PRELIMINARY STUDY ON ACIDITY AND ACIDIFICATION SENSITIVITY OF FLUVO-AQUIC SOILS OF NORTH CHINA PLAIN

Fluvo-aquic soils in North China Plain were collected for the preliminary investigation of their acidity characteristics and acidification sensitivity,under intensive agricultural utilization.Soil pH significantly correlated with nitrate,which indicated that overuse of nitrogen fertilizer was the important driving factor for soil pH decline.Dissolution of CaCO3 is the main acidification buffer process in these fluvo-aquic soils.Soils with lower CaCO3 were sensitive to the acid input with fast pH drop,while soils with higher CaCO3 were insensitive to continuous acid input.Critical acid buffer capacity,acid buffer intensity and pH buffer intensity,calculated based on acid-base titration curve,positively correlated with CaCO3 content.Such relationships clearly showed the strong dependence of acidification sensitivity on soil carbonates.Depletion of soil carbonates induced by intensive utilizations will result in,in turn,faster decrease in soil pH,which brings potential risk to soil quality and environment health.Methodology improvement on acidification sensitivity assessment,with enough consideration to the buffering characteristics,is the most urgent task in the regulation of acidification in fluvo-aquic soils.