Effects Of Rock Fragments On Soil Infiltration Processes In Karst Mountains Region Of Northwest Guangxi, China

Rock fragment (diameters>2mm) are usually covered on surface soil of dolomiteareas of Northwest Guangxi, China; and its soil also contains large amounts of graveland Laminated rock fragments (LRF). The present of rock fragment indicates soildegradation, and changes soil physical and chemical properties as well. Consequently,process of soil water movement is modified. Therefore, to study the effect of rockfragment on soil infiltration processes of karst areas is very important for study onwater cycle mechanisms and vegetation rehabilitation, and hydrological response.In this study, water infiltration process of different gravel coverage, rock fragmentcontents, sizes and laminated rock fragments are studied through columns of disturbedsoil samples. And we also use disc permeameter diagram to test the process of soilinfiltration. The main results are as following:1)When LRF (gravimetric soil-stone content:50%) was located in the upperposition (0-20cm) with a bigger size (20～40mm), it could suppress the soilinfiltration processes and its cumulative infiltration capacity is the smallest. WhenLRF was located in the middle position(0-20cm)with a smaller size (5～20mm), itcould be benefit for the soil infiltration processed, but when LRF was located in themiddle position (0-20cm) with a bigger size (20～40mm), it could suppress the soilinfiltration processes. When LRF was located in the lower position, it had little effecton soil infiltration processes.2)The cumulative infiltration capacity was the biggest when LRF was located inthe middle position (10-30cm) with the size of5-20mm during0to120minutes;And the cumulative infiltration capacity was the smallest when LRF was located inthe upper position (0-20cm) with the size of5-20mm during0to120minutes.However, when it was located in the lower position (20-40cm), the cumulativeinfiltration capacity reached the biggest with the size of20-40mm. 3)The cumulative infiltration capacity showed a trend from decrease to increasewhen the thickness of LRF (LRF was located in10-30cm and with a size of20～40mm, and gravimetric soil-stone content:50%) was increase from0to40cm; Thecumulative infiltration capacity was the smallest with a thickness of20cm of LDF.The results showed a trend of "decrease-increase-decrease" for the cumulativeinfiltration capacity when the gravimetric soil-stone content of LRF increased from0to50%.4) When the size of rock fragment is5～20mm, the cumulative infiltrationcapacity showed a trend from decrease to increase with increasing of the gravimetricsoil-stone content from0to50%during0to140minutes; The cumulative infiltrationcapacity was the smallest with a gravimetric soil-stone content of30%. When the sizeof rock fragment is20～40mm, the cumulative infiltration capacity showed a trend of"decrease-increase-decrease" with the increasing of the gravimetric soil-stone from0to50%; The cumulative infiltration capacity was the smallest with a gravimetricsoil-stone content of50%.5)The cumulative infiltration capacity had a trend of increasing when the rockfragment coverage (0,18%,32.2%,53.7%) increased. When the rock fragment wascompletely embedded in the soil (0-5cm) and the gravimetric soil-stone was greaterthan5%, the rock fragment was benefit for soil infiltration processes. When the rockfragment was covered on soil surface, its cumulative infiltration capacity was biggerthan no-stone soil and rock fragment which was completely embedded in the surfacesoil.6) There was a poin of intersection for the cumulative infiltration and sorptivetycurve of abandoned land (included rock fragments) and coin's (no-stone) surface soil.When infiltration began, the cumulative infiltration and sorptivety of abandoned landwere bigger than coin field's. This situation was opposite after the produing of thepoint. The cumulative infiltration and sorptivety of abandoned land were shorter thancoin field's. But when the negative pressure was-5cm, the cumulative infiltration ofabandoned land and coin surface soil was no significant. The infiltration rate andapproximate hydraulic conductivity of abandoned land were both shorter than the coinfield's.7) The infiltration cumulative and infiltration rate, and sorptivety, andapproximate hydraulic conductivity of the coin field' surface soil were both biggerthan the brush land. But when the the negative pressure was-1cm, the two had a point of intersection, the sorptivety of the coin field was bigger than the brush land's.