Response of apple trees to soil applications of phosphorus, nitrogen and potassium

Abstract

An experiment was conducted at Manjimup Research Station in Western Australia from 1973 to 1982 to determine the optimum rates of fertilizer applications for apple trees (Granny Smith/MM.104 and Hi Early Red Delicious/MM.104) growing in a P-deficient soil (about 6 mg/g bicarbonate-extractable P). The trees were planted at 6.1 multiply 6.1 m spacings. Superphosphate at 5 or 8 kg/tree consistently increased fruit set, but the increase varied from year to year from 8 to 91%. Weight of prunings increased by 24-29% and tree height multiply width by 11-16%. When results were averaged over both cultivars, weight of fruits harvested from 1973 to 1982 was increased from 853 to 1226 kg/tree by superphosphate application at 5 kg/tree. Ammonium nitrate applied at up to 4 kg/tree gave small non-significant increases in growth and no increase in weight of fruits harvested for Granny Smith, but the weight of the Red Delicious crop rose by 11%. No response to potassium chloride at 1 kg/tree was found. P fertilizer application increased P concentration in the first fully mature leaves of Granny Smith trees from approximately 0.14% to 0.17-0.19% and in Red Delicious leaves from 0.17 to 0.20-0.21%. N fertilizer application increased N concentration in Granny Smith leaves from approximately 2.3 to 2.5%. Lack of P was the main limiting factor on growth and cropping and it is suggested that the importance of P nutrition in Western Australian apple orchards has been underestimated.