Soil acidification process in Longjing tea field, Hangzhou

Increasing trend of soil acidification has been identified in Longjing tea field in Hangzhou. Therefore in this paper we studied the source of soil acidity and possible mechanism of acid production by mineral characterization and leaching tests. Six groups of 20 soil samples and 4 bedrock samples were collected from the tea fields. The pH value was determined by potentiometry, which was found to be stable at 4. XRD and XRF found conventional soil cations to be far lower than national soil element abundance. Dynamic leachings of soil and rock samples revealed acidity types of HNO₃ and H₂SO₄. Ca²⁺ content generated in the process of bedrock weathering was found to be relatively large and tended to leach from soil to water. Salinity cation leaching of K⁺, Ca²⁺, Na⁺ and Mg²⁺ was found to be fast and large after soil formation, which were likely the main causes of acidification. After planting tea trees for many years, the base cation leaching reduced soil base saturation, leading to reduction in soil buffer capacity therefore resulting in soil acidification.