Mineral nutrition of soybeans grown in the south Burnett region of south-eastern Queensland. I. Effect of phosphorus, potassium, calcium and sulfur on grain yield and plant composition

Abstract

Twenty-seven field experiments were carried out over the period 1973 to 1977 with soybeans Glycine max(L.) Merrill cv. Bragg on krasnozem, euchrozem and xanthozem soils in the South Burnett region of Queensland to study effects of phosphorus, potassium, calcium and sulfur on grain yield and plant nutrient composition. Grain yield responses (P< 0.01) were associated with increased seed number rather than heavier grain weights. These were recorded at approximately 30% of the 27 sites that received 20 or 40 kg P/ha and on 25% of 17 sites after an application of 50 kg K/ha. No yield gains were measured from applications of calcium and sulfur. Moisture stress from anthesis to maturity restricted grain production in all years but only in one were responses to applied nutrients seriously reduced. Indices for the attempted prediction of yield responses to applied elements were derived from the concentration of elements in leaves and whole tops collected at anthesis. Mean leaf phosphorus concentrations were 0.24% in control plots and 0.26% in fertilized treatments. No relation between leaf phosphorus and response to applied phosphorus could be established but leaf potassium concentration in control treatments averaged 0.66% at responsive sites and 1.64% at non-responsive sites.