The 17 essential elements
Form used by plants:
H2PO4- (when soil pH <7) and HPO42- (when soil pH>7)
Involved in energy transfer in plant cells
Component of nucleic acids, coenzymes, phospholipids, and phytic acid
Stimulates seed development and root formation
Ideal 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).
Range between 5 and 20 pounds of phosphorus per acre per year, or the equivalent of 10-45 pounds of P2O5 per acre per year
Ideal soil range:
10-20 ppm (Olsen test should be used in our area)
< 10 ppm is considered low
20-40 ppm high
> 40 ppm is considered to be excessive
Soil 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.
Leaf 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.
Mobility in plant:
Remobilized within plant
Deficiency symptoms (rare in WA state):
Older leaves are affected first and may be small, bluish green on the margins or main veins or undersides of leaves having purple pigmentation. Older leaves drop early. Flowering is reduced. Fruit quality may be affected. Delayed maturity.
Addition of fertilizer P may be advantageous in nurseries and replanted orchards.
Excess problems/Interactions with other elements:
High 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 deficiencies.
Phosphate will enhance the absorption of molybdenum.
Nitrogen 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.
July 13, 2004