The reaction rate and residual value in southern New South Wales of 12 commercial liming materials from around Australia

Context Farmers and consultants are faced with selecting from amongst competing liming materials. Aim We sought to establish guidelines for the efficient use of competing liming materials. Method The effectiveness of 12 commercial liming materials from around Australia in increasing soil pH, their rate of movement below the depth of incorporation and their residual value to grain yield were measured in our field study. Key results Chemical composition (equivalent CaCO3 content) was a major determinant of effectiveness over the longer term. There appeared to be no value to grain yield in the provision of additional Mg above what was already in the soil at this site. Finer commercial products were more effective in the short term and no less effective in the longer term, indicating that fineness also remains a major determinant of effectiveness. The effect of the source of the liming product was a minor determinant of effectiveness. As previously found, there was a tardiness in the reaction rate of dolomites and a slight advantage in the reaction rate of softer limestones but as with fineness, the data for different sources tended to converge over 6-7 years. Conclusion All liming materials provided a benefit to grain yield over the 7 years and that benefit was proportional to the material's chemical purity and fineness. Implication Growers and advisers can select the best value for cost amongst the commercially available products at a given geographical location. The quantitative assessment of chemical composition and particle size remains the best means of assessment over both the short and longer terms.