and Plant Nutrition Home
used by plants:
building block for all plant parts – leaves, shoots, roots, fruit
acid synthesis and protein formation.
in chlorophyll, nucleic acids, and enzymes
Ideal foliage range for apple leaves:
|Age of tree
||Leaf N (%)
Ideal fruit concentration:
Ideal soil range:
The nitrogen-supplying power of the soil
is largely dependent upon soil texture and organic matter.
Mineralization rates will increase with an increase in organic matter
content (also C:N ratios, temperature and moisture driven). This will
supply the trees with some of the nitrogen they require.
Mobility: when in the nitrate (NO3-)
form, it is very mobile and can easily be leached from soils. The
ammonium (NH4+) form is not very mobile except in soils with
very low CEC (cation-exchange
capacity) and low organic matter.
Influence on soil pH:
uptake of nitrate or ammonium creates increased and decreased root
3NO3- ----> 3
NH2 + 2OH- (increases soil
3R-NH2 + 4H+ (decreases soil
growth and performance are the best indicators for nitrogen management
in orchards. To date, soil tests have not been useful in determining
tree needs. Additionally, leaf samples may be useful.
In general, leaf nitrogen levels are higher in samples from trees
carrying heavy crops. Biennial bearing trees in their off year or trees
with a light crop typically have lower nitrogen levels. Table 2 shows
leaf nitrogen standards for apple.
Mobility in plant:
of nitrogen fertilizer:
trees respond to any form of nitrogen fertilizer. Certain
considerations, however, should be addressed. For instance, ammonium and ammonium-forming fertilizers like
ammonium sulfate, urea, and ammonium nitrate will decrease soil pH over
time and are not recommended for soils with pH below 6.5. Nitrogen when applied as urea may be lost from the soil via
ammonia volatilization when this material is applied to the surface of
warm, moist, alkaline soils. Leaching
of nitrates is another manner by which nitrogen is lost from the system.
This is especially true with coarse-textured soils that are
sprays may be effective in increasing fruit set but are not sufficient
to supply apple trees with the entire N they require.
Nitrate sprays are not recommended for apple trees because it is
often associated with increased corking.
may also be applied to orchard soils with the irrigation water.
It is therefore recommended that the irrigation water be tested
periodically and credited against tree fertilizer requirements.
N is remobilized within the tree, older leaves will show deficiency
symptoms first. Leaves will
be small and uniformly light green or yellowish (see middle photo
above). Tips and margins
may show necrosis. Bark is
yellowish orange or will have a reddish tinge.
Shoots/spurs will be short, thin and spindly. Fruit set may be reduced.
Current season's growth is <4".
Fruit color however, is enhanced.
shoot growth; large, succulent, dark green leaves; profuse flowering
(see photo above); poor color development; prolonged growth into fall
and higher susceptibility of winter injury and diseases such as
Interactions with other elements:
- Heavy N fertilization intensifies copper
and zinc deficiencies.
updated: 14 February, 2001