| Soil pH is one of the important indexes to evaluate the quality of cultivated land,which is of great significance to food production safety and land productivity.In this study,Hubei Province,one of the main grain producing areas in Central China,was selected as the research area.The cultivated soil pH obtained from the second soil survey and the survey in 2017 was taken as the research object,and based on the data of topography,meteorology,crops and human activities from 1980 to 2017.Using digital soil mapping,spatial autocorrelation analysis,structural equation modeling and other theories and methods,with the help of Arc GIS,R and other software platforms,the soil pH of cultivated land was predicted.The temporal and spatial variation characteristics of soil pH in different administrative regions,different cultivated land use types and parent materials were analyzed.On this basis,the influencing factors of soil pH spatiotemporal heterogeneity were further explored,in order to provide scientific theoretical basis for the prevention and control of farmland soil acidification according to local and temporal conditions.(1)In 1980 and 2017,the soil pH value of cultivated land in Hubei Province was between 4.00-9.50 and 3.70-8.96,respectively,showing a decreasing trend from south central to east-west,and the spatial variability gradually increased from south central to east-west.From 1980 to 2017,the proportion of cultivated land samples with strong acid,acid and weak acid in topsoil increased.However,the trend of neutral,weak alkaline and alkaline farmland is opposite.Under different cultivated land use types,the pH range of paddy field changed from 4.20-9.50 to 4.00-8.96,with a decrease range of 0.08-0.73 units,and an average decrease of 0.20 units.The range of dry land pH was changed from 4.00-8.60 to 3.70-8.90,with a decrease range of 0.03-1.09 units,and an average decrease of 0.24 units.The mean value and decline unit of pH in paddy field were slightly lower than that in dry land.In conclusion,the trend of farmland soil acidification in Hubei Province in recent 40 years is obvious,which needs to be further analyzed in combination with spatial scale.(2)Among the multi-source environmental variables,13 auxiliary variables were selected to participate in the soil pH prediction mapping modeling.These variables mainly come from climate,terrain,crop and other soil forming factors.The results show that the residuals obtained by each prediction method have spatial autocorrelation,which indicates that the prediction results have the characteristics of pH local variation masked by spatial nonstationarity.Therefore,the spatial distribution of soil pH in the two periods is similar by combining residual and trend terms,using random forest Kriging,support vector machine Kriging and geographically weighted regression Kriging.During the period from1980 to 2017,soil acidification was obvious,and the pH decreased mainly in the east and north of Hubei Province.More than 50%of the cultivated soil pH value decreased from weak alkaline and neutral to acidic and strong acidic.The overall performance was that the acidification degree in the east was higher than that in the west,and the acidification degree in the north was higher than that in the south.Among them,the geographic weighted regression Kriging prediction accuracy is the highest in 1980,which is the best prediction method in this period,and the random forest Kriging method is used in 2017.(3)According to the types and regions of cultivated land use,the percentage of acidbase and acidified area of cultivated land in the whole province was calculated.The results showed that: from 1980 to 2017,the soil in each administrative region was mainly moderately acidified,and tended to develop into soil with higher acid grade.The area of acid cultivated land increased more in Wuhan and Huanggang,while weak acid cultivated land increased more in Xiangyang and Jingmen.The soil area of acid cultivated land increased by 18.5%,mainly from neutral and weak alkaline cultivated land.In terms of cultivated land use types,the proportion of cultivated land with pH < 6.5 in paddy field is larger than that in dry land,and the scope of acidification area is also larger.It can be seen that the cultivated soil in Hubei Province has been acidified to varying degrees from 1980 to 2017.(4)The percentage of acid-base and acidified area of cultivated land in the whole province was calculated according to soil parent materials.The results show that: from 1980 to 2017,the trend and degree of soil acidification of cultivated land developed by Quaternary clay sediment are the strongest,but the trend and degree of soil acidification of cultivated land developed by river lake alluvium are opposite.There were some differences in the trend and degree of soil acidification under the other parent materials,and the degree of soil acidification was mainly moderate.(5)The results showed that the total effect of each factor was different.According to the absolute value of the influencing factors,In 1980,the primary factor affecting the spatial distribution of soil pH was agricultural output(-0.28),followed by meteorology(-0.25),agricultural input(0.17),man land pressure(-0.11)and topography(0.01).In 2017,meteorology(0.24)became the main factor affecting the spatial distribution of soil pH,followed by agricultural output(0.13),man land pressure(0.05),terrain(-0.05)and agricultural input(-0.01).Therefore,agricultural output and meteorological conditions are the main factors affecting the spatial distribution of soil pH in Hubei Province.(6)The multi factor comprehensive model of soil pH spatiotemporal heterogeneity showed that: from 1980 to 2017,according to the absolute value of influencing factors,meteorology(-0.11)was the primary factor causing soil pH spatiotemporal heterogeneity in Hubei Province,followed by agricultural input(-0.07),agricultural output(-0.03)and human land pressure(-0.01).The results show that the spatial-temporal heterogeneity of soil pH in Hubei Province is a comprehensive result of the interaction of natural factors and human factors.Among them,the natural factors mainly refer to the high temperature,humid and rainy water and heat conditions,and the human factors mainly refer to the increase of nitrogen and phosphorus fertilizer,the intensive development of farmland,the increase of grain,cotton and oil production and the increase of cultivated land pressure.Therefore,according to the regional water and heat conditions and agricultural activities,we should adjust the cultivation methods,control the amount of fertilizer,add alkaline conditioner,and carry out the prevention and control of acidified soil in Hubei Province. |
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