Overview
Field evidence demonstrating an exponential increase in lime effectiveness as particle size decreases
This peer-reviewed study, published in the Australian Journal of Agricultural Research, investigated how particle size influences the effectiveness of calcitic limestone (calcium carbonate, CaCO₃) in amending acidic soils. The research was conducted by NSW Agriculture at the Agricultural Research Institute in Wagga Wagga under field conditions over a three-year period.
Calcitic limestone with a purity of approximately 98% was separated into six distinct particle size fractions, with mean diameters ranging from 3.0 mm down to 5 microns. These materials were applied at rates of 2.5, 5.0, and 10.0 tonnes per hectare and incorporated into the soil. Changes in soil pH, exchangeable calcium, and crop response were monitored at multiple intervals up to 36 months after application.
The study found no minimum particle size at which lime reached maximum effectiveness. Instead, lime effectiveness increased continuously as particle size decreased across the entire range tested. The relationship between particle size and soil pH response was exponential, with progressively finer particles producing larger and faster increases in soil pH and exchangeable calcium.
Most of the soil pH response occurred within the first six months following application, indicating rapid reactivity of fine particles. Coarser particles continued to react slowly over time but never achieved the same level of effectiveness as finer lime.
The researchers concluded that, subject to cost and handling considerations, fine and ultra-fine limestone should be preferred where rapid and efficient soil acidity correction is required.
👉 Download the full reasearch PDF below to explore the trial data, charts, and detailed results.