and Plant Nutrition Home
used by plants:
(when soil pH <7) and HPO42- (when soil
in energy transfer in plant cells
of nucleic acids, coenzymes, phospholipids, and phytic acid
seed development and root formation
foliage range for apple leaves:
0.08% may indicate P deficiency but in most cases, some other factor may
be limiting P availability to crop. It is usually pH limited (P most
available with soil pH between 6-7.0).
between 5 and 20 pounds of phosphorus per acre per year, or the
equivalent of 10-45 pounds of P2O5 per acre per
ppm (Olsen test should be used in our area)
10 ppm is considered low
40 ppm is considered to be excessive
tests are not usually a good indicator of phosphorus stats as related to
crop response. Availability
of this nutrient is largely controlled by soil pH.
As the pH of acid soils is increased or that of alkaline soils is
reduced toward neutrality (soil pH 6.0-7.0 is optimum), the levels of
soil P tend to increase even though no P fertilizer has been added. At soil pH levels below 6.0, P is generally in an unavailable
form because of reactions with soluble iron, aluminum, or manganese, or
their hydroxides. At pH
levels above 7.0, phosphorus fixation occurs thus making it unavailable
for plant uptake.
analysis provides the best means currently available for determining the
status of phosphorus in fruit trees (tree Fruit Nutrition). Extremely
high levels of P on the soil or in the leaves may be associated with
zinc deficiency. Soil tests
for P correlate well with cover crop and sod growth.
symptoms (rare in WA state):
leaves are affected first and may be small, bluish green on the
margins or main veins or undersides of leaves having purple
leaves drop early. Flowering
is reduced. Fruit quality
may be affected. Delayed maturity.
of fertilizer P may be advantageous in nurseries and replanted
problems/Interactions with other elements:
leaf P levels may indicate zinc or copper deficiencies.
When the P:Zn ratio is 150:1 or more, Zn deficiencies are
possible. Ratios of 50:1 or
lower indicate adequate supply, providing foliar sprays of Zn compounds
have not contaminated leaves. P:Cu ratios are less definitive.
It is estimated that ratios of 200:1 may indicate Cu
will enhance the absorption of molybdenum.
fertilization can increase P concentration in plants by increasing
root growth, by increasing the ability of roots to absorb and
translocate P, and by decreasing soil pH as a result of the absorption
of ammonium (NH4+) and thus increasing the
solubility of fertilizer P.
updated: 14 February, 2001