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Organic vs. manufactured fertilizers
Renewed concern about the environment has stimulated
interest in the use of organic fertilizers. As a result, there
is a debate about the qualities of organic versus manufactured
fertilizers. Primary considerations in selection include release
rate, cost and soil-building effects.
Organic fertilizers are commonly processed from various
animal and plant by-products, like poultry feathers, manures and
treated sewage sludge. These materials have slow release rates,
requiring soil microorganisms to break down the material into
chemical forms plants can use. Approximately half or less of the
nitrogen is released for crop use the first year. A significant
advantage of organic products is improvement in soil organic
content, which is key to successful Gardening in Colorado's
soils.
Organic fertilizers are comparatively low in nutrient
content so they require significantly larger volumes. Nutrient
release rates are slower in cool or dry soils. If you rely
solely on organic materials and your soil is low in organic
matter, lawns and Gardens often will appear pale green. This
indicates the nitrogen level is low.
On the other hand, manufactured nitrogen fertilizers are
normally made from petroleum or natural gas. Typical release
rates vary from a few days to a few weeks, giving a quick
response after fertilizer application. They also may require
some processing by soil bacteria. The phosphate and potash in
manufactured fertilizers generally are processed from rock
deposits. Costs are comparatively low to moderate.
Because manufactured fertilizers are relatively high in
nutrient content, only small amounts are required. Overapplication causes leaves to become yellow or brown, which is sometimes known as "burning." On sandy soils, an overapplication of nitrogen can leach into groundwater.
Both types of fertilizer will pollute our groundwater, lakes
and streams when spilled or spread onto streets, sidewalks and
driveways. Neither will pollute when correctly applied to lawns
and Garden soils.
For more information, see the following Colorado State Extension fact sheet(s).
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