title: Remobilization and uptake of N by newly planted apple (Malus domestica) trees in response to irrigation method and timing of N application.
abstract: 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).
authors.affiliation: Pacific Agri-Food Research Centre, Summerland, BC V0H 1Z0, Canada.
authors.forename: D
authors.initials: D
authors.lastname: Neilsen
authors.forename: P
authors.initials: P
authors.lastname: Millard
authors.forename: L C
authors.initials: LC
authors.lastname: Herbert
authors.forename: G H
authors.initials: GH
authors.lastname: Neilsen
authors.forename: E J
authors.initials: EJ
authors.lastname: Hogue
authors.forename: P
authors.initials: P
authors.lastname: Parchomchuk
authors.forename: B J
authors.initials: BJ
authors.lastname: Zebarth
mesh_terms: D000383:Agriculture; D027845:Malus / Q000254:growth & development / Q000502:physiology*; D009584:Nitrogen / Q000502:physiology; D012987:Soil; D014197:Trees / Q000254:growth & development / Q000502:physiology*; D014867:Water
chemical_list: D012987:Soil; D014867:Water; D009584:Nitrogen