The Effect And It's Mechanism Of Biological Soil Crusts On Soil Erodibility

Biological soil crust (biocrusts) that constituted by pioneer organismes such as algae,mosses and lichens extensively developed in the Hilly Loess Plateau region after the"Grain for Green" eco-project was implementated in the region. Biocrusts played asignificant role in that promoting soil development, improving soil physical and chemicalproperties and the reducing of the soil erosion. In the paper, soil physical and chemicalproperties were measured after a profound field survey so as to determine the effect ofbiocrusts on soil efodibility (soil erodibility factor K value) with different composition andbiomass of biocrusts soil in the typical Hilly Loess Plateau region. We calculated the Kvalue of soil with different composition and biomass biocrusts by using the EPIC modelfirstly. Then, the K value was measured by simulated rainfall under the control conditions.Results of the study suggested that biocrusts exerted a significant influence on soilerodibility, which would likely provide scientific basis to the mechanism of soilantierodibility improvement by biocrusts and to the establishment of Soil Erosion Modelthat take the biocrusts as an influence factor in Hilly Loess Plateau region.The main resultsare as follows.(1) Biocrusts influenced on soil physical and chemical properties, significantly. Thedevelopment of biocrusts could refine the soil, significantly reduce soil bulk density,hardness and pH, and increase the soil field water holding capacity, soil porosity, cohesion,organic matter content and total nitrogen content.Particle composition showed that the content of coarse silt and fine sand of moss crustand mix crust (mosses coverage was about65%) were higher than that of caynobateriabiocrusts, significantly. When the biocrusts in the initial stage of the caynobateria biocrust to60%-80%mosses coverage, soil coarse sand content reduced86%, and fine sand contentincreased45%; Different types of biocrusts soil bulk density presented as that:caynobateria> mosses> mixed biocrust; in late successional stage soil bulk density ofcaynobateria biocrust reduced15%than that in the initial stage; Field water holdingcapacity and the soil porosity were performance for the mixed> mosses> caynobateriabiocrust, but in later succession stage increased36%and14%respectively; Soil hardness:mosses <mixed <caynobateria biocrust, in later succession stage caynobateria biocrustdecreased68%; cohesion: mosses> mixed> caynobateria biocrust. The cohesion ofbiocrusts about six to seven times than that in bare soil; Organic matter and total nitrogencontent: mosses> mixed> caynobateria biocrust, in succession later increased161%and127%respectively; pH: caynobateria> mixed> mosses biocrust, along with the increaseof biomass soil pH was decreasing.(2) Development of biocrusts significantly reduced the soil erodibility, which wasrelated with biomass, composition, biological activity and the soil texture.Soil erodibility of biocrusts at the stable stage was17%lower than subsurface soil.Soil erodibility of biocrusts with different species composition was shown as caynobateriacrust> mixed crust> moss crust,mixed biocrust and moss biocrust decreased respectively19%and21%than caynobateria crust. Soil erodibility of biocrusts decreased with theincrement of biocrusts biomass. The K value of mosses biocrusts soil in the latersuccession stage was21%lower than in early succession stage. Erodibiliy of biocrustssoils were significant difference because of the biological activities of the organisms ofbiocrusts in different seasons, erodibility of biocrusts soil at rainy reason was significantlyhigher than those before rainy season and after rainy season. The K value before rainyseason and after rainy season were8%lower than that at rainy season, and there was nosignificant difference between it before rainy season and after rainy season. Erodibilty ofbiocrusts soil on different textures were varied significantly, and the K values wereperformed in the order like sandy loam soil> silt soil> sandy soil.,and biocrusts hadgreat influence on erodibility of silt soil.(3) Soil erodibility of different composition biocrusts measured by simulated rainfallconfirmed the results of the calculation by the EPIC model, which was ten times less thansubsoil (soil of5-10cm), which was another evidence that the development of biocrustscan significantly reduce soil erodibility.(4) Biocrusts significantly reduced soil erodibility mainly because of increasing thecontent of soil organic matter, total nitrogen, coarse silt, soil porosity and field waterholding capacity, and decreasing soil bulk density and pH. The dominant factor of influencing soil erodibility of biocrusts was organic matter content, secondly for thecontent of coarse silt, silt and total nitrogen.The correlation analysis showed that there was a significant positive correlationbetween soil erodibility and soil bulk density and pH (P<0.01), but a significant negativecorrelation with silt, coarse silt, soil porosity, field water holding capacity, the content ofsoil organic matter, total nitrogen content, C/N and pH (P<0.01). The content of sand hadpositive correlation with soil erodibility of biocrusts (P<0.05). The results of principalcomponent analysis indicated that soil structure, soil particle composition and the contentof soil organic matter and total nitrogen could represent the main factor of influencing soilerodibility of biocrusts. It showed that the main factor of influencing soil erodibility ofbiocrusts was in sequence of soil organic matter, coarse silt, silt and total nitrogen bymultiple stepwise regression analysis.