Agriculture Reference
In-Depth Information
and accurately labeled. Treat testimonials in advertisements with a huge
grain of salt. If a material is intended to be used as a source of plant nutri-
ents and no fertilizer analysis is printed on the label, there is usually a very
good reason why it is missing.
There are, however, some good commercial organic fertilizers, including
some naturally occurring materials, that do not come with fertilizer analyses.
These products include such things as feather meal, greensand, and soybean
many common organic fertilizers. Like conventional fertilizer labels, phos-
phorus values are given as P O and potassium as K O equivalents.
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Calculating Application Rates
For an example, say that a foliar analysis of your young apple trees showed
low levels of nitrogen and the laboratory recommended applying 60 pounds
of nitrogen per acre (fruit crops often need about 60 to 90 pounds of nitro-
gen per acre [68 to 103 kg/ha] per year). We will further assume that this is
a newly established orchard and that we do not yet have a nitrogen-fixing
alley crop in place, nor much decomposing organic matter in the soil. All ni-
trogen must come from the applied fertilizer.
Because the need for nitrogen is acute and our soil's organic matter is
not yet releasing much nitrogen, we will use a fairly rapid-release fertilizer
in the form of blood meal. Blood meal contains about 12 percent nitrogen.
If you were to buy a commercial blood meal fertilizer, it might have a label
something like 12-2-0.6, indicating 12 percent N, 2 percent P O , and 0.6 per-
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cent K O.
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Amount of fertilizer per acre.
To calculate how much fertilizer to apply, di-
vide the amount of nitrogen needed by the percentage of nitrogen in the fer-
tilizer. The same procedure is used to calculate the amount of phosphorus,
potassium, or other nutrient to add. In this case:
