Agriculture Reference
In-Depth Information
% of leaf-absorbed N from autumn application of foliar urea to ap-
ple trees is recovered in permanent tissues during dormancy and is evenly dis-
tributed among root and stem tissues of the stock and scion (Hill-Cottingham
and Lloyd-Jones,
About
) found that post-harvest foliar
application of urea to 'Comice' pear increased the concentration of N in the
following winter and spring in the bark and wood of one-year-old shoots and
in flower buds and blossoms.
Foliar sprays of urea are widely used as a supplementary source of nitrogen.
Spraysof
). Sanchez
et al.
(
lwatermaybeappliedbeforeorafterblossom
or two to three times during the growing season beginning after flowering.
Post-harvest spray with
.
-
.
kgureaper
kg urea per
l may be applied prior to leaf fall.
Phosphorus nutrition
The net uptake of phosphorus by apple trees is much lower than that of nitro-
gen, potassium and calcium (Table
), and the concentration of P necessary
in apple and pear leaves to avoid deficiency symptoms is much lower than that
of the other major nutrient elements (Table
.
). Notwithstanding the key role
of P in the DNA and RNA macromolecules, in energy transfer involving ATP
and in many enzymic processes, phosphorus deficiency is seldom observed in
the orchard.
Concentrations of P in the soil solution are usually very much lower than
those of N, K, Ca and Mg (Robson and Pitman,
.
). These elements are
presentatmedianvaluesof
,
,
and
µ
Mrespectivelywhereas
the corresponding value for P is
M. More than for any other element,
the uptake of P has to be a metabolically driven process. Its concentration in
xylem sap is around
µ
times higher than that in the soil solution (Bieleski and
Ferguson,
) and its concentration in plant cells is up to
times as high.
) found that in both young and mature apple trees P influxin-
creased approximately linearly with concentration in the external solution up
to about
Bhat (
mmol m
−
uptake is negligible. Uptake rates are much higher in summer than in spring
(Asamoah,
mmol m
−
. At external concentrations below
.
-
.
) found that
P supplied in early spring was
not detectable in leaves for at least a month and ringing experiments showed it
to be translocated in the phloem. The phosphorus used in early leaf and shoot
growth appears to come from reserves, mainly those in bark. Bark P content
falls steeply in April, simultaneously with a fall in N, whereas branch wood
concentration shows a slower decline and the concentration in trunk wood
is fairly constant (Mason and Whitfield,
). Harley
et al.
(
). The concentration of P in the
bark, roots, and the previous year's extension wood rises sharply in October
when P is exported from the leaves.
