Nitrogen fertigation concentration and timing of application affect nitrogen nutrition, yield, firmness, and color of apples grown at high density.

摘要

A randomized complete block, split-plot experiment with 6 replicates was established and maintained for the first 6 fruiting seasons (1999-2004) in a high-density apple orchard on M.9 rootstock planted in Apr. 1998. Responses to 6 main-plot fertigation treatments, each containing 3 tree subplots of 5 different cultivars (Ambrosia, Cameo, Fuji, Gala and Silken) were assessed. Fertigation treatments were a factorial combination of 2 N rates and 3 N application timings. N was applied at low (28 mg N/l) or high (168 mg N/l) concn. daily at 0-4, 4-8, or 8-12 wk after full bloom (wafb). Under greater N inputs, all cultivars had increased midsummer leaf and harvested fruit N concn., decreased fruit firmness, and in heavy crop yr, decreased percent red colour. Annual yield of all cultivars was significantly increased by N rate in a single yr, but their cumulative yields were not different between treatments as a result of rate or timing. Altering the timing of N application within 12 wafb only affected leaf and fruit tissue N concn. Leaf N was higher after 4 wk of fertigation any time, although concn. declined over the growing season, reaching min. values around harvest. Fruit N was increased by fertigation 4-12 wafb. Yield, fruit firmness and colour were unaffected by fertigation timing. Critical fruit quality issues for Gala and Silken were small fruit size, for Ambrosia low fruit numbers, and for Cameo soft fruit. Fuji, which achieved high yield and leaf N concn. and firm fruit, had poor red colour regardless of N treatments.