A practical method for estimating liming requirements based on soil chemical attributes and limestone composition

The main limitations of tropical soils for food production are high acidity and low nutrient levels. When acidity is not properly corrected, root development is restricted, reducing crop yields, particularly under drought conditions in rainfed systems. Liming is essential not only for improving yields but also for enhancing crop resilience to water deficits, especially when amendments are incorporated into deeper soil layers. However, conventional methods often underestimate limestone requirements when aiming for subsoil pH correction. Given the relationship between soil pH and Ca and Mg-saturation in the cation exchange capacity (CEC) at pH 7.0, this study aimed to determine the optimal Ca and Mg proportions in the CEC required to achieve 95 % relative yield (RY) of annual crops, and to propose a method for estimating limestone requirements. Seven field experiments were conducted over four years, with varying limestone rates incorporated to 0–0.40 m. Soil pH showed a significant negative correlation with potential acidity and positive correlations with Ca and Mg-saturation at both 0–0.20 and 0.20–0.40 m depths. Critical Ca levels for 95 % RY were 4.1 cmolc dm⁻³ (0–0.20 m) and 1.9 cmolc dm⁻³ (0.20–0.40 m), while critical Mg levels were 2.0 and 1.0 cmolc dm⁻³ , respectively. Grain yield data indicated that 95 % RY was achieved at approximately 60 % Ca and 29 % Mg-saturation in the 0–0.20 m layer, and 39 % Ca and 20 % Mg in the 0.20–0.40 m layer. A target of 60 % Ca-saturation was adopted for a new liming rate calculation method.