SOLUBLE ALUMINUM STUDIES

Abstract

Various amounts of different phosphate compounds were added to a very acid soil, and the effect on plant growth and on the pH and the Al, P, and Ca concentration of the displaced soil solution was studied. Addition of large amts. of superphosphate reduced the concentration of Al in the displaced soil solution by approximately 1/2; but the fact that 8-10 p.p.m. Al still remained in solution and that good growth of barley and alfalfa resulted was taken to indicate that the beneficial action of large phosphate additions to acid soils is partly due to the reaction of Al and phosphate within the plant and not entirely to the precipitation of Al in the soil solution. This conclusion is further substantiated by controlled culture solution studies; 2.5 p.p.m. of Al reduced the yield of Cos lettuce 23% in the presence of 50.0 p.p.m. PO4 in solution, whereas the yield was reduced by 71% in the presence of only 1.0 p.p.m. PO4. Moreover, the inorganic phosphate concentration of the exuded sap from the lettuce plants receiving Al was in some cases only 1/5-1/7as high as from plants which did not receive Al. Apparently, large phosphate additions to acid soils reduce the injurious action of Al not only by tending to precipitate it from solution, but also by supplying sufficient P to precipitate Al within the plant, as well as to meet the nutritional needs of the plant for P.