SOILS AND FERTILIZERS:
FERTILIZERS |
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MG
Manual Reference Ch. 2, pp. 22 - 23 |
[Fertilizers:
fertilizers | analysis |
types | organic
| applying |
application |
improving |
compost ]
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There are 18 elements essential to plant growth.
Nitrogen, phosphorous, potassium, calcium, magnesium, and sulfur
are considered fertilizer macronutrients because plants require
them in the largest quantity for maximum growth.Nitrogen,
phosphprous and potassium are the primary nutrients, which are
most likely to be present in inadequate amounts. Calcium,
magnesium, and sulfur are secondary macronutrients and usually are
either present in sufficient quantities or are added
coincidentally with other materials (e.g., fungicides, irrigation
water). The other 12 nutrients, called micronutrients, are just as
important but necessary in smaller amounts. If plants lack any of
these elements, they exhibit signs of nutrient deficiency. Some of
these symptoms are given in the discussion of
nutrients in Chapter 1
on Botany. |
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The analysis prouded on a fertilizer package refers to
the amount of an element present in a formulation based on
percentage of weight. All fertilizers are labeled with three
numbers, giving the percentage by weight of nitrogen (N),
phosphate (P2O5), and potash (K2O)
respectively. Often, to simplify matters, these numbers are said
to represent nitrogen, phosphorus, and potassium, or N-P-K. We
should remember that it is not N-P-K, but N, P2O5,
and K2O. Moat fertilizerscontain no P2O5,
and K2O, but phosphorus and potassium are expressed as
the amount of fertilizer would contain if they were in P2O5
equivalent, and K2O form equivalent. (These forms of
expression are leftovers from the early days of chemistry, when
all elements were expressed as oxides.) For example, if we have a
100 pound bag of fertilizer labeled 10-10-10, it contains 10
pounds of N, 10 pounds of P2O5, and 10
pounds of K2O. To convert the P2O5
content to actual phosphorous content, multiply the given weight
by 0.43. To convert K2O content to potassium content,
multiply the given weight by 0.83. The rest of the fertilizer's
weight is filler. |
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Filler is important so that we can evenly spread the
fertilizer and avoid burning plants with too much fertilizer.
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For many years, there has been a model label law which
some states have adopted for the classification of fertilizers.
The law also establishes minimum levels of nutrients allowable and
provides specific labeling requirements. To date, model label
legislation has not met with total acceptance, so there are still
differences from state to state as to what constitutes a
fertilizer and the type of information on labels. Even so, the
information contained on fertilizer labels has been well
standardized, and the consumer is protected by state laws
requiring manufacturers to guarantee the claimed nutrients. |
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The law requires that the manufacturer guarantees
accuracy of what is claimed on the label. In some cases, a
fertilizer will contain secondary nutrients or micronutrients not
listed on the label because the manufacturer does not want to
guarantee their exact amounts. The gardener/consumer is assured
that nutrients listed on the label are actually contained in the
fertilizer. On fertilizer labels, the initials W.I.N. and W.S.N.
stand for Water Insoluble Nitrogen and Water Soluble Nitrogen,
respectively. The water soluble nitrogen (W.S.N.) dissolves
readily and is usually in very simple form, such as ammoniacal
nitrogen (ammonia) or nitrate nitrogen. Nitrogen which will not
dissolve readily may exist in other forms in the fertilizer. These
are usually organic forms of nitrogen (with the exception of urea)
that must be broken down into simpler forms before it can be used
by plants. |
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Water insoluble nitrogen (W.I.N.) is referred to as a
slow-release nitrogen source and delivers nitrogen at different
rates according to the amount and kind of material in its
composition. |
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The best fertilizer to use depends on many factors,
such as the nutrients needed, soil structure, soil chemistry, and
method of applying the fertilizer. |
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