Horticulture Principles and Practices

4.4 FERTILIZERS
Fertilizer sources may be organic or inorganic. Most of the fertilizers applied in horticulture
are inorganic in nature.
4.4.1 ORGANIC FERTILIZERS
Organic fertilizers are derived from plant and animal residues. Sources of organic fertilizers
include animal droppings (or manure from the barnyard or poultry house, bird
droppings, and other animal wastes), dried blood, and bonemeal. Guano is an organic
fertilizer consisting of bird droppings collected off the shores of South American islands.
Other sources of organic fertilizers are cottonseed meal and liquid waste from meat- and
poultry-processing factories. One of the commonly used nitrogen fertilizers, urea (46-0-0),
is actually a synthetic organic fertilizer.
Organic fertilizers are not commonly used in horticulture for several reasons,
including the following:
Fertilizer
An organic or inorganic
material of natural or
synthetic origin applied to
the soil or plant to supply
elements essential to plant
growth and development.
1. They are bulky to handle, requiring large amounts of space to store the required
quantity.
2. Their nutrient content is low (low analysis). Large quantities are thus required to
provide appreciable amounts of the nutrients needed.
3. They are difficult to quantify and apply according to a specified rate of desired
amounts of nutrient elements.
4. The nutrients they contain are released too slowly. They are released as the
material decomposes, and decomposition is variable and dependent on the
environmental conditions.
5. They are difficult to apply uniformly.
6. They are applied only to the soil.
7. Their use is often accompanied by foul odor that could be slight or very intense
as is the case of fish emulsion.
8. Fresh manures need to be composted to avoid burning plants from the high salts
they contain.
9. Some sources such as sewage sludge may contain heavy metals (e.g., cadmium) that
are injurious to plants.
Although these disadvantages usually disallow organic fertilizers in horticulture,
the following advantages for use do exist:
1. Organic fertilizers provide nutrients as well as increase organic matter content of
the soil, thereby improving soil physical structure and microbial activity.
2. Composted manures are often marketed as soil conditioners.
3. They supply micronutrients in addition to macronutrients.
4.4.2 INORGANIC FERTILIZERS
Inorganic fertilizers are most widely used to provide supplemental nutrition to horticultural
plants during production in the field or in containers indoors. They are popular for
reasons including the following:
1. They are easy to store.
2. They have higher analysis than organic fertilizers.
3. They can be custom formulated for specific purposes.
4. Inorganic fertilizers are easy to apply and can be applied uniformly.
5. They are available in liquid and solid forms.
4.4 Fertilizers 117