© 2001 Heron Publishing—Victoria, Canada
Remobilization and uptake of N by newly planted apple (Malus domestica) trees in response to irrigation method and timing of N application
D. Neilsen (1), P. Millard (2), L. C. Herbert (1), G. H. Neilsen (1), E. J. Hogue (1), P. Parchomchuk (1) and B. J. Zebarth (3)
1. Pacific Agri-Food Research Centre, Summerland, BC V0H 1Z0, Canada / 2. Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen, AB9 2JQ, U.K. / 3. Potato Research Centre, Box 20280 Fredericton, NB E3B 4Z7, Canada / Received April 13, 2000
Summary
Environmentally sound management of N in apple orchards requires that N supply meets demand. In 1997, newly planted apple
trees (Malus domestica Borkh. var. Golden Delicious on M.9 rootstock) received daily applications of N for six weeks as Ca(15NO3)2 through a drip irrigation system at a concentration of 112 mg l–1 at 2–8, 5–11 or 8–14 weeks after planting. Irrigation water was applied either to meet estimated evaporative demand or at
a fixed rate. In 1997, trees were harvested at 5, 8, 11 and 14 weeks after planting; and in 1998 at 3 weeks after full bloom.
The amount of fertilizer N recovered was similar in trees in both irrigation treatments, but efficiency of fertilizer use
was greater for trees receiving demand-controlled irrigation than fixed-rate irrigation. This was attributed to lower N inputs,
greater retention time in the root zone and less N leaching in the demand-controlled irrigation treatments compared with fixed-rate
irrigation treatments. Less fertilizer N was recovered by trees receiving an early application of N than a later application
of N and this was related to the timing of N supply with respect to tree demand. Demand for root-supplied N was low until
11 weeks after planting, because early shoot and root growth was supported by N remobilized from woody tissue, which involved
55% of the total tree N content at planting. Rapid development of roots > 1 mm in diameter occurred between 11 and 14 weeks
after planting, after remobilization ended, and was greater for trees receiving an early application of N than for trees receiving
a later application of N. Late-season tree N demand was supplied by native soil N, and uptake and background soil solution
N concentrations were higher for trees receiving demand-supplied irrigation compared with fixed-rate irrigation. Total annual
N uptake by roots was unaffected by treatments and averaged 6–8 g tree–1. Nitrogen applications in 1997 affected growth and N partitioning in 1998. Trees receiving early applications of N had more
flowers, spur leaves and bourse shoots than trees receiving later applications of N. Consequently, more N was remobilized
into fruits in trees receiving early applications of N compared with fruits in trees receiving later applications of N.
Demand for N in the young apple trees was low. Early season demand was met by remobilization from woody tissues and the timing
of demand for root-supplied N probably depends on whether flowering occurs. Method of N delivery affected the efficiency of
N use. We conclude that N demand can be met at soil solution N concentrations of around 20 mg l–1.
Keywords:
demand-controlled irrigation, fertilization, fertilizer-use efficiency, fixed-rate irrigation, nitrogen, orchard management.
