Root Characteristics Of Typical Vegetation On The Loess Plateau And Their Effects On Soil Detachment Process

Soil erosion includes three major processes:soil decathment,sediment transport and sediment deposition.Soil decathment provides material sources for sediment transport and sediment deposition,which can be characterized by soil decathment capacity.In the WEPP model,the measured soil decathment capacity is often used to derive the rill erodibility index and the critical shear force,which are used to characterize the ability of the soil to resist the erosion of slope runoff.However,the variety of samplers currently used to measure soil decathment capacity results in poor data comparability,and it is necessary to explore the optimal sampling size.In addition,hydrodynamic properties,soil properties,and root characteristics can also significantly affect the soil decathment process.Since the implementation of the"Grain for Green（grass）"project on the Loess Plateau in 1999,vegetation has been remarkably restored,and the topsoil properties and root system characteristics have undergone great changes,which have significantly affected the process of soil decathment.further research.Based on this,this study used the flume scouring test to systematically study the influence of soil sample width,length,shape and area on the determination of soil decathment capacity,and determined the optimal sampling specifications;the change of soil decathment capacity under different land use types was clarified The influence mechanism of hydrodynamic parameters,soil properties and root characteristics on the soil decathment process was analyzed,and the relationship between the above parameters and soil decathment capacity,rill erodibility and critical shear force was quantified,and a simulation model for the soil decathment process was established.combined equation.The following main findings were achieved:（1）The optimal sampling specification for soil decathment capacity determination was determined.Under the condition that the length of the sampler is fixed（10 cm）,the soil decathment capacity is the largest when the width is 10 cm;when the width is less than 10 cm,there is side wall effect,and when the width is greater than 10 cm,sediment deposition occurs on the slope,which all lead to soil decathment.smaller.When the width of the sampler is fixed（10 cm）,the measured value of soil decathment capacity between 5 and 10 cm in length is relatively large.Similar to the fixed length,there is side wall effect when the length is less than 5 cm after the fixed width,and sediment deposition occurs when the length is greater than 10 cm.Under the condition of the same area and different shapes,the measured value of the soil decathment capacity shows that the square is larger than the circle.The side wall effect and sediment deposition are largely related to the area of the sampler.With the increase of the area,the soil decathment capacity is a linear function.decreased（R²=0.52,NSE=0.52）,and when the soil sample area was about 100 cm²,the corresponding soil decathment capacity was the largest.Considering the effects of width,length,shape and area on the results of soil decathment,the optimal sampler size was finally determined as a square sampler with length×width=10 cm×10 cm.（2）There were significant differences in soil properties and root system characteristics under different land use types.Organic matter,bulk density,total porosity,siol cohesion,and water-stable aggregates（≥0.25 mm）in arbor woodland（Robinia pseudoacacia and Pinus tabulaeformis）,shrubland（sea buckthorn and caragana）,grassland（Leymus chinensis and Artemisia annua）,and agricultural land（millet and millet）Agglomerates vary in the range of 7.02 to 17.69 g kg^-1,0.98 to 1.16g cm^-1,50.91 to 61.03%,7.92 to 12.81 KPa and 12.92 to 70.36%.Root diameter（RD）,root mass density（RMD）,root length density（RLD）,root surface area density（RSAD）,root volume density（RVD）and specific root length（SRL）ranged from 0.036 to 0.240mm,0.55 to 3.67 kg m^-3,4.72 to 36.23 km m^-3,and 1.24 to 16.48 m² m^-3,0.0000912 to0.00294 m³ m^-3,5.14 to 18.06 m g^-1,respectively.Root characteristics were closely related to soil properties.Root mass density（RMD）was significantly positively correlated with total porosity and water-stable aggregates（P<0.01）.Root length density（RLD）was associated with cohesion and water-stable aggregates.Root volume density（RVD）was significantly negatively correlated with bulk density（P<0.05）.Specific root length（SRL）was extremely significantly positive correlation with cohesion and water stability of aggregates（P<0.01）,was significantly positively correlated with soil bulk density（P<0.05）.（3）There are significant differences in soil decathment capacity,rill erodibility and critical shear force under different land use types.The soil decathment capacity of arbor woodlands（Robinia pseudoacacia and Pinus tabulaeformis）,shrub woodlands（sea buckthorn and caragana）,grasslands（Leymus chinensis and Artemisia annua）and agricultural land（millet and millet）varied from 0.15 to 2.69 kg m^-2 s^-1.The soil decathment capacity of farmland is relatively large(2.69 kg m^-2 s^-1 for millet,1.79 kg m^-2 s^-1 for millet),1.99 to 17.93 times that of millet,and 1.33 to 11.93 times that of millet,respectively.Except that the soil decathment capacity of the pine oil plot contains turpentine and other sticky substances in the soil surface is the lowest,the soil decathment capacity of the woodland is generally higher than that of the grassland,and the highest caragana plot is 5.00 and 6.43 times of the Artemisia annua and Leymus chinensis respectively.The variation range of rill erodibility in each plot is 0.020 to0.278 s m^-1.Similar to soil decathment capacity,rill erodibility in farmland is relatively large.The overall performance of rill erodibility among land use types is the lowest except for the pine plot.The erodibility index of woodland rill is greater than that of grassland.The critical shear stress varies from 1.36 to 4.90 Pa,among which the critical shear stress of the millet and caragana plots is relatively low,and the difference of other plots is not significant.（4）Hydrodynamic parameters,soil properties and root characteristics significantly affected the soil decathment process.With the increase of water flow power,water flow shear force and unit water flow power,the soil decathment capacity decreased as a power function（R²>0.82）.Root mass density,root length density and specific root length were significantly negatively correlated with soil decathment capacity（P<0.01）.Flow power（w）,water stable aggregates（WSA）and specific root length（SRL）can better simulate soil decathment capacity(D_C=10^-1.472w^1.391WSA^-0.679SRL^-0.734,R²=0.72,NSE=0.45).Soil bulk density,water-stable aggregates and specific root length were significantly negatively correlated with rill erodibility（P<0.01）,and the above parameters could be used to better simulate rill erodibility index（R²=0.98,NSE=0.90）.In addition,the soil critical shear stress was only significantly correlated with bulk density（P<0.05）,and with the increase of soil bulk density,the critical shear stress increased exponentially（R²=0.66）.