紫色土区草篱根系对其根-土复合体抗剪和抗冲性能的影响

The effects of grass hedgerow roots on shear strength and scouring resistance of root-soil complexes in the purple soil region

为探索草篱在紫色土坡地的水土保持价值及其根系固土的力学性能特征,在重庆市北碚区"西南大学紫色丘陵区坡耕地水土流失监测基地"种植了2种草篱(紫花苜蓿和拉巴豆),定量研究了草篱根系形态、纤维含量、抗拉特性以及根-土复合体的抗剪/冲性能,明确了根系对其根-土复合体抗剪/冲性能的影响及主要影响因素。结果表明:1)紫花苜蓿和拉巴豆根-土复合体中有超过90%的根系直径小于1.0 mm,紫花苜蓿根系的纤维含量较高,拉巴豆根系的根长密度、根表面积密度、根体积密度较优;2)同一径级下根系平均极限抗拉力和抗拉强度均表现为拉巴豆(19.76 N,32.70 MPa)>紫花苜蓿(14.32 N,26.66 MPa)。极限抗拉力与根系直径呈幂函数正相关,抗拉强度与根系直径呈幂函数负相关;3)2种草篱根系均能显著提高根-土复合体的粘聚力和抗冲指数(P<0.05),尤其是拉巴豆。拉巴豆根-土复合体平均粘聚力达22.88 kPa,较对照提高了71.06%,最大抗冲指数达19.00 L·g^(-1),是对照的2.60倍;4)主成分分析表明根系通过根长密度、半纤维素含量以及极限抗拉力来影响根-土复合体的抗剪/冲性能,拉巴豆草篱根-土复合体抗剪/冲性能的综合得分均高于紫花苜蓿草篱。综上,紫色土坡地上拉巴豆草篱根-土复合体抗剪/冲性能显著优于紫花苜蓿草篱。

Vegetated contour strips have significant effects on soil and water conservation on slopes,and the plant roots play a very important role. To explore the soil conservation properties of their root systems,we planted strips of two legumes(Dolichos lablab and Medicago sativa) at the Southwest University,Chongqing and the shear strength and scouring resistance of root-soil complexes were tested. To identify factors affecting mechanical properties,we imaged roots in grayscale,tested root chemical composition and mechanical properties and subjected data to correlation analysis. It was found that:1)More than 90% of the root-soil complexes of M. sativa and D.lablab had a root diameter of less than 1. 0 mm. The cellulose content of M. sativa complexes was significantly higher than that of D. lablab. The root length density,root surface area density and root volume density,and shear strength of complexes of D. lablab were more than those of M. sativa. 2)For the same diameter,the average maximum tension and tensile strength of D. lablab root complexes(19. 76 N and 32. 70 MPa,respectively)were more than those of M. sativa(14. 32 N,26. 66 MPa). The root diameter was positively correlated with ultimate maximum tension by a power function,and negatively correlated with tensile strength by power function. 3)The root systems of the two legume vegetation strips significantly(P<0. 05) improved the cohesion and resistance,especially D. lablab vegetation strips. The average cohesion of D. lablab complexes was 22. 88 kPa,which was71. 06% higher than that of the CK. And the scouring coefficient of D. lablab complexes was 19. 00 L·g;,2. 60 times of that of the CK. 4)Principal component analysis showed that the root system traits that most affected the shear strength and scouring resistance of root-soil complexes were root length density,hemicellulose content and maximum tension. The comprehensive score of root-soil complexes of D. lablab vegetation strips was higher than that of M. sativa. In summary,the shear strength and scouring resistance of root soil complexes of D. lablab vegetation strips were better than those of M. sativa strips.