The Effect of Soil Reaction on the Availability of Phosphorus for Alfalfa in Some Eastern Ontario Soils

Abstract

The yields and phosphorus contents of alfalfa grown with and without phosphorus fertilizer in six soils previously limed to different pH levels in pots, and the amounts of phosphorus extracted with four chemical methods from soil samples taken prior to seeding and after harvest of the crop, were used to evaluate the effect of soil reaction on the availability of native and applied phosphorus for alfalfa.The greatest uptake of phosphorus by alfalfa occurred at a pH of about 7.5, the highest level employed in the experiment. In most instances, the phosphorus contents of the plants were highest at a pH of about 7.5, at which level the yields were either similar to or higher than those obtained at any lower pH.The results for phosphorus in most of the soils as measured with the Truog and sodium bicarbonate methods and for Bray adsorbed phosphorus in three of the soils showed that liming to or slightly above the neutral point increased the amounts of available soil phosphorus.