Experimental Study On The Effect Of Roots On Soil Impact Resistance During Growth Of Typical Grasses In Loess Area

The Loess Plateau is an ecological fragile area in China and soil erosion is serious. As the vegetation root is active factors between root and soil, it has an active impact on soil anti-scouribility. Because of special climate and soil properties of the Loess Plateau, "Returning Farmland to Forest and Grassland" policy should not just blindly afforestation, should pay more attention to grass vegetation restoration and ecological reconstruction. A large number of studies had focused on the macro natural environment, and many complex factors in natural environment will have multiple effects on the research result, causing a larger error, bring great obstacles to the research. This study research soil anti-scouribility of ryegrass(Lolium perenne L.) and alfalfa (Medicago sativa L.) change's rule at different planting density, different growth stages and different soil layers by indoor simulation experiment.Discuss the effect of plant roots on soil physicochemical properties and soil anti-scouribility, and provide a theoretical basis of soil erosion control and ecological construction of the Loess Plateau. The research obtains the following conclusions:(1) Investigate the status of root in different growth periods and different soil layers. The growth of ryegrass with high planting density is inhibited, while for the growth inhibition of alfalfa is not obvious. With the increase of growth period, increasing each root density on the whole processing. High planting density of ryegrass with increase of growth period, fine root gradually reduced and thick root increased gradually; root density of alfalfa changed a little in four growth stages. The size of root density of Ryegrass:surface soil layer> subsurface soil layer>bottom soil layer. The root of ryegrass mainly in the surface soil layer, and it is difficult to influence to the deeper soil layer. The main root effect of alfalfa is on surface soil layer and subsurface soil layer, root density decreases gradually with the increase of soil depth.(2) Study on the physicochemical properties of different growth periods and different soil layers. In different growth period, soil bulk density of ryegrass decreased with the increase of growth time; but soil bulk density of alfalfa change a little. The soil organic matter of ryegrass increased with the increaseof growth time, the size of soil organic matter in three growth periods is HR (high planting density ryegrass)>LR (low planting density ryegrass); the soil organic matter of alfalfa have a little change but lower than the soil organic matter of ryegrass. With the increase of the growth time of ryegrass, soil water stable aggregates increased gradually; soil water stable aggregates of alfalfa is increased slowly and then decreased. In different soil layers, with the increase of soil depth, soil bulk density of ryegrass and alfalfa increased gradually; effects of ryegrass on the surface soil bulk density is larger. Ryegrass soil organic matter, the size of soil water stable aggregates in each layer is surface soil layer>subsurface soil layer>bottom soil layer, soil organic matter and soil water stable aggregates of alfalfa decreases with the increase of the soil depth.(3) Investigate the erosion process of each soil layer, soil anti-scouribility at different growth stages and different soil layer. In each soil layer, soil erosion in per unit time is maximum at the 5min. The soil erosion of ryegrass in per unit time on the surface layer is minimum and in a stable state; because alfalfa have lower root density, soil erosion in per unit time is at a high level. The size of soil anti-scouribility index: ryegrass> alfalfa>CK.With the increase of the growth time, the enhancement effect of ryegrass with the high planting density on the soil anti-scouribility could not be improved obviously, and the fluctuation of soil anti-scouribility enhancement rate of alfalfa is not big.The size of soil anti-scouribility index of Ryegrass is surface soil layer> subsurface soil layer>bottom soil layer. Ryegrass have a greater effect on soil anti-scouribility index of surface soil layerand little effect on the subsurface and the bottom soil layer. The soil anti-scouribility index of HR is larger than LR, alfalfa with high planting density can significantly improve the soil anti-scouribility in subsurface soil layer.(4) Discuss the relationship between soil anti-scouribility, soil physicochemical properties and roots. There was a positive correlation among each root parameters of ryegrass and alfalfa. The soil bulk density of ryegrass showed a extremely significant negative correlation with the root density, while the soil bulk density of Alfalfa showed a significant negative correlation with the root surface area density and root volume density.There is a extremely significant positive correlation betweens soil water stable aggregates and the each root density of ryegrass; no correlation between soil water stable aggregates and each root density parameters of alfalfa. The soil organic matter of ryegrass showed a extremely significant positive correlation with each root density parameters; soil organic matter of alfalfa showd a extremely significant positive correlation with root length density, a significant positive correlation with root surface area density and root weight density. Soil anti-scouribility index of Ryegrass increase exponentially with the the increase of root density parameters; root density parameters and soil anti-scouribility index of alfalfa was not related. Roots of D?5mm of Ryegrass have a greater impact on soil anti-scouribility; and alfalfa root length density and root surface area density of 0<D<0.1mm,1.0<D?2.0mm and D>5.0mm have a significant correlation with soil anti-scouribility index. Soil anti-scouribility of Ryegrass show a power function relationship with soil bulk density, a exponential relationship with soil organic matter, and a power function relationship with soil water stable aggregates; there is no correlation between soil physicochemical properties of alfalfa and soil anti-scouribility index of alfalfa.By the regression analysis with stepwise method, the anti-scouribility index equation of ryegrassis:ASI=5.626RWD-0.126T+2.651, P<0.01.