Evaluation of distilled water pH measurement with electrolyte methods in cultivated soils of Nepal

Abstract

Soil pH is most routinely measured parameter among all others in soil chemistry laboratory. There are various methods developed for pH measurement, although we using only distilled water from the beginning. In Nepal, there do not have database for showing performance of the methods. The three methods namely; H2O, KCl and CaCl2 with their soil:solution ratios (1:1, 1:2 and 1:2.5) were used. The total 115 samples were collected randomly at a depth of 0-20 cm from the hill and terai regions of Nepal. The collected samples were analyzed following mentioned methods, separately. The various statistical tests (F-test, mean separation, correlation, and regression model) were performed for comparison. Moreover, model validation parameters were also calculated for relating H2O with electrolyte method. The three models linear, quadratic and cubic were used for this task. The result revealed the effect of methods on pH measurement was significantly different in the entire ratio. The pHH2O was 0.57, 0.56 and 0.67 units higher than pHCaCl2 in 1:1, 1:2 and 1:2.5 ratios, respectively. Whereas, 1.24, 0.99 and 0.95 units higher than pHKCl in respective ratio. Moreover, regarding timing to reach stable during measurement were in the order pHH2O (89.44 sec) > pHCaCl2 (54.29 sec) > pHKCl (33.08 sec). Similarly, relating modeling quadratic and cubic model showed nearly equal performance (lower RMSE, MAE and higher R2 and d) for predicting pHCaCl2 and pHKCl from the pHH2O in each soil solution ratio. The determined database can be useful for comparing used three different methods of soil pH measurement under Nepalese context.