English abstract
Soil pH is the most common property needed for soil assessments. Determination of pH assists in understanding many reactions that occur in soil. Measured values of soil pH can be affected by procedure used for determination and a range of soil properties. In this study, pH was measured in different electrolytes (distilled water (pHw), 0.01MCaCl2 (pHca), IMKCI (pHk), and 0.01 MBaCl2 (pHba)] with different soil: electrolyte ratios (i.e. 1:1, 1:2.5, and 1:5). The main objective was to determine the effect of each electrolyte and dilution ratio on pH of saline and non-saline soils from Oman. It was found that pH values varied significantly between electrolytes and with different dilution ratios. Variation values of pH determined in different electrolytes were significantly correlated.
pH values measured in water were highly affected by suspension effect and gave significant differences between different dilution ratios. Other electrolytes (CaCl2, KCI and BaCl2) were not affected by suspension effect and they gave approximately stable values when pH measured under stirring and non-stirring condition. pH values were significantly different in term of dilution effect but not higher than pH measured in water. Electrolytes, especially KCI, seemed to be well correlated with other soil properties such as %clay, cation exchange capacity (CEC), electrical conductivity (EC) and calcium carbonate (CaCO3), and less affected by other interference such as salts present in soil.
Water is a highly suitable solvent for soil pH measurements because it is simple, values are understandable, and most people are familiar with its explanation. However, alkaline errors and instabilities, due to liquid junction and soluble salts effect, during measurements can not be avoided when pH measured in water.
Soil salinity affected pH measurements, especially in water, and resulted in relatively unstable readings during pH measurements. Variations were minimised when pH was measured in other electrolytes rather than in water. In this study, a negative relationship was found between soil salinity and pH. The main factor contributing to this relationship was probably the presence of Ca'' ions, which had a negative relationship with soil pH and positive relationship with soil salinity. Other soil properties such as CEC, CaCO3 and sodium adsorption ratio (SAR) were also accounted,
Linear regression equations were generated between electrolytes, dilution ratios and soil properties. Most equations showed a good relationship between each other with high R' values. Measurements done in water and KCl were found to be highly correlated to calcareous soils and can help in predicting soil pH with other soil properties. The major variables that can be used in prediction of soil pH were CEC, CaCO3, SAR, and soluble Ca and Na.
