| The karst areas in southwest China are characterized by large area,wide distribution,complex topographic conditions,rapid soil erosion,high bare rock rate and shallow soil layer,which are typical fragile ecosystems.At the same time,the region has a large population and intense human activities,resulting in a great risk of rocky desertification.Therefore,restoring and maintaining the ecological environment in this area is of great significance to the environmental and ecological construction in Southwest China.The physical,chemical and biological properties of soil play a decisive role in the restoration and construction of ecological environment in Karst areas.So,the physical,chemical and biological properties of karst soil and their influencing factors have attracted the attention of researchers.As an important basic property of soil,soil physical,chemical and biological properties are significantly affected by five factors of soil formation,such as parent material,climate,biology,topography and time,and human activities.At present,the effects of parent material type,rocky desertification degree,vegetation composition,land use pattern,topography and man-made measures on physical,chemical and biological properties of karst soil have been studied.Although topographic factors do not directly affect the related properties of soil,they can affect the physical,chemical and biological properties of soil by influencing the redistribution of parent material,water,light and biological factors.It has been found that topographic factors such as slope,aspect and elevation have significant effects on the physical,chemical and biological properties of soil organic matter,soil enzyme activity,soil water content,bulk density and saturated hydraulic conductivity.Rock stratum tendency is one of the three elements to describe the occurrence of rock stratum in the spatial position of rock stratum,and it is also one of the topographic influencing factors.Different landform types are formed by the combination of strata tendency and different slope directions,such as the bedding slope(which is consistent with the inclination of rock stratum and slope surface)and the reverse slope(which is opposite to the inclination of rock stratum and slope surface),which have a direct impact on the surface morphology and rock outcropping.Previous studies have shown that the location and fragmentation degree of rocks exposed in Karst peaks and clusters have a significant impact on soil moisture content in different parts,so different rock strata tendencies will affect soil water content infiltration by affecting rock location.Soil moisture is an important factor affecting the transport and transformation of substances in soil.The more soil moisture is,the longer it lasts,the more favorable it is for the leaching of substances in soil,thus affecting and changing the physical,chemical and biological properties of soil.Therefore,different strata tendencies will affect soil water content and thus affect the spatial variability of soil physical and chemical properties,but at present,there is no research report on the effect of strata tendencies on soil physical and chemical properties.In this paper,soil physical,chemical and biological properties such as soil natural water content,soil leaching index,soil basic element content,soil nitrification and denitrification capacity,soil salt-based ion exchange capacity,soil basic nutrients were studied by stratified sampling at Longche Village in Beibei,Chongqing,Hexin Zanthoxylum bungeanum base in Youyang,Chongqing and Yinjiang Langxi Valley in Guizhou Province.The following results were obtained for the effects of soil physical,chemical and biological properties on sloping farmland:1.The combination of rock stratum tendency and slope direction has a significant effect on the physical properties of karst slope farmland.The natural water content of the bedding slope was higher than that of the reverse slope in the three study areas.In Youyang soil,the soil bulk density of the bedding slope is lower than that of the reverse slope,and the soil pore condition is better than that of the reverse slope.2.The soil chemical properties of sloping farmland show some regularity changes under the combination of rock stratum tendency and different slope directions.Soil organic matter,total nitrogen,total phosphorus,total potassium,alkali-hydrolyzed nitrogen,available potassium and other soil fertility indicators in the three study areas were higher or significantly higher than those in the reverse slope,and the pH value was lower or significantly lower than that in the reverse slope.The content of total Ca in the downward slope was lower than that in the reverse slope,and the contents of total Fe,total Mn,total Ti and total V in the downward slope were higher than those in the reverse slope.The relationship between the content of available phosphorus in the downward and reverse slopes of the three regions is not clear.The salt-based ion exchange capacity of sloping farmland soil is quite different from that of rock strata under different slope direction combinations.The soil exchangeable K content of Sloping Farmland in the three study areas was little affected by rock stratum tendency,and there was no significant difference between the bedding and reverse slopes.Exchangeable Na,exchangeable Ca and exchangeable Mg contents were significantly affected by strata tendency.Exchangeable Na and exchangeable Ca contents in the soil along the bedding slope were significantly higher than those in the reverse slope,and exchangeable Mg contents were lower than those in the reverse slope.Soil nitrification and denitrification in the bedding slope were significantly stronger than that in the reverse slope.The soil nitrification and denitrification capacity of the bedding slope in the three study areas were higher or significantly higher than that of the reverse slope.3.The preliminary results of correlation analysis and principal component analysis showed that soil moisture content was the main factor affecting the changes of physical,chemical and biological properties of Sloping Farmland in the three regions.In general,the natural water content of the bedding slope is higher than that of the reverse slope,and the pH is lower than that of the reverse slope.The leaching development of the soil is better than that of the reverse slope.The nitrification and denitrification capacity,the ion exchange capacity of the salt base and the basic nutrients of the soil are higher than that of the reverse slope.This may be due to the high rate of bare rock when the inclination of rock strata is the same as that of slope direction,which is conducive to the accumulation and infiltration of water into the soil around bare rock,increasing the water content of the corresponding soil,and promoting the leaching and development of the soil.The results of this study lay a foundation for further study of the effects of rock strata orientation and slope combination on the properties of karst soil. |
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