The phosphorus nutrition of the apple tree. III. Influence of phosphate timing treatments on the performance of Jonathan/MM.104 apple trees in two years

Bench grafted JonathanlMM104 apple trees were grown in perlite culture in a glasshouse for up to 2 years and the effects of adding � phosphate (PO or P50 ppm nutrient solutions) in spring, summer, autumn, or during the second growing season were determined. Phosphate timing treatments produced marked differences in tree performance and P uptake. Thus, spring P significantly increased the growth of tree tops, the top/root ratio, P uptake and flowering in the second year. Summer P increased the growth of tree tops, the top/root ratio and P uptake, while autumn P increased P uptake but not tree growth in the first year. Strong carryover effects were note for all first year P treatments on the growth and P content of the trees in the second year consistent with the mobilization of P reserves. Significant interaction effects between treatments were found and P uptake in a given period was influenced by the P treatment given in the previous period. Thus, P uptake and the tree growth response were greater in P stressed trees than in high P trees. All times of application of P were effective in increasing the P status of tree parts including leaves and fruit. Tree P content at the end of the second year was dependent upon both residual and current year P treatments. These findings are briefly discussed in relation to earlier published work on the P nutrition of apple trees and also in relation to their significance to apple growers.