Com>Bean plant；the sequence of the benefit for reducing sediment： Clover>Grassland>Bean plant>Corn． Secondly，tapes of vegetation influence the regulation of the layers of canopy and root in water erosion process．For grass vegetation，the function of root is greater than canopy．The benefits of canopy for reducing surface runoff and sediment are below 5％．while the benefits of root are above 90％．For crop vegetation．there have been an increase of the function of canopy,and the benefit of canopy for reducing surface runoff is above 1 0％，the benefit for reducing sediment is above 50％．The benefit ofroot for reducing surface runoffis above 50％， the benefit of Bean’S root for reducing sediment yield by 3 1．23％，the benefit of Core’S root for reducing sediment yield by 3．76％． Thirdly,the layers of canopy and root play different roles in different stages of erosion process，With delay ofrunoff-yield time，the function ofroot is greater than canopy for Bean； the function of root is greater than canopy for Corn in both initial and developmental stage， but the function of root is less than canopy for Corn in final stage of erosion process．Both for the two crop vegetation，the function proportion of root to canopy drop off in whole runoff-yield process．With delay of sediment-yield time，the function of root is greater in initial stage，then the function of canopy and root increase with the development of runoff-yield，but the function of root is slightly greater than canopy in final stage of erosion process for Bean，and the function proportion of root to canopy also drop off in whole sediment-yield process，whereas the function of canopy is greater than root for Corn in whole sediment-yield process． Fourthly,the sediment of eroded field richly gather fine particles in erosion process， which lead to an increase of coarser soil particle proportion．However,vegetation Can improve soil mass，and make all increase of fine soil particles to avoid becoming coarse fur soil．Bean call make better soil mass than Corn ofthe crop vegetation in our test．