Study on driving factors of soil acidification based on grey correlation-structure equation model

Abstract

【Objective】 Soil pH is an important indicator of soil fertility and also a factor significantly impacting crop growth and production. Soil acidification, as a result of the joint effects of a number of external and intrinsic factors, has become an urgent problem to solve for sustainable development of agricultural production in China. How these factors affect soil acidification differ significantly in pathway and effect. It is, therefore, of critical significance to elucidate region-specific key driving factors of soil acidification to the control of soil acidification and improvement of soil quality. 【Method】The study set Fujian Province as its research object. Based on the 1:50 000 spatial cropland and soil type databases of the province, the data of topsoil properties of the 36 777 sampling sites investigated in 1982 and the 56 445 sampling sites in 2016, and other relevant data including climate elements at the meteorological stations, pH of the precipitation at the acid rain monitoring points and fertilizer application rates from 1982 to 2016 in Fujian Province, a spatial database of cropland soil acidification and its potential affecting factors of the province was established. On such a basis, in-depth discussion was performed of key driving factors of cropland soil acidification in the province during the period from 1982 to 2016 with the aid of the grey slope correlation (GSCM)-structure equation (SEM) model. 【Result】Results show that soil pH of the cropland had decreased on average by 0.34 unit and 70.67% of the cropland soils had been acidified in various degrees by 2016 in Fujian Province, and the acidification varied significantly and spatially in degree. GSCM analysis shows that the main driving factors of the cropland soil acidification in Fujian Province included annual mean fertilizer application rate, CEC, clay content, annual mean precipitation, annual mean pH of the precipitation and organic matter content. Grey correlation coefficient of their absolute values was higher than 0.620. The key driving factors of the cropland soil acidification illuminated by SEM included severe acid rain, high precipitation and high application rate of chemical fertilizers, reaching 0.38, -0.40 and -0.70 in direct effect, 0.11，-0.35 and -0.16 in indirect effect, and 0.49, -0.75 and -0.86 in total effect, respectively.【Conclusion】The model of SEM-GSCM proves to be a better method to explore for key driving factors of cropland soil acidification in different regions. An effective approach to control of cropland soil acidification in Fujian is to control acid rain through controlling the industry from emitting acidic exhaust gas, and optimize fertilizer management through extrapolating the use of organic manure to minimize chemical fertilizer application in agriculture.