Saturday, 15 July 2006

Effective P Fertigation Increases Yield and Quality of Fruit in High Density Apple.

Gerald Neilsen, Denise Neilsen, and Peter Toivonen. Pacific Agri-Food Research Centre, Highway 97, Summerland, BC V0H 1Z0, Canada

Much historical research from P-fertilization experiments indicated that high value, perennial tree-fruit crops, such as apple (Malus domestica Borkh.) are unlikely to meaningfully respond to soil P applications. This was attributed to modest unit area requirements for this nutrient in traditional, low density orchards. This belief has persisted despite the widespread advent of high density apple orchards on dwarfing rootstocks which alter nutrient demand as a result of earlier and greater unit area fruit yield. At the same time, precision nutrient and water management techniques, including fertigation, have increased the flexibility in managing orchard nutrition programs because of the potential for more closely synchronizing nutrient application with plant demand. Phosphorus mobility is much greater when fertigated than surface broadcast, increasing the potential to apply this nutrient rapidly when required and transport it to the root. A fertigation experiment was established within the major fruit growing region in Pacific North Western North America in order to assess the effect of early season P-fertigation on soil and plant P availability and yield and quality of apple fruit. Five new apple cultivars including Gala, Ambrosia, Cameo, Fuji and Silken on dwarfing M.9 rootstock were planted in 1998, spaced at 1 meter within rows separated by 3 meters, on a Skaha loamy sand soil which is extensively planted to orchards and vineyards in southern British Columbia. Commencing in 1998 and for the first 5 growing seasons, the block was maintained in a randomized, split plot experimental design involving 8 fertigation main plot treatments, replicated 6 times, each rep comprising 3 tree plots of each cultivar. Irrigation, as required in the region was applied daily, via 2 X 4 L /hour drip emitters/ tree, according to evaporative demand measured by an atmometer, modified by crop coefficients. Treatments included: high N (target soil solution concentration 168 ppm); low N (target soil solution concentration 28ppm), each applied as calcium nitrate at time A (0-4 weeks post bloom(pb), time B (4-8 weeks pb) and time C (8-12 weeks pb) and annual application of 20 g P per tree as ammonium polyphosphate soon after bloom with high N at time A. Over the first 5 growing seasons maintenance of a high N fertilizer regime increased leaf N concentration (<10%) and fruit N concentration (10-20%) but consistently decreased fruit firmness and to a lesser extent per cent red color. Changing the timing of N-application altered leaf and fruit N concentration but had few consistent effects on fruit quality or yield. The P treatment consistently increased leaf and fruit P concentration compared to trees receiving high N only during time A. The P treatment had highest cumulative yield of all treatments. Fruit quality was also improved as indicated by reduced incidence of water core disorder and improved fruit membrane stability as well as reduced susceptibility to browning when cut. Fertigation of a single P application thus improved soil P mobility without serious reductions in soil pH, thereby increasing P availability to apple trees.

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