Organic fertilizer options available to all

Organic Fertilizer

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.

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.

Source : http://southeastfarmpress.com

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Assessing Soil Acidity

By  Richard Fisher, E. M Hutton, Avilio A. Franco, Anthony Juo, Donald Kass, and Dale Evans

What Is an acid soil? 

Soil scientists use ranges of pH values to describe the acidity of soils. Soils in the pH range of 6.8 to 7.2 are considered neutral. Any soil with a pH of less than 6.8 is considered acidic, and any soil with a pH of more than 7.2 is considered alkaline. Soils with a pH of less than 35 or more than 10 rarely support plant growth Acid soils are described as "mildly acidic," "moderately acidic," and "strongly acidic" as pH values decrease. Mildly and moderately acid soils may not be detrimental to the growth of most plants.

Regions in the tropics in which soils are likely to be acid or low in bases such as calcium and magnesium.

Source: Caudle (1991).

The term "acid soil" is usually reserved for soils in which many types of plants have difficulty growing. This manual is concerned with these strongly acidic soils. They are characterized by a pH of less than 5.5 and one or more chemical problems that limit plant growth. Such problems may include (1) toxic levels of available aluminum, (2) toxic levels of available manganese, and (3) infertility due to insufficient levels of other elements important for plant growth, particularly calcium and phosphorus. Strongly acidic soil conditions limit the kinds of plants that can grow, the productivity of those plants, and the efficiency of fertilizers applied to increase plant productivity.

What is pH? 

The acidity of a soil is assessed in terms of the acidity or alkalinity of the soil solution - the moisture in the soil - as measured in units of pH. The soil solution contains chemical elements in dissolved ionic form. Many of these function as essential plant nutrients, taken up from the soil solution by the roots of plants.

The acidity of a soil results from the relative presence or absence of acidic ions, such as hydrogen (H+), in the soil solution. Soil acidity increases with the increased presence of these ions and decreases with the increased presence of basic ions such as calcium (Ca++) and magnesium (Mg++).

The acidity of a soil solution is expressed on the pH scale as the negative logarithm of the hydrogen ion (H+) concentration. Because the pH scale is mathematically logarithmic, a pH change of one unit represents a ten-fold change in the acidity or alkalinity of the solution being measured. Thus a soil with pH 5 is ten times more acidic than a soil with pH 6. A soil with pH 4 is ten times more acidic than one with pH 5 and 100 times more acidic than a soil with pH 6.

How do soils become acidic?

Soils become acidic through the normal leaching action of rainfall over long periods of time. As rainwater moves down through the soil, it absorbs carbon dioxide from the soil atmosphere and forms weak carbonic acid. It also acquires weak organic acids as it encounters soil organic matter. This acidic solution attracts basic ions, such as calcium (Ca++), magnesium (Mg++), potassium (K+), and sodium (Na+), detaches them from the soil exchange complex, and leaches them from the rooting zone. As these basic ions are leached, they are replaced by acidic ions of hydrogen (H+) and aluminum (Al+++). Over long geologic periods, soils in warm climates with high rainfall become severely depleted of basic ions and strongly acidified. Many of these acid soils also have levels of available aluminum or other ions that limit plant growth.

At a pH of 5.5, a soil generally does not inhibit the growth of crops or trees because it contains little available (exchangeable) aluminum. As pH decreases to 5.1 or lower, the amount of available aluminum increases and begins to interfere with the uptake of calcium and phosphorus, adversely affecting plant growth.

The soil taxonomy classification of the United States Department of Agriculture labels most tropical soils with a pH of less than 5.5 as Oxisols or Ultisols. The Food and Agriculture Organization (FAO) calls these Ferralsols and Acrisols. The Oxisols, with aluminum saturations of 79 to 89 percent, are more harmful to leguminous trees and crops than are the Ultisols, with aluminum saturations of 49 to 64 percent. There are also some strongly acidic Entisols (called Arenosols by FAO), Inceptisols (classified as Cambisols, Plinthosols, and Gleysols by FAO), and Andisols (Andosols).

How does soil acidity affect the availability of nutrients? 

Plant roots obtain nutrients from the soil solution, and that solution's chemical composition is affected by its pH. Nutrient availability is greatest in soils with a pH between 55 and 65. When the soil solution falls outside this range, plants often show signs of nutrient deficiencies.

In alkaline soils at a pH above 7.0, phosphorus, iron, zinc, boron, and copper become less available to plants. In acid soils at a pH below 5.0, phosphorus and molybdenum become less available and soil nitrification slows down. Some nutrients - such as calcium, magnesium, and potassium - may be lost, and high levels of available iron or aluminum may lead to the formation of insoluble phosphate compounds, dramatically reducing the level of phosphate available to plants.

