Direct Titration Method for Lime Requirement Estimates of Ultisols in Southeastern Vietnam

Determination of lime requirement (LR) is a routine test due to the wide use of liming materials to remediate acid soils. The titrations using several base additions reportedly work well on many soils but have not yet been tested on Ultisols (0–30 cm depth) in Southeastern Vietnam. Results showed that a titration using two base [saturated Ca(OH)2 solution] additions to 1:1 suspensions of soil in 0.01 M CaCl2 (0.10 g CaCO3 kg−1 soil per addition), a 90-min equilibrium, and a continuous shaking mode yielded reliable LR values on these soils. It estimated on average 86% of LR by the reference method and was of highest accuracy in soils with LR of around 1.58 t CaCO3 ha−1. To improve the prediction, two distinct equations were recommended for soils with LR, respectively, below and above this value. The titration under the defined conditions was likely to be suited for routine use on Ultisols in Southeastern Vietnam, with further testing, adjustment, and validation being needed.