Farm Progress

Organic fertilizer options available to all

Roy Roberson 2

February 12, 2010

7 Min Read

The continued volatility in price of fertilizer, combined with heightened regulatory scrutiny, will leave many growers scratching their heads as to which way to go to fertilize their 2010 crops.

Conventional farmers and organic farmers share a need for a low cost, highly efficient source of nutrition for their crops. Many of the fertilizers that meet organic certification may also work for conventional farmers who are looking for a low-cost, readily available source of N-P-K for their farms.

NORTH CAROLINA STATE Extension Agent Jeremy DeLisle says organic fertilizers can help conventional growers.

Two broad choices are available for conventional growers, organic and synthetic. For organic farmers, only the organic option is available.

Jeremy DeLisle, an Extension agent in western North Carolina, speaking at the recent North Carolina-South Carolina Fruit and Vegetable Growers annual meeting, says, “Transitioning to organic farming produces some soil fertility challenges that transcend the use of conventional bulk fertilizers to achieve optimum soil fertility.”

Organic farmers can and do use composts of plant and animal materials and uncomposted plant materials are allowed under Federal NOP (National Organic Program) guidelines. Raw manure can be used, but must be applied at least 120 days prior to harvesting most crops.

The most commonly shared manure-based fertilizer used by both conventional and organic farmers is chicken litter. Nutrient component varies widely from one chicken farm to another and there is variation from one poultry house to another on the same farm.

A typical load of chicken litter might contain something close to 75 pounds of nitrogen, 27 pounds of phosphorus and 33 pounds of potassium per ton. DeLisle gave an example showing that a ton of broiler litter from a North Carolina poultry house could contribute 15 pounds of ammonium, which would be available immediately for plant uptake.

The example might also contain 60 pounds of organic nitrogen, but only 30 percent or about 18 pounds of N was available to plants over the course of the first season.

The sample contained 21 pounds of phosphorus and 26 pounds of potassium, of which a producer should expect approximately 70 percent to be available in year one.

DeLisle stressed that having a waste analysis performed on the sample is the key to managing applications properly.

Dairy and beef manure are also commonly used fertilizer sources. Dairy manure, like chicken litter will vary in nutrient makeup, but will typically contain 10-15 pounds of NP and K per ton. Beef manure is consistently higher in nutrient content than dairy manure with 20-25 pounds of nitrogen and phosphorus and 30 pounds of potassium.

One of the more popular families of fertilizers used by organic farmers is plant-based fertilizers, primarily plant meals. All of these materials are low in N-P-K content and would not be sufficient as a stand alone fertilizer in either organic or conventional crops.

Soybean meal has 6-1-4.2 percent, respectively, nitrogen, phosphorus and potassium. Cottonseed meal is 6-2-1, alfalfa meal is 4-3-1 and kelp meal is 1-0-2. Any of these meals can be used on organic crops, regardless of whether they came from plants grown certified organic. However, none of these meals can be used on certified organic crops, if they come from GMO crops.

Animal-based fertilizers available to both organic and conventional growers include blood meal, bone meal, feather meal and fish meal. Of these, feather meal (13-0-0) is highest in nitrogen and bone meal (1-13-0) is highest in phosphorus. Fish meal has a 9-3-1 percent NPK makeup and blood meal is 12-0-0.

Like cottonseed meal, these animal-based fertilizers will be slow release and the nitrogen component will not be immediately available to crops. Conventional growers using these products as fertilizer supplements or boosts, and organic growers using animal-based fertilizers, need to understand these materials are best used when combined with cover crops, rotation strategies and other cultural practices that take advantage of their slow release characteristics, DeLisle says.

Mineral-based fertilizers that are approved for use on organic crops are much closer to the fertilizers used on conventional farms. Organic growers need to double check these materials to be sure they are on the national list of approved chemicals for certified organic farms, DeLisle stresses. Even though these products may have on the label OMRI-approved, occasionally these materials don’t make it onto the national list, he adds. OMRI is Organic Materials Review Institute. The OMRI Products List is a directory of all products OMRI has determined are allowed for use in organic production, processing, and handling. Only products that have passed this review are included in the OMRI Products List and can display OMRI Listed Seal — the organization’s registered certification mark.

Sodium nitrate (16-0-0) is available to organic farms, but can only comprise 20 percent of the total N used in the certified organic system. Also known as Bulldog Soda, this product can burn plants, but is quickly and readily available to plants. DeLisle points out that this material, like many of the organically approved products, is difficult to find these days.

Rock phosphate is another option. It is low in phosphorus (0-3-0), but has a high (23 percent) calcium content. Likewise, potassium sulphate is high in potassium (0-0-50), but also has a high (18 percent) sulphur content. For specific crops under specific soil conditions these materials may be good options for either conventional or organic farms.

“For growers considering transitioning to certified organic production, I sometimes recommend they get soil testing done and apply conventional fertilizer to get the soil up to where it needs to be, then let it stay out of production for the three-year requirement to meet organic certification. In some cases investing a fourth year is cheaper than slowly building soil nutrition up with fertilizers approved for organic production,” DeLisle says.

Greensand is another option for both organic and conventional farmers because it has a good concentration of a number of micronutrients. It has good potassium content (0-0-7) and is a good source of slow release calcium.

Greensand is a sand or sediment that consists of dark greenish grains of glauconite that is usually mixed with clay or sand. It is a natural mineral that opens up tight soil and binds loose soil. It is mined most intensively in New Jersey, Arkansas and Texas.

Gypsum (0-0-0) is also a good source of calcium (23 percent) and sulphur (17 percent). Gypsum from discarded building material and other sources is commonly used in the upper Southeast as a supplemental calcium source for Virginia type peanuts.

Compost is a commonly used practice for small acreage organic farms. It is low in nutrient value, but on both conventional or organic farms, it brings in a good source of micronutrients, building soil biological activity and increase cation exchange capacity, according to DeLisle. Cation exchange capability is the soil particle’s ability to hold on to the nutrients needed by plants. Compost is sort of like a glue to bind nutrients to the soil, DeLisle explains.

Among the numerous data on soil test samples, most experts agree cation exchange is the least understood. Any element with a positive charge is called a cation and, for agricultural purposes, it refers to the basic cations, calcium (Ca+2), magnesium (Mg+2), potassium (K+1) and sodium (Na+1) and the acidic cations, hydrogen (H+1) and aluminum (Al+3). The CEC refers to the total amount of these positively charged elements that a soil can hold.

The cations are held on "exchange sites" where one cation can be exchanged for the same type or a different cation. The CEC is expressed in milliequivalents per 100 grams (meq/100g) of soil. The larger this number, the more cations the soil can hold. A clay soil will have a larger CEC than a sandy soil. In the Southeast, where there are highly weathered soils, the dominant clay type is kaolinite, which has very little capacity to hold cations compared to other clays.

In some areas of the Southeast one or more of these organic sources of fertilizer are available to farmers. With today’s volatility in fertilizer costs and other input costs, these may be good options for conventional farmers to consider.

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