High negative surface charge increases the acidification risk of purple soil in China

•Richer mineral composition induces high content of surface charges on purple soil.•Purple soil contains large amount of Al3+ after electrodialysis treatment.•Purple soil has a deeper degree of acidification than variable charge soils. Purple soils, developing from rapid physical weathering of nutrient rich sedimentary rock and classified as Inceptisols or Entisols in United States Department of Agriculture (USDA) Taxonomy, are the most important agricultural soils in the Sichuan basin of southwestern China. A portion of purple soils has been acidified and the acidification risk of these soils need further understanding. Here, electrodialysis (ED) was used to simulate the process of natural acidification of soils. We investigated the acidification risk of purple soils by ED treatments and compared its acidification characteristics with that of variable charge soils (Oxisol and Alfisol). Our results showed that the degree of acidification of purple soils after ED treatments was much higher than that of variable charge soils, although the purple soils contained more exchangeable base cations. There was no significant correlation between the purple soil acidity before and after ED treatments, however, the pH of purple soils after the ED treatments had a significant negative correlation (r = −0.680, P