Studies on the nutrition of forage legumes

Summary Surface samples of six Ontario soils were selected to provide a range in pH, texture and carbonate content. Phosphorus was added to the soil samples at the rate of 200, and 2000 pounds. P₂O₅ per acre and the inorganic phosphates associated with aluminum (Al-P), iron (Fe-P) and calcium (Ca-P) were analysed 15, 30, and 335 days after treatment. Samples of the check soils were leached with the equivalent of 7 litres of soil-percolated water and then analysed for phosphate fractions. In 5 soils with added phosphorus the Al-P fraction increased at both rates of added phosphorus, Fe-P increased only at the higher rate of added phosphorus and Ca-P did not increase at either rate. In the sixth soil (69.9% CaCO₃ equivalent) Ca-P increased at both rates of added phosphorus, but proportionately less than the water-soluble phosphorus. These changes in phosphorus values existed relatively unchanged for 335 days after the addition of phosphorus. Leaching generally removed phosphorus from all phosphorus fraction. At or below pH 7.1 (soil paste) the Al-P decreased proportionately more than the Fe-P and Ca-P. Above pH 7.1 the Ca-P decreased proportionately more than the other two fractions upon leaching.Contribution from Dept. of Soil Science, O.A.C., Guelph, Canada. Part of thesis submitted by junior author to the Graduate School, University of Toronto, in partial fulfilment of the requirements for the M.S.A. degree.