Vol. 79 No: 3

Title:
N uptake, soil retention and loss of soil-applied ¹⁵NH₄¹⁵NO₃ in young Fuji/M.26 apple trees with different N status

Authors:
S DONG, L CHENG, C.F. SCAGEL and L.H. FUCHIGAMI

pp: 395-399

Abstract:
Nitrogen (N) uptake, soil retention and loss of soil-applied N were studied in young apple trees with different N backgrounds. Bench-graft potted Fuji/M.26 (Malus domestica Borkh) trees were fertigated with 5, 10 or 20 mM N twice a week from June to August, and the trees were removed from soil and bare-root stored in a 2°C cold room in December of the first season. In April of the second season, the trees were washed and replanted in containers with a N-free medium (perlite:vermiculite=l:l v), and received 500 ml Hoagland`s nutrient solution without N weekly through the experiment. The trees received ¹⁵NH₄¹⁵NO₃ at 1g per plant or no N on June 21. Four trees from each treatment were harvested at one, two and four weeks after ¹⁵N application, and ¹⁵N and total N in plant tissues and soil were analysed. N fertigation rates during the first growing season increased tree growth and N reserve levels, and N content in trees in the second year. New shoot and leaf growth in the following season was positively related to reserve N. ¹⁵N uptake increased during the four weeks after ¹⁵N application while soil ¹⁵N retention decreased. There was no significant difference in the total ¹⁵N uptake per tree. However, trees with the lowest N contents at the end of the first growing season had the highest rate of ¹⁵N uptake per unit root dry weight. Four weeks after application of ¹⁵N, tree uptake of N accounted for about 60&percent; of applied ¹⁵N, while about 20&percent; of the N still remained in the soil, and another 20&percent; of the N was lost. Our results suggested that trees with lower N status are more efficient in N uptake from soil.

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