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ASK THE EXPERTS

Using organic fertilizers

POSTED: April 23, 2014 4:00 a.m.

Many home gardeners and small-scale producers have a growing interest in organic production.

Defining what "organic" means can vary from one person to the next, but generally the intent is to avoid using synthetic or man-made inputs, such as pesticides or fertilizers.

On a larger scale, growing organically is defined by the terms of the USDA's National Organic Program. It tasks an outside organization, the Organic Materials Review Institute, or OMRI, with deciding which products are available to organic gardeners and producers.

If you decide to garden by organic standards, it doesn't mean that you are confined to only animal manure for your fertilizer options. All organic-certified fertilizer products are listed on the OMRI website, www.omri.org. Here you will see there are a multitude of organic fertilizers available for home use.

It is helpful to understand that organic fertilizers differ in several ways from conventional fertilizers. Most organic fertilizers have lower concentrations of essential elements.

The three main essential elements are listed on fertilizer labels as three numbers, which are percentages of nitrogen-phosphate-potash. A conventional fertilizer like ammonium nitrate is 30-0-0, but an organic fertilizer such as blood meal or feather meal will only have around 12-percent nitrogen.

Most organic fertilizers also have slower release rates than conventional fertilizers.

Nitrate fertilizers contain nitrogen that is immediately available for plant uptake and ammonium fertilizers only take one to six weeks to break down enough for absorption.

Many organic fertilizers take from one month to as much as two years for the nutrients to become plant-available.

Organic fertilizers are often more expensive per unit of nutrient.

Urea nitrogen, a conventional fertilizer, costs around $2.60 per pound of nitrogen. Organic fertilizers at the low range of the price scale, such as feather meal, cost about $11.50 per pound of nitrogen. On the high-end, an organic fertilizer called fish emulsion (5-1-1) will set you back about $41 per pound of nitrogen.

If you are in the market for organic fertilizers, here are some that you may encounter:

• Fish emulsion (5-1-1) is a liquid fertilizer made from ground-up fish parts. It has a one to four month release time and is expensive at around $41 per pound of nitrogen. It can be smelly if not deodorized.

• Feather meal (12-0-0) is a relatively inexpensive organic fertilizer at $11.50 per pound of nitrogen. It has a release time of at least four months.

• Blood meal (12-0-0), a by-product of slaughter houses, has a one to four month release time and costs around $14 per pound of nitrogen.

• Fish meal (10-6-2) has a one to four month release time and costs around $22 per pound nitrogen. You may only consider this if you need phosphate in your soil.

• Bone meal (4-12-0; plus 22 percent calcium) can be a good choice if you need phosphate. It has a one to four month release time and costs $18 per pound of phosphate.

• Rock phosphate (0-20-0; 20 percent calcium) has a three-plus years release time and costs around $5 per pound of phosphate.

• Green sand (0-0-7) costs $14 per pound of potash and has a release time of at least four months.

• Sulfate of potash (0-0-50) has a one month release time and has a low cost of $3 per pound of potash.

When using organic fertilizers, always rely on soil test results when deciding which one to use. As you can see, you can easily waste a lot of money picking the wrong fertilizer and applying nutrients not needed in your garden.

Clark MacAllister is the Dawson County extension agent. For more information, call (706) 265-2442.

 

 

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