Research On Erosion Prevention Effect Of Large Grain Crops Covering And Estimation Of C Factor In Loess Sloping Field

Soil erosion is one of the most serious agricultural environmental problems in the world.Serious soil erosion will reduce soil fertility,degrade soil structure and thus destroy natural resource base.The Loess Plateau,which has abundant sloping farmland resources,but due to the shortcomings of steep slope,barren soil and difficult irrigation,soil erosion has become an important ecological and environmental problem to be solved urgently.The application of crop covering plays an important role in reducing soil and water loss of sloping farmland,the corresponding crop management practices in the growing period of crops will also disturb the surface and change the surface conditions to a certain extent,therefore,its impact on soil erosion is related not only to the crops themselves,but also to the surface changes formed under the management practices.In the Universal Soil Loss Equation(USLE),cover and management factor is an effective index to quantitatively evaluate the inhibition effect of crop cover and management measures on soil erosion.The cover management factor(C-factor)has become one of the most sensitive and complex parameters in the universal soil loss equation(USLE)because of its sensitivity to anthropogenic activities.C-factor estimation is a key part of soil erosion prediction model,which in-depth study is helpful to further prevent and control soil and water loss in sloping farmland.Presently,there are a lot of models for predicting the C factor value through coverage,which is only one of the indicators characterizing the aboveground crops.Alternative C-factor estimation approaches considered vegetation coverage alone,which can not involve the belowground crops(such as roots),the impact of soil properties affecting crop growth(such as soil bulk density which reflects soil physical properties)and possible surface changes under management practices(such as surface roughness,soil crust which reflect soil micro topography and surface structure)on soil loss.This can decrease the accuracy of the estimation to an extent.In this study,soybean and maize,the main large grain crops in slope farmland in the Loess Plateau,were taken as the research objects,several cropping systems were established to investigate the coupling effect of surface changes under different management practices and crop cover in preventing soil loss at the plot scale.Five experimental(CP,cropped;SSR,roughened;SC,crusted;CP-SSR,cropped-roughened;CP-SC,cropped-crusted)plots were set,compared to bare plot(BP).The impact of cropping systems on soil loss was estimated by SLR(soil loss ratio),according to the universal soil loss equation(USLE).The SLR estimation models were provided via identifying the related sub-factors,subsequently,combined with the distribution curve of rainfall erosivity to allow the novel C-factor estimation.Our study provides a new idea for further clarifying the anti-corrosion law and threshold of crop covering and management practices,and carrying out national C factor research.The main conclusions are as follows:(1)Through the study on the initial time to runoff(ITR)and Initial loss of rainfall(ILR)of different cropped treatments(CP),it was found that under the two rainfall intensity and the slope gradient of 3°,5°,10° and 15°,ITR and ILR of cropped plot were greater than those of bare land(BP).Moreover,under the two rainfall intensity,ITR and ILR gradually increased with the advance of growth period.Under the condition of 40mm/h,maize has the same law as soybean;under the condition of 80mm/h,there was no obvious change law with the growth period advancing.The total amounts of runoff and sediment of cropped plots(CP)in the whole growth period were positively correlated with slope and rainfall intensity.According to the analysis of soil and runoff reduction capacity order of different cropped treatments,it was found that Maize covered plot>soybean covered plot.With the advancement of crop growth period,the abilities of runoff and soil loss reduction were gradually enhanced.(2)It was found that under the two rainfall intensities and 3°,10°,15° slope conditions,ITR and ILR of roughened plot(SSR)were greater than those of bare land(BP);under 5°slope condition,ITR and ILR of roughened plot(SSR)were smaller than those of bare land(BP),and the greater the rainfall intensities,the smaller the difference.Under 3°、5°、10°、15° slope conditions,ITR and ILR of crusted plot(SC)were smaller than those of bare land(BP).The existence of soil crust will significantly advance the runoff time,and the existence of surface roughness will delay the runoff time.The greater the slope and rainfall intensities,the larger the total amounts of runoff and sediment of management treatments.According to the analysis of soil and runoff reduction capacity order of different management treatments,it was found crusted plot(SC)>roughened plot(SSR).