Comparative soil phosphorus requirements of four field crops

Abstract

A range of soil phosphorus levels was established at one site on a euchrozem near Kingaroy in south-east Queensland, by dispersing rates of triple superphosphate (0-480 kg P/ha) through the 0-100 mm layer. Following two cover crops to allow equilibrium between fertiliser and soil, successive crops of barley, soybean, sorghum and peanut were grown. For each plot and each crop, Mitscherlich equations were fitted to relative seed yield versus extractable soil phosphorus levels determined on soil samples taken prior to planting. Bicarbonate extractable P levels corresponding to 90% maximum seed yield for sorghum, barley, soybean and peanut were 34, 29, 18 and 10 mg/kg respectively. Relative seed yields at the low bicarbonate extractable P levels (6-8 mg/kg) of the nil applied phosphorus plots decreased in the order: peanut > > soybean > sorghum > barley. In terms of increasing ability to utilise banded phosphorus fertiliser, the crops ranked: peanut < soybean < sorghum <barley.