A Fine Balance…Organic Soil Amendments and Fertilizers

Av Singh, Ph.D.

There are many schools of thought within the organic community on how to maintain soil nutrient balance. Traditionally, the organic farmer was solely reliant on nutrient recycling via plants (e.g., legumes in rotations, cover crops, green manures) and animals (e.g., dung and urine). Today, many organic farmers have specialized into either crop or livestock production and therefore cannot fully benefit from nature's free nutrient recycling services and instead must seek off-farm nutrient sources. Conventional producers often think organic farmers are limited to animal manures as their sole option for off-farm nutrients. In reality, it's quite the opposite. Organic producers may, in fact, be overwhelmed by the nutrient and mineral sources available to them. This article will define many of the common fertilizers and soil amendments used by organic producers.

Most certifying bodies strongly recommend that the use of composted animal manures, green manures, and crop rotation involving legumes be a first step at maintaining a healthy, biologically active soil. That being said - there are a number of commercially available materials that can complement an existing fertility program. Materials derived from organic wastes or mined minerals are readily available and desirable. Amendments are primarily chosen because they provide particular nutrients that are either deficient in the soil or are in high demand by the crop, however many organic amendments generally contain substantial amounts of other major and minor nutrients as well. Natural nutrient and mineral sources are often considered to have less risk of creating imbalances in the soil ecosystem or of causing pollution by overapplication than synthetic fertilizer sources. The terms fertilizers and soil amendments are often used interchangeably, but a distinction should be made. Generally, when you are applying a material primarily to provide nutrients to a crop it is considered a fertilizer. Alternatively, if the primary intention is to improve soil health then the material is often referred to as a soil amendment, despite having nutrient releasing benefits.

Prior to using organic amendments it is prudent to check with your certifying body the permissibility of any ingredient. Many "natural" products, especially organic by-products and wastes may be restricted because of the presence of heavy metals, antibiotics, or genetically modified organisms. Commercial fertilizer blends are often evaluated by the Organic Materials Review Institute (OMRI- www.omri.org), which publishes a list of generic and brand name materials that are acceptable for organic producers.

Fresh and composted manures vary widely in nutrient analysis, depending on what animal it originated from, what the animal was fed, and how the manure was handled. The list below will not present animal manures, rather it will emphasize alternative nutrient sources.

Much of the information above has been obtained from organic product distributors, standards from varying certifying bodies, and published literature (e.g., Start with the Soil by Grace Gershuny). But knowing what you want to use is only half the problem - finding it is the other half. The Atlantic Canadian Organic Regional Network (ACORN) in cooperation with organic agriculture specialists, Susan Mackinnon (PEI) and Claude Berthélémé (NB) have initiated a project that will help producers source certified organic amendments as well as provide information on rate of application and elemental analysis.

The organic producer has at their disposal the necessary tools to maintain the fine balance of a healthy soil. Internal nutrient recycling using animal and green manures or via commercial inputs are both options, but remember that prior to using any product you should check with your certifying body.


For more information please call the Organic Agriculture Centre of Canada at 902-893-7256 or email oacc@nsac.ca


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