Study On Spatial Variation And Management Zoning Of Soil PH Value Of Cultivated Land In Jiangxi Province

Soil acidification has become one of the most serious land degradation problems in southern China in recent years.The potential of Hydrogen refers to the concentration index of hydrogen ions in the soil.Small changes in pH will affect plant growth.The soil is originally a relatively stable ecosystem.Generally,the pH of the soil will be maintained within a certain range.However,with the changes of climate,topography,especially human activities,the pH of the soil will often break the stable balance and become acidified or salinization.How to clarify the spatial variability of soil pH and the influencing factors of soil acidification are the research hotspots in recent years.At the same time,the pH value of cultivated soil is one of the important indicators to evaluate the quality of cultivated land.After soil acidification,low pH value will inhibit the growth of crops,and even be out of production if the acidification is serious.The aggravation of soil acidification has seriously affected food production security in China.Therefore,the corresponding control measures are in urgent need to control the acidification of cultivated soil.However,the spatial heterogeneity of the soil determines that the factors affecting the acidification of cultivated soil in different regions are various.Hence,the introduction of the management zone solves the problem of soil acidification in different regions caused by factors provides a theoretical basis for soil acidification control according to local conditions,which provides a theoretical basis for soil acidification prevention according to local conditions.In this paper,91 counties and cities in Jiangxi Province are considered as research areas.The soil pH sampling point data of soil test and fertilization in Jiangxi Province from 2005 to 2012 is taken as the main variable,combining with auxiliary variables including the meteorological data of 88 meteorological stations in the whole province,the DEM data and the statistics of the fertilization amount in 81 counties and cities in the statistical yearbook.Firstly,all the variables are subjected to a series of preprocessing work such as outlier elimination,correlation analysis and principal component analysis in SPSS software to obtain 90805 data samples.Then these data samples are randomly divided into 80% modeling set(72644)and 20% verification set(18161 samples)in Arc GIS software.In the spatial variability study of soil pH value of cultivated land in Jiangxi Province,three prediction models are used as numerical soil mapping methods,respectively are Ordinary Kriging,Cokriging and Back Propagation Neural Network.The data of the modeling set is used as the establishing basis of the model.Besides,the data of the verification set is used to evaluate the accuracy of the three models by crossvalidation.In the research part of the management zone of cultivated soil acidification,the fuzzy C-Means algorithm based on fuzzy clustering thinking is used to demarcate the management zones of cultivated land in the province.In order to ensure the rationality of the demarcation of the partition,the Fuzziness Performance Index and the Modified Partition entropy are cited as the criteria for cluster validity test.Finally,based on the results of the management zone,combining with part of soil acidification control measures,some suggestions are put forward.The main research results of this paper are as follows:(1)The range of soil pH value of cultivated land in Jiangxi Province ranges from 3.5 to 6.8.Overall,the overall trend is low in the middle and high in the surrounding area.The high and low values shows an island-like distribution,while the median area is the dominated part.The average pH value of cultivated soil in the province was 5.1,reaching the level five acidity.Among them,84 areas are lower than the level four weak acidity,accounting for 92.3% of the province,and some regions exist extreme acidification below 4.5.The acidification situation of cultivated land in Jiangxi Province is grim and needs to be paid enough attention.(2)By means of analyzing Ordinary Kriging and Cokriging semivariogram functions of soil pH value of cultivated land in the whole Province,it could be found that the decision coefficients of the Ordinary Kriging(OK)method and the Cokriging(COK)method are 0.63 and 0.55,respectively.The lag of the OK method(17.90Km)is quite different from the lag of the COK method(27.34Km),which is related to the semivariance model of the two.The nugget effect values of the OK method and the COK method respectively are 47.83% and 66.63%,and both methods show the same level of spatial correlation.From the results,the soil property space variation is influenced by both structural and random factors.(3)Through the cross-checking method,the three indicators,separately are Mean Error(ME),Mean Absolute Error(MAE)and Root Mean Square Error(RMSE)are selected as the evaluation index of model accuracy.The three indicators of the OK method are-0.00163,0.296,and 0.409,the three indicators of the COK method are-0.00138,0.273,and 0.376,and the three indicators of the BPNN method are 0.00126,0.261,and 0.351.The comparison of the cartographic results of the three methods shows that the interpolation result of the OK method is relatively smooth in spatial structure,and the real spatial variation characteristics of the soil pH value may not be fully reflected.The interpolation result of the COK method is improved compared with OK method,and it is more detailed in some local features,indicating that the introduction of auxiliary variables increases the interpolation precision.The interpolation result of the BPNN method not only better reflects the spatial heterogeneity and randomness,but also shows higher verification accuracy than the OK method and the COK method in the cross-validation.Therefore,the BPNN method intuitively considers the spatial information of the auxiliary variables in this study,and reduces the error transmission generated in the principal component analysis,which is more advantageous in the final digital soil mapping.(4)The optimal management zone number of cultivated land soil value in Jiangxi Province obtained by fuzzy C-means clustering algorithm is 4.The degree of acidification in Zones 1 to 4 increases from light to heavy.The area with the deepest acidification has the largest area,while the first area has the lightest acidity but the smallest area.The results of the management zone indicate that the main reason for the acidification of cultivated soil is fertilization,and the effect of acid rain subsidence is weaker than the fertilization behavior.