Study On Soil Capability Of Nutrient's Holding And Soil Degradation In Karst Area In Southwest China

The ecosystem of karst is vulnerable.She is of compatibility of advantages and disadvantages of environmental factors,diversity and rigor of habitat,inhomogeneity and accompanying attributes of water's deficit,vulnerability of environment and hard to improve.So,it would be an important and significative work to study soil degradation and capability of nutrient's holding in karst area.This paper analyzed characteristics of the soil fingerprint charge and soil nutrient retention capacity in different karst rocky desertification;and chose three karst regions(that is natural ecologic rehabilitation region,man-made ecologic rehabilitation region and region had not project) to compare soil nutrient retention capacity;at the same time,analyzed soil physical and chemical properties which sampled in man-made ecologic rehabilitation region one year later,put forward that if we work out atlases of soil fingerprint charge in prior period,we can query soil nutrient retention capacity just through soil pH;finally,this paper sampled soil in a camphor slope,through analyzed on soil nutritive elements,like that Ca,Mg,Cu,Zn,Mn,Mo,Si,Fe,we had a deeper understanding with soil ground erosion and underground soil leaks.pH is the main soil variable,and it also is the main impact factor to symbol and quantity of soil varying charge.At the same time,pH is a crucial property of soil,and soil physical and chemical properties,activity of microbe,growth of plants would be change when pH varied.So,we can evaluate soil capability of nutrient's holding.Soil fingerprint Charge(SFC) is a method to measure charge characteristics of soil surface which is determined by ion strength of soil.i.e.measure maximum capability of keeping ion in different pH and ion concentration.SFC has its special characters in different area,or soil types,like as people's fingerprint,so we called it soil fingerprint charge.Compared to non-karst area,SFC was more efficiency in illustrated soil capability of nutrient's holding:We had many dates about SFC in different land use in karst area and non-karst area, like that dry land,wasteland,and woodland.And found that in all of land use in both area,the SFC which corresponded by its intrinsic pH was in moderate standard.The reason was fertilization in dry land.In wasteland,compared with non-karst area,B soil layer had a low SFC corresponded by its intrinsic pH,and indicated in karst area,after soil degradation,the speed of soil renew was slowly.To sum up,SFC was more efficiency in illustrated soil capability of nutrient' s holding.In karst area,it was different to obtain soil samples between karst area and non-karst area.In karst area,because of the influences from the alkali rocks,we must avoid when sampling:We analyzed coefficient of variation(CV) of soil pH where soil was in round of or away from alkali rocks.It was indicated that in a one soil vertical section,the CV of pH was greater than 2%,and alkali rocks had big influence to soil pH,especially in 20 centimeters to alkali rocks.For example,in soil geologic section of camphor woods, surface soil pH of alkali rocks was higher about 0.14 pH units to 20 centimeters offscale of alkali rocks,and compared to topsoil,was higher about 0.24 pH units.In pinus massoniana soil vertical section,there were more differences,like that o.5 pH units,and the CV was 5.11%.In honeysuckle soil vertical section,soil pH of in 20 centimeters of alkali rocks was 7.15,and 7.05 in 20 to 40 centimeters,so there were a difference about 0.1 pH units.Due to the method of SFC mainly applied to non-karst area,and had different characters about pH to karst area,so we must modify the pH grads.Analyzed by dates, and founded that:In China karst area,soil pH mainly focused between 5.0 and 8.0.So, we amended soil pH grads to(8.0,7.2,6.4,5.6,4.8,and 4.0),the reasons as follows:Soil pH and soil growth were on speaking terms.In karst area,due to abound of Ca²⁺,and soil pH show to neutral or tiny alkalescence,like that:in Anhui karst area,the pH was 6.15 to 8.06;in Chongqing,in Beibei Jigong Mountain,the pH was 5.98 to 8.00; in Wushan,the pH was 5.68 to 8.51;in Qianjiang,was 5.18 to 7.69;in Jifo mountain, was 4.25 to 6.95;in Yangshang in Guangdong,the pH was between 7.0 and 8.06,and so on.So,I expanded the upper limit of soil pH.In Jinfo Mountain,according to soil features,the soil section can be divided into no karste rocky desertification,week karst rocky desertification,middle karst rocky desertification,and strong karst rocky desertification.It was found that under different degree of karst rocky desertification(KRD),it shows clear change about SFC,i.e., under no KRD,the range of soil pH,which keeps nutrient,is consistent with real pH. Under week KRD,the capacity of keeping nutrient in layer B is similar to layer A under no KRD,and the capacity of layer A was disturbed.Under middle and strong KRD,pH of layers A and B is decreased to be acid,which is possibly due to fertilization by land use.The fulvic acid contained more active functions groups compared with humic acid, and therefore had more positive correlation on SFC,and humic acid had more negative correlation.So,it is significant which used SFC to evaluate soil capability of nutrient's holding and forecast soil degradation.This paper analyzed soil fingerprint charge and the degradation of soil structure, moisture,micro-carbon and fertility,then obtained conclusions in three different research areas,that is Jigong Mountain—natural ecologic rehabilitation 15 years region, Nanping Town -- ecologic rehabilitation by changing land-use region 1 year ago, Dongsheng Town - region had not project.Finally,we can find that:there were no soil degradation in Jigong Mountain;Nanping Town had light soil degradation,and the optimal land-use was vivacious Huajiao Forest.And after period of time by ecologic rehabilitation,soil quality may improve;and Dongsheng Town had medium soil degradation,if it was still in no rule in land-use,all of indexes wound become serious. Base on soil fingerprint charge,the ranking of soil degradation in three areas was: Dongsheng Town＞Nan ping Town＞Jigong Mountain and it held on the line with conclusion one.Exampled on Shiqing village in Nan ping town,relative analyzed soil physical and chemical properties in one year in different land use,then,draw a conclusion:after restoring the reclaimed land,uncultivated wild grassland had an advantage over fir or camphor woods,and in favor of improve soil degradation,because there were a relatively rapid growth of nutrient.In man-made ecological restoration,prickly ash peel woods was the best land use,and had a good capability to hold nutrient.Secondly was honeysuckle and peach tree wood.So,in poor karst area,in order to link environmental benefits,eco-efficiency and social and economic efficiency,it were best measures to plant prickly ash peel or honeysuckle.It can improve capability of holding nutrient in short phase.,also it were beneficial to soil fertility,and hold back soil erosion.Sampled soil in a camphor slope,through analyzed on soil nutritive elements,like that Ca,Mg,Cu,Zn,Mn,Mo,Si,Fe,we had a deeper understanding with soil ground erosion and underground soil leaks.It indicated that:from peak to bottom of slope,there was a varying degrees process about soil erosion.But it was strange that in the bottom of slope,there were not deposit obviously in ground,so it must be existed underground soil leaks.This was different to other red or yellow soil area,because of double deck structure(ground and underground:like as cracks,sinkholes,and so on) in karst area.In studied area,the content of Mg,Cu,Zn,Mn and Mo changed at middle slope, turned up to inflection point,so,we can think that from middle to bottom of slope,there was a function about ground soil erosion and underground soil leaks.And the content of Si,Fe and Ca had an inflection point in foot slope.