Phosphorus fixation studies with tomatoes on a krasnozem soil

Abstract

A series of glasshouse experiments was conducted with a krasnozem soil to determine the effect of previous applications of superphosphate on the rate at which the soil was able to fix further additions of phosphorus. Two soil samples were investigated, one a virgin soil, and the other a cultivated soil which had been fertilized with superphosphate. Fixation of currently applied phosphorus was measured by comparing plant data from treatments in which time of contact between soil and applied phosphorus varied from 0 to 16 weeks. Sixteen weeks contact between soil and fertilizer phosphorus prior to planting resulted in lower plant weight and less uptake of phosphorus on both soils but the effect was greater on the virgin soil. This showed that the rate of fixation was reduced by the phosphorus accumulation. The quantity of phosphorus extracted by 0.01 N sulphuric acid may be useful in detecting changes in phosphorus status, but is unreliable for assessing available phosphorus on this soil.