Evaluation of the Effectiveness of a New Method of Measuring the Chemical Reactivity of Liming Materials on Two Acid Soils from Zambia

ABSTRACT

There is currently no quick available method for assessing chemical reactivity of liming materials used to neutralize soil acidity. This study was conducted to assess the effectiveness of a method developed to determine the chemical reactivity of liming materials. The reactivity of five conventional liming materials, biochar, charcoal and wood ash was determined using the method. Liming materials were applied to surface samples of two Ultisols at rates intended to neutralize exchangeable acidity. Physico-chemical and mineralogical properties of liming materials and soils were determined. Soils treated with the liming materials were incubated for 12 weeks in plastic containers using a soil: water ratio of 1:1. The pH and exchangeable acidity of the samples were measured every fortnight. The reactivity of the conventional liming materials was found to be strongly and positively (r = 0.99) correlated with their calcite contents, and strongly and negatively (r = −0.98) correlated with their dolomite contents. Strong positive linear relationships (R² ≥ 0.79, p < .05) were observed between the reactivity and mean pH of the two soils between the 2nd and the 12th week, while strong negative linear relationship (R² ≥ 0.79, p < .05) was observed between the reactivity and mean exchangeable acidity of the soils. Conventional liming materials were better than biochar and charcoal in neutralizing acidity. The new method was effective in predicting the ability of liming materials to neutralize exchangeable acidity and to raise the pH of acid soils. It can be used by farmers and lime producers to assess the reactivity of liming materials.

KEYWORDS:

• Agriculture lime
• Calcite
• Dolomite
• Chemical reactivity
• Soil pH
• Exchangeable acidity