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 a
significant role in that promoting soil development, improving soil physical and chemical
properties and the reducing of the soil erosion. In the paper, soil physical and chemical
properties were measured after a profound field survey so as to determine the effect of
biocrusts on soil efodibility (soil erodibility factor K value) with different composition and
biomass of biocrusts soil in the typical Hilly Loess Plateau region. We calculated the K
value of soil with different composition and biomass biocrusts by using the EPIC model
firstly. 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 soil
erodibility, which would likely provide scientific basis to the mechanism of soil
antierodibility improvement by biocrusts and to the establishment of Soil Erosion Model
that take the biocrusts as an influence factor in Hilly Loess Plateau region.The main results
are as follows.
(1) Biocrusts influenced on soil physical and chemical properties, significantly. The
development 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 crust
and mix crust (mosses coverage was about 65%) were higher than that of caynobateria
biocrusts, significantly. When the biocrusts in the initial stage of the caynobateria biocrust to 60%-80% mosses coverage, soil coarse sand content reduced 86%, and fine sand content
increased 45%; Different types of biocrusts soil bulk density presented as that:
caynobateria > mosses > mixed biocrust; in late successional stage soil bulk density of
caynobateria biocrust reduced 15% than that in the initial stage; Field water holding
capacity and the soil porosity were performance for the mixed > mosses > caynobateria
biocrust, but in later succession stage increased 36% and 14% respectively; Soil hardness:
mosses < mixed < caynobateria biocrust, in later succession stage caynobateria biocrust
decreased 68%; cohesion: mosses > mixed > caynobateria biocrust. The cohesion of
biocrusts about six to seven times than that in bare soil; Organic matter and total nitrogen
content : mosses > mixed > caynobateria biocrust, in succession later increased 161% and
127% respectively; pH: caynobateria > mixed > mosses biocrust, along with the increase
of biomass soil pH was decreasing.
(2) Development of biocrusts significantly reduced the soil erodibility, which was
related with biomass, composition, biological activity and the soil texture.
Soil erodibility of biocrusts at the stable stage was 17% lower than subsurface soil.
Soil erodibility of biocrusts with different species composition was shown as caynobateria
crust > mixed crust > moss crust，mixed biocrust and moss biocrust decreased respectively
19% and 21% than caynobateria crust. Soil erodibility of biocrusts decreased with the
increment of biocrusts biomass. The K value of mosses biocrusts soil in the later
succession stage was 21% lower than in early succession stage. Erodibiliy of biocrusts
soils were significant difference because of the biological activities of the organisms of
biocrusts in different seasons, erodibility of biocrusts soil at rainy reason was significantly
higher than those before rainy season and after rainy season. The K value before rainy
season and after rainy season were 8% lower than that at rainy season, and there was no
significant difference between it before rainy season and after rainy season. Erodibilty of
biocrusts soil on different textures were varied significantly, and the K values were
performed in the order like sandy loam soil > silt soil > sandy soil .，and biocrusts had
great influence on erodibility of silt soil.
(3) Soil erodibility of different composition biocrusts measured by simulated rainfall
confirmed the results of the calculation by the EPIC model, which was ten times less than
subsoil (soil of 5-10 cm), which was another evidence that the development of biocrusts
can significantly reduce soil erodibility.
(4) Biocrusts significantly reduced soil erodibility mainly because of increasing the
content of soil organic matter, total nitrogen, coarse silt, soil porosity and field water
holding capacity, and decreasing soil bulk density and pH. The dominant factor of influencing soil erodibility of biocrusts was organic matter content, secondly for the
content of coarse silt, silt and total nitrogen.
The correlation analysis showed that there was a significant positive correlation
between soil erodibility and soil bulk density and pH (P<0.01), but a significant negative
correlation with silt, coarse silt, soil porosity, field water holding capacity, the content of
soil organic matter, total nitrogen content, C/N and pH (P<0.01). The content of sand had
positive correlation with soil erodibility of biocrusts (P<0.05). The results of principal
component analysis indicated that soil structure, soil particle composition and the content
of soil organic matter and total nitrogen could represent the main factor of influencing soil
erodibility of biocrusts. It showed that the main factor of influencing soil erodibility of
biocrusts was in sequence of soil organic matter, coarse silt, silt and total nitrogen by
multiple stepwise regression analysis.
Key Words：biological soil crust; species composition; biomass; soil physical and chemical
characteristics; soil erodibility