Particle size determines the efficiency of calcitic limestone in amending acidic soil

Abstract

There is a commonly held view that limestone particles <0.25 mm are fully effective in amending acidic soils. However, this is not consistent with some available data. We assessed the importance of particle size in a field experiment using six particle size segregations covering a range of mean diameters from 3 mm to 0.005 mm. These products were applied at rates of 2.5, 5 and 10 t ha-1. Lime was incorporated in April 1986 and soil samples were collected 6, 12, 24 and 36 months later. The experiment was cropped to wheat in 1986, 1987 and 1989. Effectiveness was evaluated as the capacity of the particle size segregation to increase soil pH, exchangeable calcium (Caex,) or grain yield of wheat. No minimum particle size for maximum effectiveness was identified. Throughout the range of particle sizes evaluated, progressively finer particles produced larger increases in pH and Caex. Wheat yield was related to soil pH. Changes in soil pH and Caex between 6 months and 3 years after lime application were small compared to the changes in the first 6 months. Fine lime products should be preferred in practice, subject to cost considerations and handling difficulties.