© 1997 Heron Publishing—Victoria, Canada
Sources of N for leaf growth in a high-density apple (Malus domestica) orchard irrigated with ammonium nitrate solution
D. Neilsen (1), P. Millard (2), G. H. Neilsen (1) and E. J. Hogue (1)
1. Agriculture and Agri-Food Canada, Summerland, B.C. V0H 1ZO, Canada / 2. Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen AB9 2JQ, U.K. / Received September 16, 1996
Summary
Elstar apple trees (Malus domestica Borkh.) on M.9 rootstock received either 5 or 35 g N tree–1 year–1 during the first two growing seasons after planting, applied as Ca(NO3)2 on a daily basis for nine weeks through a drip irrigation system. During the third growing season (1994), all trees were
treated with 20 g N tree–1 year–1 as 15NH415NO3 with applications starting on April 22 and continuing for 10 weeks. Soil solution nitrate-N and ammonium-N were monitored
weekly with suction lysimeters located 30 cm beneath the drip emitters. Spur and shoot leaves were sampled intensively from
full bloom to the end of rapid shoot growth. During the period of nitrogen application, soil solution nitrate-N and ammonium-N
were relatively constant, at about 24 and 1.0 mg l–1 respectively. Growth of the spur leaves was completed by one week after full bloom (May 12), whereas biomass of the shoot
leaves increased until mid-June. Nitrogen for growth of the spur leaves was supplied mainly from remobilization, which was
dependent on previous N supply. Accumulation of fertilizer N in spur leaves was independent of previous N treatments and continued
until the end of the monitoring period (June 24), but contributed only 13% to total spur leaf N. Nitrogen for shoot leaf growth
was independent of previous N treatments and was initially supplied primarily by remobilization, but by the end of extension
growth, fertilizer N contributed 48% to total shoot leaf N. Linear increases in leaf N uptake throughout the period of rapid
shoot growth and the large contribution of fertilizer N to total shoot leaf N were attributed to the constant supply of N
available in the root zone through daily N fertilization.
Keywords:
biomass, fertilization, nitrogen, nitrogen remobilization, nutrient cycling, partitioning, root uptake, shoot leaf, spur leaf.
