摘要
黄土高原的土壤侵蚀是我国的重要环境问题之一，一直备受关注。坡耕地是该区土壤侵蚀的重要来源，一方面制约着当地的经济与社会发展，另一方面引发下游地区洪涝灾害、非点源污染等问题。坡耕地上的农作物决定了坡耕地的生态效益和经济效益，是影响坡耕地上水土流失的关键因子，作物根系发育的好坏直接决定了作物地上部分及其产量，因此深入研究作物根系与土壤侵蚀的关系，对更好的完善坡耕地上作物功能的评价及科学生产具有重要的实践指导意义。本文以坡耕地上玉米作物及其根系为对象，采用人工模拟降雨、原状土静水崩解法、原状土冲刷法和抗剪力测定等方法，研究了玉米作物根系的产流产沙规律及玉米作物根系对土壤的抗蚀性、抗冲性和抗剪力等的影响，得出了主要结论如下：
（1）室内冲刷槽人工模拟降雨表明，坡耕地上农作物玉米及其根系皆具有一定的防蚀作用，且随叶面积指数的增加而更为显著。T1（裸地，CK）、T2（玉米根系）和T3（玉米）3种处理条件下的产流量、产沙量皆为T1>T2>T3。在产流产沙过程中，玉米可有效地延迟产流产沙时刻、峰值出现的时刻以及平和产流和产沙过程，但根系只改变了产沙过程的产沙量，弱化产沙过程的波动性作用很弱。
（2）室外径流小区人工模拟降雨表明，坡耕地上农作物玉米及其根系减水减沙效益良好。相对T1（裸地，CK），T2（玉米根系）和T3（玉米）两种处理的拦蓄径流率分别为16.74%和54.17%，拦截泥沙率分别为47.74%和79.66%，结果皆为T2 （3）玉米作物根系可以提高土壤的抗蚀性。在裸地处理下，土壤崩解速率随着土层深度的增加而减慢，二者呈负相关关系；在玉米的各个生长阶段，玉米根系生长情况不同，对土壤抗蚀性的影响大小不同。在0-10cm土层，玉米根系最大时可使抗蚀性增强约45%，10-20cm土层最大时可增强32%。土壤崩解过程相对祼地稳定，且达到稳定的时间短。
（4）玉米作物根系对土壤的抗冲性影响显著。在祼地处理下，土壤的冲前含水量与土壤的抗冲系数显著相关。在玉米根系处理下，土壤的冲前含水量对玉米根系土壤的抗冲系数具有一定的影响但不显著；而玉米根系的干重与其土壤抗冲系数呈显著相关。在冲刷作用后，玉米根系处理下的土壤含水量相对祼地处理下较均匀。
（5）土壤抗剪力与土层深度呈正相关，与坡度呈负相关。在农作物玉米各生长阶段，玉米根系处理的各个土层的土壤抗剪力皆大于裸地。综合分析4个坡度下，土壤中有玉米根系存在的小区平均抗剪强度较裸地可增强21.34%。
Soil erosion is paid more and more attention in the Loess Plateau, as one of importantenvironment problems in China. Cultivation on sloping land is the major source of soilerosion of the Loess Plateau, which is one of the main factors in limiting the developmentof economy and society in local area. On the other hand, cultivation on sloping landthreatens the security in downstream area due to flood and non-point pollution. Cropsdetermine the economic benefit and ecological benefit, as the key factor of influence on thesoil and water loss. The root growth of crops affect the crop aerial part and yield. Thus, toimprove the estimation of crop function and to operate agricultural production scientifically,the relationship between crop root and soil erosion were studied. In our study, the laws ofrunoff and sediment caused under the cover of corn on plot were studied, as well theinfluence of corn root on soil anti-erodibility, soil anti-scourability and soil shearingresistance were studied, which were conducted by using rainfall simulating experiment,hydrostatic disintegrating method the undisturbed soil trough scouring method anddetermination of shear resistance. Main results are as follows:
1. Under the rainfall simulating experiments on the soil bins, we found the corn androots had the erosion resistance, with the erosion resistance increasing as the leaf area indexincreasing. The runoff varied as the following order: T1(CK)>T2(Corn root)>T3(Cornplant), the sediment varied as the same pattern. During the process of generating of runoffand sediment, corn plant can delay the times of generation and peak values of runoff andsediment, while corn root only affect the sediment yield slightly.
2. Under the rainfall simulating experiments on the field runoff plots, results showedthat both corn plant and corn root played a positive role in reducing runoff and sediment.The efficiency of runoff and sediment reduction under the T3treatment is higher than thatunder the T2treatment, which agrees with the results under the rainfall simulatingexperiments on the soil bins. The runoff are16.74%and54.17%lower in the T2and T3treatments compared to the T1treatment respectively, while the sediment are47.74%and79.66%lower in the T2and T3treatments compared to the T1treatment respectively.
3. Corn root can improve the soil anti-erodibility. The relationship between soil disintegration rate and soil depth in the T1treatment (CK) is negative, with the soildisintegration rate declining as the soil depth increasing. Besides, the influence of corn rooton the soil anti-erodibility varied with the growth of corn root during different growthstages. Corn root can increase the soil anti-erodibility up to45%approximately in the0-10cm soil layer, with32%for the10-20cm soil layer. The process of soil disintegration issteady, of which the time to remain steady is shorter compared to the ones under the CKtreatment.
4. The influence of corn root on soil anti-scourability is significant. The relationshipbetween soil water pre-wash and soil anti-scourability coefficient is significant in the CKtreatment. The relationship between soil water pre-wash and soil anti-scourabilitycoefficient is not significant in the corn root treatment, while the relationship betweenamount of corn root and soil anti-scourability coefficient is significant. The soil water ismore homogeneous in the corn root treatment than the one in the CK treatment.
5. The relationship between soil anti-scourability and soil depth is positive, while therelationship between soil anti-scourability and slope angle is negative. During each corngrowth stage, The soil anti-scourability of different soil layers is stronger under the cornroot treatment than the one under the CK treatment.
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