The effect of early superphosphate toxicity on the subsequent growth of wheat

Abstract

The effects of 19 days' treatment with three rates of superphosphate and four rates of ammonium nitrate application on the growth of wheat in a siliceous sand have been studied both during and after treatment. Severe necrosis of leaf tips developed after 7 days at high superphosphate and no ammonium nitrate. Plant tops with symptoms had high concentrations of phosphorus. Decreasing superphosphate or increasing ammonium nitrate gave lower phosphorus concentrations and fewer symptoms in plant tops. Ammonium nitrate depressed phosphorus concentrations by promoting top growth relative to root growth. Symptoms were ascribed to phosphorus toxicity. When plants with severe symptoms of phosphorus toxicity were transplanted to siliceous sand and watered with complete nutrient solution containing adequate phosphate, tillering was delayed and dry weights of tops, roots, and grains were depressed about 30%. Plants with symptoms of only moderate intensity recovered and grew as well as plants which initially had mild or no symptoms. The results suggest that the intensity of phosphorus toxicity reported to occur in cereal crops in the field is not likely to depress yields seriously.