EFFECTS OF NITROGEN, PHOSPHORUS, WATER AND PRE-PLANTING SOIL STERILISATION ON GROWTH AND YIELD OF QUEEN COX/M9 APPLE TREES

Phosphorus fertiliser applied either by broadcasting or as fertigation (irrigation + P fertiliser) increased the amount of bicarbonate-extractable P in the soil at 0–15 cm compared to soil not receiving supplementary P. Additionally, at 15–30 cm, fertigation increased the concentration of extractable P to a greater extent than at the shallower depth.

Trees receiving P-fertigation contained the highest concentrations of P in their leaves, but those receiving irrigation without P usually had greater concentrations than those receiving broadcast applications of P without irrigation. Irrigation reduced the concentration of N in the leaves but N fertiliser increased it.

Irrigation consistently increased new shoot growth compared to unirrigated treatments. Nitrogen fertiliser and pre-planting soil sterilisation also increased shoot growth compared to untreated controls, but the effects were smaller than those produced by irrigation. Phosphorus fertiliser, either with or without irrigation, did not influence growth. The fruit yield was increased by irrigation and soil sterilisation. Nitrogen fertiliser increased mean fruit size irrespective of application method. Irrigation increased growth more consistently than soil sterilisation and has potential, as an alternative method to overcome specific apple replant syndrome.

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