A Brief Study on Using pH_H₂O to Predict pH_KCl for Acid Soils

Abstract

pH KCl and pH H 2 O are two basic necessary indexes to reflect the acidity of asoil. Predicting pH KCl directly from pH H 2 O could save the cost of laboratory work. In this study, the values of pHKCl and of 442 and 310 horizon samples from 126 and 98 soil profiles (0 - 120 cm in depth) surveyed from 2014 to 2015 in Guangxi and Yunnan were used to establish the optimal correlation model between pH KCl and pH H 2 O . The results showed that: 1) pH KCl is lower than pH H 2 O , pH KCl was 0.07 - 1.99 units with a mean of 0.99 units lower than for Guangxi, while 0.03 - 1.90 units with a mean of 0.89 lower than pH H 2 O for Yunan. 2) There is significant positive correlation between pH KCl and pH H 2 O , the optimal correlation models between pH KCl (y) and pH H 2 O (x) for Guangxi and Yunnan are y = 0.1963x 2 &minus; 1.0512x + 4.338, R2 = 0.836, p < 0.01 and y = 1.5882e 0.1859x , R2 = 0.769, p < 0.01, respectively, and the values of MAE and RSME of the models are 0.13 and 0.36 for Guangxi, 0.08 and 0.28 for Yunnan, respectively. There are significant negative correlations between pH KCl with exchangeable H + and Al 3+ (R2 = 0.487, 0.716, p < 0.01), and pH KCl is dominated by exchangeable Al 3+ , followed by exchangeable H + , and their contribution to pH KCl were 71.1% and 28.7%, respectively.