A rapid procedure to calculate lime requirements based on single titration with base

Abstract

The lime requirement (LR) in 39 surface acid soil samples (0–30 cm) from western Greece was calculated using a single-addition titration of successive 3-mL 0.022 M calcium hydroxide [Ca(OH)₂]. Soil pH measurements and titrations were performed in soil/water (1:2) and in a soil/0.01 M CaCl₂ (1:2) suspension while being stirred. The results were referred to as ‘pH data group I’ and ‘pH data group II’, respectively. In each ‘pH data group’, the samples were separated into ‘pH data subgroups’, according to the total volume (mL) of 0.022 M Ca(OH)₂ added to increase the initial pH (pH_a) to a target value of 6.5 (pH_t). The fitted linear regression equation pH_t = b × volume + pH_a was used for each ‘pH data group’ to determine the slope b. The b-weighted mean for each ‘pH data group’ was calculated. The LR was then calculated as follows: Mg CaCO₃ ha⁻¹ = 0.495 (pH_t – pH_a)/b, where b is the average weighted mean from the two ‘pH data groups’ and is equal to 0.227. The validity of the above equation was confirmed after incubation with Ca(OH)₂ for 72 h. This procedure is simple and gives a rapid and accurate estimation of LR with respect to the environment.

Keywords:

• lime requirements
• soil acidity
• titration