(3)Under the slope gradient of 3°,5°,10° and 15°,ITR and ILR of cropped-roughened plot(CP-SSR)were greater than those of bare land(BP),ITR and ILR of cropped-crusted plot(CP-SC)were less than those of bare land(BP).The total amounts of runoff and sediment of cropped-management practices(CP-SSR、CP-SC)in the whole growth period were positively correlated with slope and rainfall intensity.According to the analysis of soil and runoff reduction capacity order of different cropped-management practices,when compared two different crop variables,soybean covered-roughened plot>maize covered-roughened plot,soybean covered-crusted plot>maize covered crusted plot,but the soil and runoff reduction capacity were similar in the later periods of crop growth.When compared surface changes formed under two different management practices,cropped-roughened plot(CP-SSR)has stronger runoff reduction capacity than cropped-crusted plot(CP-SC).The regulation of soil reduction capacity was complex,except that maize covered-roughened plot>maize covered-crusted plot under the condition of 40mm/h rainfall intensity,the soil reduction capacity of cropped-crusted plot(CP-SC)was stronger than that of cropped-roughened plot(CP-SSR).(4)Taking the change law of SLR of“crop covering" test groups under the condition of 100 slope gradient and 80mm/h rainfall intensity as an example,SLRCP>SLRCP-SSR>SLRCP-sc.The coupling treatments of cropped and roughened or crusted have better anti-erosion effect than single cropped measures.Compared with SLRCP,when it comes to“crop covering" test groups with soybean as the test object,SLRCP-SSR decreased by 12.42%,35.04%,25.98%,13.41%,respectively,with an average decrease of 21.71%from the early flowering to the initial seed-forming growth period.SLRCP-SC decreased by 25.22%,44.85%,34.89%,47.47%,respectively,with an average decrease of 38.11%from the early flowering to the initial seed-forming growth period.When it comes to“crop covering" test groups with maize as the test object,SLRCP-SSR decreased by 21.21%,2.19%,4.92%,15.25%,respectively,with an average decrease of 10.89%from the early jointing to the tasseling growth period.SLRCP-sc decreased by 18.96%,1.43%,20.26%,19.42%,respectively,with an average decrease of 15.02%from the early jointing to the tasseling growth period.(5)According to the analysis of relationship between bulk density,cover crop and SLRCP in different growth period,it was found that soil bulk density and SLRCP was obviously relevant.But there was no obvious change law of soil bulk density index with the development of crops.With the advancement of crop growth stage,the crops crown width increased,the stem developed,and the root density grew vigorously.There was a very significant negative correlation between above-ground crop indicators(coverage,CC;plant height,pH),below-ground crop indicators(root weight density,RDw;root surface area density,RDsa;<0.5mm root length density,RDL1;all in 0-0.5cm soil layer)and SLRCP(p<0.01).Further analyzed the relationship between roughness parameters and SLRCP-SSR,crust parameters and SLRcP-SC,the results showed that the initial surface roughness(Cr0)decreased gradually,the initial crust thickness(Tc0)increased gradually,with the advancement of crop growth period.There was a significat positive correlation between Cr0 and SLRCP-SSR(p<0.05).Moreover,there was a a significant negative correlation between Tc0 and SLRCP-SC(p<0.05).(6)The existing C-factor estimation formulas of crop sloping field lacked parameters which can reflect the influence of soil properties(e.g.,bulk density),below-ground crop(e.g.,root system)and surface changes(e.g.,surface roughness and soil crust)formed by management practices,so it is impossible to comprehensively and systematically evaluate the C-factor value.This study screened out the crop coverage(CC),plant height(pH),0-5cm soil layer root parameters(root weight density,RDw;root surface area density,RDsa;<0.5mm root length density,RDL1),and initial roughness(Cr0),initial crust thickness(Tc0)as the key parameters,then,based on USLE model,the new C-factor estimation model which suitable for the Loess Plateau was established.Compared with the existing C-factor estimation formulas of crop sloping field,the new models can achieve more accurate simulation result.It was approved that the C-factor estimation involved multiple parameters has higher feasibility.