INFLUENCE OF SOURCE AND PARTICLE SIZE ON AGRICULTURAL LIMESTONE EFFICIENCY AT INCREASING SOIL pH

INTRODUCTION 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 calcium carbonate (CaCO3) equivalent (CCE) and estimates of particle size impact on the efficiency at increase soil pH are considered when assessing a material’s liming value. The reaction of limestone particles within the soil depends largely on the soil pH and the material surface area in contact with the soil. Particle size then influences the speed of reaction, with finer materials allowing for more particles and surface area to react in a given volume of soil, and may also influence the maximum pH reached (Meyer and Volk, 1952; Motto and Melsted, 1960). A typical sample of aglime includes multiple particle sizes in varying proportions. Pelleted limestone is a particular liming product because finely ground aglime is granulated to facilitate the handling and application. It is generally assumed that the granules disintegrate effectively after application to most soil or after rainfall. An effective liming material has the potential to raise the soil pH to a desired level. An efficient liming material has the potential to raise the soil pH to a desired value with the smallest amount of material applied possible. Cost and availability must be taken into account when deciding to apply a liming material. Both CaCO3 and magnesium carbonate (MaCO3) in aglime increase soils pH, as other materials do. The Soil Science Society of America defines dolomitic limestone as a natural liming material composed mainly of carbonates of Mg and Ca in approximately equal. In production agriculture and limestone trade there is no widely accepted definition, however, an aglime containing more than 70% CaCO3 is usually referred to as calcitic and that containing 10% or more MgCO3 concentration is considered dolomitic. While MgCO3 has a higher acid neutralizing potential than CaCO3 (mainly due to a lower molecular weight), the reaction rate of dolomitic limestone is known to be slower (Lindsay, 1979; Rippy et al, 2007). Recent field experiments in Iowa also showed that the time to reach a certain pH value was longer for dolomitic lime and that sometimes the maximum pH reached also was lower (Pagani and Mallarino, 2012). The objective of this study was to evaluate the effect of particle size on efficiency of commercially available calcitic aglime, dolomitic aglime, and calcitic pelleted lime at increasing soil pH in various Iowa soils under controlled conditions.