Calculation Of Soil Erodibility Factor (K) On A Global Scale And Analysis Of The Effect Of Rock Fragments On Soil Erodibility Factor

Soil erosion is one of the worldwide environmental problems,which poses a great threat to the healthy development of ecological environment and social economy,and is the inducement of many other environmental problems.In the prediction model of soil erosion,soil erodibility factor（K）usually represents the effect of soil properties and soil profile characteristics on soil loss.USLE-K,RUSLE2-K,EPIC-K and Dg-K are four widely used methods for calculating soil erodibility factor（K）.However,it remains to be studied which algorithm is more suitable to calculate soil erodibility factor（K）in the global scale.While,soil erodibility factor（K）is mostly calculated based on soil physical and chemical property data,which does not involve the content of rock fragments in these algorithms.However,the amount of rock fragments and thier distribution difference have a certain influence on soil physical and chemical properties,and then affect the accuracy of the estimation of soil erodibility factor（K）.In this paper,USLE-K,RUSLE2-K,EPIC-K and Dg-K algorithms were used to estimate global soil erodibility factor（K）,and its spatial pattern and main controlling factors were analyzed.In this paper,the measured data of soil erodibility factor（K）were retrieved by literature retrieval method,and the measured database of K factor value was established.The rationality of the results of the above four algorithms was analyzed,and the above four algorithms for calculating K factor were modified according to the measured database of K factor.At the same time,USLE-K algorithm is taken as an example to calculate the effect of rock fragments in the soil profile,the effect of rock fragments on the surface and the combined effect of rock fragments in soil profile and rock fragments on the soil surface,and the influencing factors of the relationship between stoniness and erodibility were analyzed quantitatively and formed a systematic understanding.（1）The spatial pattern of global K values obtained by the USLE-K,RUSLE2-K,EPIC-K and Dg-K models is similar,but the calculated values are slightly different.The mean values of the four algorithms are 0.0296,0.021,0.0269 and 0.0275,respectively.The K values calculated by the four algorithms,especially the first three algorithms,all show a spatial pattern of high K values in western North America,Western Europe and central Asia,and low K values in eastern South America,southern Africa and The Continent of Australia,but the specific values are slightly different.The results based on Dg-K algorithm are slightly different from those of other three algorithms.The results of the main control factor analysis showed that the main control factor of the K factor obtained by USLE-K,RUSLE2-K and EPIC-K was the silt content,and the sand content was the main control factor of the K factor obtained by the Dg-K algorithm.（2）Comparing the 106 measured values,the mean value of RUSLE2-K algorithm is the closest to the measured K factor value,followed by the USLE-K algorithm and the EPIC-K algorithm,and the Dg-K algorithm is quite different from the mean value of measured K factor.Comparing the 106 measured values with the K factors obtained by the four algorithms,it is found that there are certain deviations in the estimation accuracy of the four algorithms on a global scale,but they can be corrected.The revised results can be better used for global soil erosion assessment.（3）The presence of rock fragment in the soil profile reduced the saturated water conductivity of soil,increased the soil permeability,and increased the global soil erodibility factor by 2.84%.The rock fragment on the soil surface reduces soil erosion by protecting soil from raindrops and runoff,and in mountainous and desert（desert and gobi）areas,this effect reduces soil erodibility by 18.7%.The combined effect of rock fragments in profile and rock fragments on the surface reduced soil erodibility factor by 6.98%.The soil erodibility factor could be reduced by 0.0051（t.hm².h）/（hm².MJ.mm）in the area mainly affected by rock fragments on the soil surface.The soil erodibility factor increased by0.0008（t.hm².h）/（hm².MJ.mm）in the area dominated by rock fragments in soil profile.（4）The relationship between stoniness and erodibility(R_S-K)is affected by a variety of environmental factors,among which,elevation and slope steepness are positively correlated with R_S-K(the effect coefficient of rock fragments on the soil surface（St）,the effect coefficient of rock fragments in soil profile(K_cf)and the combined effect coefficient of rock fragments on the soil surface and rock fragments in soil profile(K_f-cs)).Vegetation coverage,annual mean precipitation and annual mean temperature were negatively correlated with St and K_f-cs.The annual mean precipitation was negatively correlated with K_cf.The effect of rock fragment of sunny slope is greater than that of shady slope.The effect of rock fragment of cultivated land and forest land is small,while that of grassland,desert and bare land is large.The main controlling factors of St and K_f-cs are elevation and slope steepness,and the main controlling factors of K_cf are perennial annual mean precipitation and annual mean precipitation.