Annual bloom-time phosphorus fertigation affects soil phosphorus, apple tree phosphorus nutrition, yield, and fruit quality.

摘要

A randomized, complete block, split-plot experimental design with 6 replicates was established and maintained annually for the 1st 5 fruiting seasons (1999-2003) in a high-density apple orchard on M.9 rootstock planted in April 1998. Main plot treatments involved 8 different nutrient regimes, each containing 3 tree subplots of 5 different cultivars (Ambrosia, Cameo, Fuji, Gala, Silken). Effects of a +P treatment, involving annual fertigation at bloom time of 20 g P/tree as ammonium polyphosphate (10N-15P-0K) were compared to a -P treatment. Both treatments also received N, K and B through fertigation. Drip fertigation of P increased 2M KCl-extractable P to 0.4 m depth within 0.5 m distance of the drippers. Leaf and fruit P concn. were consistently increased by the +P treatment with few differences among cultivars. P-fertigated trees also had a 20% increase in cumulative yield overall during the 1st 5 fruiting seasons. Standard fruit quality measurements, including fruit size, soluble solids concn., titratable acidity and red coloration were unaffected by P application. However, reductions in incidence of watercore at harvest, increased resistance to browning and elevated antioxidant content of harvested fruits measured in some yr imply a role for P in apple membrane stability. Cumulative results indicate that applications of 20 g P as ammonium polyphosphate annually at bloom would be advantageous for apples receiving adequate fertigated applications of N, K and B. Best apple performance was associated with leaf P concn. of >2.2 mg g-1 dry wt. and fruit P concn. between 100 and 120 mg kg-1 dry wt.