玉米和大豆根系对滇中地区坡耕地红黏土抗剪强度的影响

Effects of Maize and Soybean Roots on Topsoil Shear Strength of Red Clay on Sloping Farmland in Central Yunnan

水土流失是限制山区坡耕地持续利用的主要问题。为探讨农作物根系固土机理,采用无侧限压缩试验测定了素土、玉米和大豆成熟期根土复合体的抗剪强度和应力应变特性,WinRHIZO(Pro.2019)根系分析系统测定了根系构型特征,分析了根土复合体力学特性与根系特征参数间的关系。结果表明:(1)玉米和大豆根系能显著增强土体抗剪强度(P<0.01),其根土复合体强度相对素土分别提高了117.65%和71.91%;(2)两种农作物根土复合体黏聚力c与根长密度、根表面积密度、根体积密度、根重密度均呈极显著正相关(P<0.01),其中D≤1mm细根对黏聚力增量Δc的贡献大于其他径级根系;(3)根系构型性状中,玉米根分支数高于大豆45.44%且各径级根系分布更均匀,其根土复合体随含根量的增加,在破坏时表现出弱应变硬化特征且裂缝拓展变缓,侧向变形减小。综上农作物根系均能增强土体抗剪强度,但根系结构类型不同则对土体力学特性的影响不同,细根和分支数较多的玉米根系更能有效增强土体强度和约束变形,因此须根系玉米对表层土体的固持能力优于直根系大豆。坡耕地利用中,可以通过合理布局须根系农作物来防治水土流失。

【Objective】The area of sloping farmland in central Yunnan accounts for 61.14% of the total arable land area, and its sustainability is affected by serious soil erosion. Thus, it is urgent to study the positive effects of the rational allocation of vegetation on the sloping land space on improving soil erosion and maintaining sustainable agricultural production. About 89.4% of the sloping farmland utilization in the province is for planting crops, and maize and soybean are the main crops in summer. Previous studies have shown that the soil-fixing capacity of vegetation roots plays a significant role in soil and water conservation. This study was conducted to explore the soil-fixing effect of corn and soybean roots and to provide a basis for the calculation of the soil-fixing ability of crop roots. 【Method】In this study, a field experiment was designed to have three treatments and a total of 9 experimental plots;i.e. CK(Bare land), MM(mono-maize) and SS(mono-soybean). The unconfined compression tests were used to determine the shear strength and stress-strain characteristics of rootless soil and root-soil composites of maize(Zea mays L.) and soybean(Glycine max L.) at the mature stage. The WinRHIZO(Pro.2019)system was employed to analyze the root distribution and configuration characteristics. And then the relationship between shear strength and root parameters was studied.【Result】The results indicated that:(1) Compared with rootless soil, the roots of maize and soybean significantly enhance the shear strength of root-soil composite(P<0.01), and the strength of the root-soil composites was increased by 117.65% and 71.91%, respectively;(2) The cohesion of two crop root-soil composites were significantly positively correlated with root length density, root surface area density, root volume density, and root weight density(P<0.01). Also, the contribution of fine roots with D≤1 mm to the cohesive force increment was greater than that of other diameter-level roots;(3) In the different root architecture traits, the number of root branches of maize was 45.44% higher than that of soybeans, and the root distribution of each diameter class was more even. The corn root-soil complex showed weak strain-hardening characteristics when the root content was increased. Also, the crack propagation slowed down and the lateral deformation decreased.【Conclusion】The root systems of the two crops could enhance the shear strength of the soil.However, the different root structure types demonstrated different effects on the mechanical properties of the soil. The maize root system with more fine roots and more branches can effectively enhance the strength and restrain the deformation. Thus,fibrous root maize is better than taproot soybeans in holding the surface soil. In the use of sloping farmland, it is possible to prevent soil erosion by rationally arranging fibrous root crops. This study provides a reference for the rational layout of crop planting to prevent soil erosion on slope farmland.