The two most important indicators of acid soil conditions that are severe enough to limit plant growth are low pH and high levels of available aluminum. Indeed, aluminum toxicity and soil infertility are often associated. In soils with a pH of 5.1 or lower, aluminum levels often constitute more than 50 percent of the cation exchange complex. Manganese toxicity can also occur in a soil with a pH of less than about 5.5, but manganese toxicity is not as common as aluminum toxicity.

How do you measure soil acidity? 

The best way to determine whether a soil is strongly acid is to consult a soil scientist. Failing this, a general soil survey map may be useful. Such a map may include specific information on soil pH and the degree of aluminum saturation. Otherwise, as a general "rule of thumb," soils classified as Oxisols or Ultisols are likely to be strongly acidic in tropical climates.

If you cannot consult a soil scientist or a reliable soil map, you may need to collect soil samples and have them analyzed. Take separate samples at depths of 0 to 20 cm, 20 to 50 cm, and 50 to 100 cm below the soil surface. The subsoil is normally the best indicator of acidity because the surface soil (at 0 to 20 cm) is often affected by recent management. Altogether, you will need about 10 separate samples at each depth for each distinct soil area in your site. Mix together the 10 samples for a specific area and depth and take a small subsample of the mixture.

You may be able to send your samples to a soil laboratory for analysis of pH and available aluminum levels. Alternatively, you can analyze the pH levels of your soil samples using a portable pH meter, colorimetric test kit, or test strips. Mix each subsample with an equal volume of pure water (rain water is preferable to tap water if deionized water is not available). After mixing, allow the soil particles to settle for a few minutes and then measure the pH of the solution above the soil particles.

Equipment for measuring pH is available by mail order or from retail outlets that specialize in agricultural or scientific supplies. Colorimetric pH test kits are fairly inexpensive but are less precise than electrochemical instruments. There is no simple field test for available aluminum, but if the pH is below 5.0, then available aluminum is likely to be high.

An alternative to analyzing the soil is to observe plant growth as an indicator of soil conditions. What kinds of plants are growing in the soil? The presence of plants that tolerate acid soils such as imperata grass, bracken ferns, and Stylosanthes species-is an indication of acid soil conditions. If crops are growing well, the soil is probably not highly acid. If, on the other hand, there are problems with beans, cotton, or maize crops, then soil acidity may be the culprit. Phaseolus beans (not cowpea types) are particularly sensitive to aluminum toxicity if they are growing well, aluminum may not be a problem.

How do you Interpret the results of a soil analysis? 

An analysis of soil nutrients is often expressed in terms of milliequivalents per 100 g of soil (meq/100 g). An equivalent expression is cmol charge/kg. Values given as milliequivalents per 100 g of soil may be converted to parts per million (ppm) as follows:
1 meq/100 g of K+ (potassium) = 391 ppm
1 meq/100 g of Al+++ (aluminum) = 90 ppm
1 meq/100 g of Mg++ (magnesium) = 122 ppm
1 meq/100 g of Ca++ (calcium) = 200 ppm
1 meq/100 g of Na+ (sodium) = 230 ppm.

 Phosphorus content is usually expressed as parts per million. Most field and vegetable crops will respond to additions of phosphorus and potassium fertilizers when soil phosphorus (sodium bicarbonate [NaHCO3]-extractable) is in the range of 8 to 15 ppm and exchangeable soil potassium is in the range of 60 to 100 ppm. Soil phosphorus above 25 ppm is considered adequate for maize. One important measure that can be obtained from soil test results is the percent of aluminum saturation. This value compares the amount of exchangeable aluminum in the soil with the sum of aluminum plus exchangeable bases, as in the formula:

 Al / (Ca + Mg + K + Na + Al) x 100 = % Al saturation

In most cases, not all of these elements need to be analyzed. As a minimum for calculating percent aluminum saturation, the content of aluminum, calcium, and magnesium should be determined.

Plant species and varieties differ in the amount of aluminum saturation they can tolerate: above that limit, plant growth is reduced. Generally, cowpea-type beans, males, rice, and cassava have high tolerance to aluminum (70-100% saturation), whereas phaseolus-type beans, sorghum, soybeans, and wheat have low to moderate tolerance (0-70%), and cotton and maize have low tolerance (0-40%). Some nitrogen fixing tree species are known to tolerate high levels of aluminum in the soil, but the critical level for many species is not known. Controlled experiments are required to provide this information for a number of tree species and, in some cases, for particular varieties and provenances.

If plants show stunting, crinkled leaves, or leaves with small brown spots, manganese toxicity may be suspected. To determine manganese toxicity, apply a 5 percent hydrogen peroxide solution to a soil sample: if the solution fizzes (makes bubbles), manganese toxicity may be a problem.

Source : http://www.fastonline.org

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