Excessive soil acidity is known to have potential negative impacts on crop production. The chemical and physical characteristics of a liming material determine its capacity to neutralize soil acidity. The material CaCO3 equivalent (CCE) and fineness effectiveness estimates are included in effective CCE (ECCE) assessments of a material’s liming value and to decide application rates. The objective of this study was to evaluate the effect of particle size on efficiency at increasing soil pH of commercial calcitic and dolomitic agricultural lime (aglime) compared with pure ground CaCO3 and a commercial calcitic pelleted lime. Both aglime sources were fractionated to pass US Standard Tyler Mesh screen sizes 4 but not 8, 8 but not 20, 20 but not 60, and 60 but not 100, and 100. A rate equivalent to 7.1 Mg CCE ha-1 of the materials was mixed with three Iowa acidic soils having contrasting texture and organic matter, and were incubated for 7, 21, 35, 70, 105, 140, 175, and 210 days at 25 à  à °C and 80% field moisture capacity. Initial soil pH values were 5.20 to 6.01. Materials efficiency at increasing pH relative to pure CaCO3 showed large differences among soils, materials, fineness fractions, and incubation times. Increasing fineness increased the efficiency of the aglime fractions following an exponential trend with decreasing increments. On average across soils and the longest incubation period, calcitic aglime fractions efficiency relative to CaCO3 were 29, 39, 60, 81, and 97% for mesh sizes 4, 8, 20, 60, and 100, respectively. Efficiencies for the dolomitic aglime were lower (10, 20, 43, 66, and 86%). For the last incubation period, the commercial calcitic, dolomitic, and pelleted aglime sources had average efficiencies across all soils of 60, 47, and 90%, respectively.

Abbreviations: aglime, agricultural limestone; ANOVA, analysis of variance; CCE, calcium carbonate equivalent; ECCE, effective calcium carbonate equivalent.