Influence of Source and Particle Size on Agricultural Limestone Efficiency at Increasing Soil pH.

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 commercially available 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 1, 3, 5, 10, 15, 20, 25, and 30 wk at 25 C and 70% field moisture capacity. Initial soil pH values were 5.20 to 6.01. Soil pH for all treatments reached a plateau near week 25. An efficiency index for increasing pH relative to increases with CaCO₃ showed large differences among soils, materials, aglime 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 two longest incubation periods, calcitic aglime fractions efficiency relative to CaCO₃ were 28, 39, 60, 80, and 97% for mesh sizes 4, 8, 20, 60, and 100, respectively. Efficiencies for the dolomitic aglime were lower but differences decreased with increasing fineness (35, 53, 71, 80, and 89% lower). For the last two incubation periods, the non-fractionated calcitic, dolomitic, and pelleted aglime sources had average efficiencies of 59, 52, and 88%, respectively.