Frequently Asked Questions: Organic Soils Section

Soil Fertility:

• Why are conventional fertilizers such as ammonium nitrate, urea and triple superphosphate prohibited on certified organic farms?
• What nutrient sources are available to organic farmers?
• How can I maintain soil nitrogen levels?
• What can I use to add phosphorus and potassium to my soil?
• How can I raise the pH of my soil?
• Why is it important to maintain balanced levels of calcium, magnesium and potassium in soil?
• Is human sewage sludge permitted under the organic standards?
• What is a nutrient management plan and are organic producers required to have one?
  

Why are conventional fertilizers such as ammonium nitrate, urea and triple superphosphate prohibited on certified organic farms?
These concentrated, highly soluble fertilizers tend to inhibit biological processes and are more readily leached from the soil. To promote a slow and balanced uptake of nutrients by the plant, natural mineral fertilizers that release nutrients through an intermediate process (e.g., weathering or the activity of microorganisms) are preferred.

What nutrient sources are available to organic farmers?
Organic farmers use nutrients from both organic and inorganic sources. The most common organic nutrients ("organic" meaning derived from recently living organisms) are manure, compost, and plowdown crops. By-products of the seafood industry, such as fish meal and crab meal, and of the conventional meat industry, such as bone meal and blood meal are also used. Not all organic sources of nutrients are allowed in certified organic production systems. For example, compost made from municipal solid waste may not be allowed, depending on the feedstocks used, and sewage sludge, whether composted or not, is prohibited.

Inorganic nutrients are mostly derived from mineral deposits. There are a variety of mined minerals available for use on organic farms, including limestone, gypsum, rock phosphate, greensand and sul-po-mag. To be approved for use in an organic system, mined minerals must not have undergone any changes in molecular structure through heating or combining with other substances. Also, some mined minerals are not permitted for other reasons. For example, muriate of potash (potassium chloride), which is used extensively in the conventional agriculture industry, is prohibited in organic systems because of the danger of salt accumulation with excessive use.

Certifying bodies vary in which substances are permitted; check the Permitted Substances List of your organic standard to learn which organic and inorganic nutrient sources are acceptable.

How can I maintain soil nitrogen levels?
Most certifying bodies strongly suggest the incorporation of nitrogen-fixing legumes into the rotation. Alternatively, or in addition, composted animal manures and green manures can be used. Many specific soil amendments such as fishmeal, feathermeal, alfalfa meal and soybean meal (excluding GMO soymeal) may be used if they are free of contaminants.

What can I use to add phosphorus and potassium to my soil?
Phosphorus (P) removal via the export of food produced from the farm can lead to an eventual deficiency in P. Most certifying bodies recommend the creation of biologically active soil as the most efficient method of providing phosphorus for plant growth, as such the use of composted animal manures and green manures would be first options. The use of colloidal, soft rock, and hard rock phosphate is also permitted. With respect to potassium (K) wood ash (not contaminated with heavy metals); greensand; langbeinite; are rich sources of potassium that can be used in addition to animal and green manures.

How can I raise the pH of my soil?
Soil pH can be altered with the use of calcitic or dolomitic limestone, which is an excellent source of calcium.

Why is it important to maintain balanced levels of calcium, magnesium and potassium in soil?
Cations are the link between soil pH and nutrient balance. A predominance of acidic cations such as hydrogen (H+) and aluminum (Al+3) indicates acid, infertile conditions. Calcium (Ca+2), magnesium (Mg+2), potassium (K+), and sodium (Na+) are basic cations. Calcium is the dominant cation in fertile, near-neutral soils. For balanced fertility and optimum availability of plant nutrients, a soil base saturation (proportion of the soil's cation exchange capacity (CEC) that is occupied by exchangeable base cations expressed as a percentage of the total CEC of the soil) of 50-70% Ca, 8-20% Mg, and 2-5% K is usually recommended.

Does manure have to be composted before use on organic field crops?
Composting is a recommended practice in organic farming, and a requirement for using off-farm, non-organic sources of manure. Composting is recommended for the following reasons:
· Composting stabilizes the N in manure, and reduces loss after land application;
· Composting improves manure handling and friability;
· Composting reduces weed seeds and toxins (pathogens, pesticide residues, antibiotic residues, etc.), and
· Compost makes a greater contribution to SOM and longer-term soil fertility than applications of raw manure.

Is human sewage sludge permitted under the organic standards?
No, not at present.

What is a nutrient management plan and are organic producers required to have one?
A nutrient management plan is a document that denotes an integrated strategy and specific practices for how nutrients will be used in crop production. Producers benefit from developing a nutrient management plan because it helps ensure that crops are getting the nutrients required for optimal yield and quality, nutrient resources are being used in the most effective way, and nutrient pollution of soil and water is kept to a minimum. In many jurisdictions farms above a certain size (i.e., with more than a specified number of animal units) are required by law to develop and use a nutrient management plan. Where a plan is required by law, it usually must be completed by a trained nutrient management planner.