fertilizers | analysis
| types | organic |
SOILS AND FERTILIZERS:
Ch. 2, pp. 27 - 31
Comparison of Fertilizers
- Fast acting.
- Some are acid-forming.
- Low cost.
- Greater burn potential.
- Solidifies in the bag when wet.
- Nitrogen leaches readily.
- Fewer applications.
- Low burn potential.
- Release rate varies depending on fertilizer
- Comparatively slow release rate.
- Unit cost is high.
- Availability is limited.
- Release rate governed by factors other than plant need
Manures or Sewage Sludge
- Low burn potential.
- Relatively slow release.
- Contain micronutrients.
- Conditions the soil.
- Salt could be a problem.
- Bulky, difficult to handle.
- Expensive per pound of actual nutrient.
- Weed seeds can be a problem.
- Heavy metals may be present in sewage sludge from large
cities or industrial areas.
The word organic, applied to fertilizers, simply means that the nutrients
contained in the product are derived solely from the remains or
by-products of a once-living organism. Urea is a synthetic organic
fertilizer, an organic substance manufactured from inorganic
materials (although urea is also, as the name implies, a
consititment of urine). Cottonseed meal, blood meal, bone meal,
hoof and horn meal, and all manures are examples of organic
fertilizers. When packaged as fertilizers, these products will
have the fertilizer ratios stated on the labels.
Some organic materials, particularly composted manures
and sludges, are sold as soil conditioners and do not have a
nutrient guarantee, although small amounts of nutrients are
present. Most are high in one of the three major nutrients and low
in the other two, although you may find some fortified with
nitrogen, phosphorus, or potash for a higher analysis. Many are
low in all three.
In general, organic fertilizers release nutrients over a
fairly long period; the potential drawback is that they may not
release enough of their principal nutrient at a time to give the
plant what it needs for best growth. Because organic fertilizers
depend on soil organisms to break them down to release
nutrients, most of them are effective only when soil is moist
and soil temperature is warm enough for the soil organisms to be
Cottonseed meal is a by-product of cotton
manufacturing. As a fertilizer, it is somewhat acidic in reaction.
Formulas vary slightly, but generally contain 7 percent nitrogen,
3 percent P2O5, and 2 percent K2O
. Cottonseed meal is readily available to plants in warm soils,
and there is little danger of burn. Cottonseed meal is frequently
used for fertilizing acid-loving plants such as azaleas,
camellias, and rhododendrons.
Blood meal is dried, powdered blood collected from
slaughter houses. It is a rich source of nitrogen - so rich, in
fact, that it may do harm if used in excess. The gardener must be
careful not to use more than the amount recommended on the label.
In addition to supplying nitrogen, blood meal supplies certain of
the essential trace elements, including iron.
Fish emulsion, a complete fertilizer, is a partially
decomposed blend of finely pulverized fish. No matter how little
is used, the odor is intense - but it dissipates within a day or
two. Fish emulsion is high in nitrogen and is a source of several
trace elements. In the late spring, when garden plants have
sprouted, an application of fish emulsion followed by a deep
watering will boost the plants early growth spurt. Contrary
to popular belief, too strong a solution of fish emulsion can burn
plants, particularly those in containers.
Manure is also a complete fertilizer, but low in the
amounts of nutrients it can supply. Manures vary in nutrient
content according to the animal source and what the animal has
been eating, but a fertilizer ratio of 1-1-1 is typical. Manures
are best used as soil conditioners instead of nutrient sources.
Commonly available manures include horse, cow, pig, chicken, and
sheep. The actual nutrient content varies widely: the highest
concentration of nutrients is found when manures are fresh. As it
is aged, leached, or composted, nutrient content is reduced.
However, the subsequent reduction in salts will reduce the chances
of burning plants. Fresh manure should not be used where it will
contact tender plant roots. Typical rates of manure applications
vary from a moderate 70 pounds per 1000 square feet to as much as
500 pounds per 1000 square feet.
Sewage sludge is a recycled product of municipal sewage
treatment plants. Two forms are commonly available: activated and
composted. Activated sludge has higher concentrations of nutrients
(approximately 6-3-0) than composted sludge, and is usually sold
in a dry, granular form for use as a general purpose,
long-lasting, non-burning fertilizer. Composted sludge is used
primarily as a soil amendment and has a lower nutrient content
(approximately 1-2-0). There is some question about the long-term
effects of using sewage sludge products in the garden, because
heavy metals, such as cadmium, are sometimes present in the
sludge. However, all sewage sludge must be analyzed for heavy
metals and meet EPA standars before it can be sold for soil
The following table shows the approximate nutrient
content of manures and suggested yearly rates of application per
1000 square feet of garden area. Rates given are for materials
used singly; if combinations of two or more materials are used,
the rate should be reduced accordingly.
|Type of Dry Manure
Compared to synthetic fertilizer formulations, organic
fertilizers contain relatively low concentrations of actual
nutrients, but they perform other important functions which the
synthetic formulations do not. Some of these functions are:
increasing organic content of the soil; improving physical
structure of the soil; and increasing bacterial and fungal
Fertilizers Combined with Pesticides
The major reason for buying a fertilizer combined with a pesticide is
convenience. It is very convenient to combine everything you need
in one application, but it is also very expensive. The problem is
that the timing for a fertilizer application often does not
coincide with the appearance of a disease or an insect problem.
And, in the case of a number of turf grass diseases, a primary
cause of disease infestation is merely a lack of proper
A fertilizer-insecticide combination, when applied at
the proper stage of a pests life-cycle, can do an adequate
job of controlling the turf pest while also giving the grass "a
shot in the arm" to help its recovery. However, fertilizers
with pesticides intended for use with turf or ornamentals should
not be used in the vegetable garden where it may contaminate food
crops. Always read the label carefully.
Fertilizers come in many forms. Different formulations are made to
facilitate types of situations in which fertilizer is needed.
Packaging on all formulations must show the amount of nutrients
contained, and sometimes it tells how quickly a nutrient is
available. Some of the formulations available to the homeowner
are: water-soluble powders, slow-release pellets, slow-release
collars or spikes, liquids, tablets, and granular solids.
Liquid fertilizers come in a variety of different
formulations, including complete formulas and special types that
offer just one or two nutrients. All are made to be diluted with
water; some are concentrated liquids themselves, others are powder
or pellets. Growers of container plants often use liquid
fertilizers at half the recommended dilution twice as frequently
as recommended so that the plants receive a more continuous supply