Study On Spatial Variability Of Soil Nutrients In Early Stage Of Rocky Desertification Control In Baishao River Watershed

The rocky desertification in Karst region is a major obstacle to restrain the economic development and people’s living standard,and the soil fertility is an important basis for rocky desertification control.The watershed as a relatively complete sink unit basically covers most of the terrain conditions and hydrological processes.Based on the scale of watershed,it is possible to objectively reveal the comprehensive driving effect of terrain,hydrology,land use and other factors on the spatial variability of soil nutrients by studying the spatial variation of soil nutrients.The small watershed of Baishui River is a typical karst peak pond landslide.Broken terrains,complex landforms and spatial distribution of soil show a high degree of spatial heterogeneity.The change of land use pattern is accompanied by the changes of ecological factors and soil nutrients.Based on terrains,land use and vegetation types,soil samples of 0-5cm,5-10 cm and10-20 cm soil layers were collected and the soil organic carbon(SOC),total nitrogen(TN),total phosphorus(TP),total potassium(TK),available nitrogen(AN)and available kalium(AK)were measured.The horizontal spatial variation rule and vertical changing of soil nutrient was analyzed by the combination of geostatistics and GIS.The effects of soil parenting,topography and land use on spatial variation of soil nutrient were discussed.The correlation analysis and principal component analysis were used to analyze the soil nutrient,and the spatial distribution of soil fertility was plotted.And the soil fertility status under different land use patterns was analyzed.The following are the main research results:(1)The variability of soil nutrient in the study area was between 46.95% and 82.50%,which was moderate variation.The variability was the highest in total phosphorus,and the lowest in available nitrogen.The difference between organic carbon and total nitrogen,and the variability of total nitrogen was greater than that of available nitrogen,and the variability of total potassium was greater than that of available potassium.Organic carbon,total phosphorus and available potassium showed a strong spatial self-phase,mainly affected by natural factors.The spatialautocorrelation of soil layer in 0-5 cm is strong,5-10 cm is moderate,and 10-20 cm is weak,and the influence of human factors is increased with the deepening of soil.The spatial autocorrelation of soil total potassium is very weak,and it tends to develop in a same direction,which is mainly affected by human factors.The range of soil nutrient is between 169 m and 3996 m.The spatial autocorrelation range is large,which showing that total potassium is the largest one,organic carbon and total nitrogen are the second,and total phosphorus,available nitrogen and available are the smallest.(2)The content of soil organic carbon in the study area is high,and the high value area is mainly in the northeast of the basin,and the distribution area is larger and the content of the south is lower.The content of total phosphorus in the soil is low,which is sporadic patchy distribution.The high and low values are intertwined.The high value areas are mainly concentrated in the north and middle parts,and the low value area is mainly in the south.The total nitrogen content is moderate,and the content of available nitrogen is very rich.The distribution of total nitrogen and available nitrogen of soil layer in 0-5 cm and 5-10 cm is similar,with higher content in the north and middle parts,and lower in western and southern parts.In the10-20 cm layer,the total nitrogen content is the highest in the north and the area of the high value area is larger.The effective nitrogen is gradually increasing in the middle and the northeast and southwest.The total potassium content is at a very low level and the content is the lowest in the middle of the basin.From the middle to the west and east,the content gradually increased.The available potassium content is moderate,and the distribution trend is high-low-high-low from north to south.(3)The contents of soil organic carbon,total nitrogen,total phosphorus,available nitrogen and available potassium in dolomite development were the highest.Except the effect of potassium,in the contents of other nutrient indicators,limestone was the second,sand shale was the lowest,potassium is the same amount of sand shale,limestone content is the lowest;total potassium in the limestone under the highest content,the lowest in the sand shale.The results showed that the soil nutrient index of limestone was decreased with the increase of soil layer,and the soils developed by sand shale decreased with the increase of soil layer.The soil nutrient index of dolomite developed with the rule of changing is not obvious.The effects of slope on soil organic carbon had significant effects on total nitrogen and available nitrogen,obvious effect ontotal phosphorus,little effect on total potassium and available potassium,and were negatively correlated with total potassium relationship.Organic carbon,total nitrogen and available nitrogen increased with the increase of slope,and the changing of total phosphorus,total potassium and available potassium did not change with slope.The contents of organic carbon,total nitrogen and available nitrogen were higher in sparse woodland,shrub land and natural grass,and the content of total phosphorus was the highest under natural grass.The content of total phosphorus was the highest in masson pine forest,and the content of available potassium in the cultivated land and cherry forest land is higher,the content of the natural grass is lower,the total potassium content in the sparse forest is the lowest,and the effective potassium is the lowest in the underground of masson pine forest.(4)There was a highly significant or significant positive correlation among organic carbon,total nitrogen,available nitrogen and total phosphorus.The correlation between available potassium and other soil nutrients was small,and the correlation between total potassium and other soil nutrients was the smallest.The areas with high soil fertility in the watershed were mainly distributed in the northeast,which showed the high-low-high-low trends from north to south.Low-lying areas of fertility is low,the area of higher fertility is higher.The order of soil fertility under different land use type as follow: sparse wood> shrub land> cherry woodland>farmland> abandoned land > natural grassland> Pinus massoniana forest land.Therefore,Pinus massoniana forest land with low soil fertility although the species Pinus massoniana is the major species for afforestation.