Jd. Lea-cox et al., Springtime (15)Nitrogen uptake, partitioning, and leaching losses from young bearing Citrus trees of differing nitrogen status, J AM S HORT, 126(2), 2001, pp. 242-251
Citations number
31
Categorie Soggetti
Plant Sciences
Journal title
JOURNAL OF THE AMERICAN SOCIETY FOR HORTICULTURAL SCIENCE
(15)Nitrogen uptake, allocation, and leaching losses from soil were quantif
ied during spring, for 4-year-old bearing 'Redblush' grapefruit (Citrus x p
aradisi Macf,) trees on root stocks that impart contrasting growth rates. N
ine trees on either the fast-growing 'Volkamer' lemon (VL) (C. volkameriana
Ten & Pasq,) or nine on the slower-growing sour orange (SO) (C. aurantium
L.) rootstocks were established in drainage lysimeters filled with Candler
fine sand and fertilized with 30 split applications of N, totaling 76, 140,
or 336 g.year(-1) per tree. A single application of double-labeled ammoniu
m nitrate ((Np4N3)-Np-15-N-15, 20% enriched) was applied at each rate to re
plicate trees, in late April, Leaves, fibrous roots, soil, and leachates we
re intensively sampled from each treatment over the next 29 days, to determ
ine the fate of the (NH4NO3)-N-15-N-15 application. Newly developing spring
leaves and fruit formed dominant competitive sinks for N-15, accounting fo
r between 40% and 70% of the total N-15 taken up by the various treatments.
Large fruit loads intercepted up to 20% of this N-15, at the expense of sp
ring flush development, to the detriment of overall tree N status in low-N
frees. Nitrogen supply at less than the currently recommended yearly rate o
f 380 g/tree exceeded the requirements of 4-year-old grapefruit trees on SO
rootstock; however, larger trees an VL rootstock took up the majority of N
-15 from this rate over the 29-day period, Nitrogen-use efficiency declined
with increasing N rate, irrespective of rootstock, The residual amounts of
N-15 remaining in the soil profile under SO trees after this time represen
ted a significant N leaching potential from these sandy soils. Therefore, u
nder these conditions, present N recommendations appear adequate for rootst
ocks that impart relatively fast growth rates to Citrus trees, but seem exc
essive for trees on slower-growing rootstock species.