Influence And Assessment Of Conversion Of Ecosystem Types On Soil Fertility In Guizhou Karst Mountain Area

In order to ascertain the influence of conversion of ecosystem types on soil fertility and soil quality in Guizhou karst mountain area,five kinds of ecosystem types(woodland,artificial grassland,natural grassland,cropland and derelict land)under different altitude gradients were chosen as research objects,and by means of the methods of field sampling and laboratory analysis,the variation characteristics of soil bulk density,soil porosity,pH value,soil CEC,soil organic matter,total nitrogen contents,total phosphorus contents,total potassium contents,alkali-hydrolytic nitrogen,available phosphorus,available potassium,available ferrum,available manganese,available copper,available zincum,available molybdenum and available boron of five different kinds ofecosystem types were studied.Furthermore,the soil fertility qualities at different elevation were evaluated comprehensivelyby principal components analysis,and the effects of conversion of ecosystem types on soil fertility qualities were analyzed.The main results were as follows:(1)At various altitudes,when woodland changed intoartificial grassland,soil bulk density increased by 1.53% to 14.40%,porositydecreased by 1.30% to 11.70%;soilpH value reduced 11.17% to 28.03%;soil CEC diminished by 10.00% to 37.33%;soil organic matter declinedby 4.15% to 54.84%;in the soil layer depth of 0 to 10 cm and 10 to 30 cm,soil total nitrogen content of woodland was lower than that of artificial grassland,but in the soil layer depth of 30 to 50 cm,soil total nitrogen content of woodland was more than that of artificial grassland;under different altitude gradients,soil total phosphorus contents elevated generally;in the soil layer depth of 0 to 10 cm and 10 to 30 cm,soil total potassium content of woodland was lower than that of artificial grassland,and in the soil layer depth of 30 to 50 cm,soil total potassium content of woodland was higher than that of artificial grassland;the content of soil alkali-hydrolytic nitrogen enhanced by 6.70% to 35.55%;under different altitude gradients,contentsof soil available phosphorus and available potassiumboth raised;contentsof soil availablecopper,available zincum,available ferrum and available manganese alldecreased;at low altitudes,the content of soil available molybdenumincreased,but in middle and high elevation area,the content of soil available molybdenum decreased;in middle elevation area,the content of soil available borondeclined remarkably.(2)At various altitudes,when natural grassland changed intocropland,soil bulk density decreased by 3.31% to 16.22%,porosity increased by 3.33% to 24.64%;soilpH value reduced 1.29% to 11.02%;soil CEC diminished by 6.43% to 54.70%%;soil organic matter declinedby 17.14% to 40.60%;soil total nitrogen content increased by 15.15%-159.29%,total phosphorus contentelevated by 104.17% to 182.35%,total potassium content declined by 18.90% to 45.00%;the content of soil alkali-hydrolytic nitrogen enhanced by 13.15% to 117.03%,available phosphorus increased by 62.56% to 303.51%,available potassium dwindled by 9.69% to 25.23%;content of soil availablecopper increased by 18.99% to 46.00%,available zincum declined by 3.45% to 30.29%,available ferrum decreasedby 24.54% to 33.45%;content of soilavailable manganeseenhanced at low altitudes,and dropped in middle and high elevation areas;content of soilavailable molybdenumenhanced at middle altitudes,and dropped in low and high elevation areas;the content of soil available boronincreased generally.(3)At various altitudes,when cropland changed intoderelict land,soil bulk density increased by 1.37% to 27.42%,porositydecreased by 9.96% to 24.36%;soilpH valueraised by 0.04% to 13.79%;soil CEC added by 17.08% to 63.44%%;in the soil layer depth of 0 to 10 cm,soil organic matter declinedby 40.93%at low altitudes,and in middle and high elevation areas enhanced by 9.13% and 17.61%,respectively;soil total nitrogen contentabated by 10.37% to 82.82%,total phosphorus declined by 24.49% to 65.45%,total potassium increased by 18.45% to 32.27%;the content of soil alkali-hydrolytic nitrogen reduced by 12.98% to 66.83%;content of soil available phosphorusdiminished in low and middle elevation area,but raised at high altitudes;content of soil available potassium increasedby 8.92% to 26.92%;content of soil availablecopper dropped by 26.21% to 48.84%,available zincum decreased by 3.06% to 40.56%,contentsof soil availableferrum,manganese,molybdenum and boron alldecreased.(4)The results of principal components analysis showed that at low altitudes the sequence of scores of soil fertility of different ecosystem types was woodland?artificial grassland ? natural grassland ? derelict land ? cropland,at middle altitudesthe sequence was woodland ? natural grassland ? artificial grassland ?cropland?derelict land,and at high altitudes the sequence was natural grassland?cropland?woodland?derelict land?artificial grassland.Research results indicated that the conversion of ecosystem types has exercised a profound impact on soil fertility and soil quality in Guizhou karst mountain area,and it has profoundsignificance to protect soil environment and to utilize soil resourcesreasonably for the improvement of fragile ecological environment and for the sustainable development of the social economyin this area.