Response of wheat to applied superphosphate; the relationship between yield increase and 'available' phosphate in the soil

Abstract

Seventy-one trials were sown to wheat during the years 1964-66, and of these 54 were successfully harvested. They were of 5 x 2 factorial design with five levels of superphosphate and two levels of nitrogen ; there were three replications. Superphosphate increased grain yield in two thirds and nitrogen in about one sixth of the trials. The yield of grain and the increase in grain yield resulting from fertilizer application were markedly affected by seasonal conditions. Soil samples were taken from each site and analysed for pH, and for 'available' phosphate by ten extractant methods. The yield increase was correlated with superphosphate applied and 'available' phosphate in the model : -Y = bo+b1S+b2vS+b3P+b4P2+b5vSP and the highest coefficient of determination was 31.4 per cent. When pH and average annual rainfall were put into the equation -Y = bo+b1pH+b2RA+b3S+b4vS+b5P+b6P2+b7vSP the highest coefficient of determination was 54.4 per cent.