The growth of improved pastures on acid soils. 3. Response of lucerne to phosphate as affected by calcium and potassium sulfates and soil aluminium levels

Abstract

A glasshouse experiment was conducted to study the response of lucerne to phosphate at various concentrations of aluminium in the soil solution. Aluminium levels were varied by adding neutral salts to an acid infertile soil, typical of those on which unusually poor responses to superphosphate have been reported on the Southern Tablelands of New South Wales. The addition of monocalcium phosphate reduced aluminium concentration in the soil solution and increased plant growth four-fold. The neutral salts, calcium sulfate and potassium sulfate, in the presence of calcium phosphate, increased aluminium concentrations in the soil solution and reduced plant growth and response to phosphate. It is concluded that the calcium sulfate component of single superphosphate can decrease plant growth, and thus the response to phosphate, by increasing the concentration of aluminium in the soil solution on these very acid soils..