Effect of lime source, fineness and granulation on neutralisation of soil pH

Little information is available regarding the liming efficiency of various local lime sources and products currently available in South Africa. Recently, granulated micro-fine limes are being widely marketed as being superior to class A limes. Therefore, the aim of this study was to compare the effectiveness of various local, commercially available hydrated, calcitic and dolomitic lime sources (i.e., from different quarries) and forms (class A, micro-fine and granulated micro-fine) at increasing soil pH over time (365 days) under controlled conditions in two contrasting acid soils (sand and loam). Liming materials were applied adjusted for calcium carbonate equivalence (CCE) to achieve a target pHKCl of 5.5 and incubated at 85% field capacity. Micro-fine calcitic limes and hydrated limes increased pH the fastest (first 30–60 days), but the difference between these materials and class A limes attenuated over time. The difference in performance between class A limes was relatively minor (0.5 pH units), if applied based on CCE. Chemical purity (Ca%, CCE) was the main factor controlling liming effectiveness and particle fineness only related to the short-term reaction (4–7 days). Granulated limes showed the poorest performance in terms of pH correction attributed to poor solubility and spatial zonation of liming effects.