Evaluating the Costs and Benefits of Organic Amendments
One of the benefits of cereals in rotation is the opportunity to include cover crops and organic amendments into the rotation. Livestock farmers have always realized the value of manure in building soil fertility and supporting crop production. Today, a wide range of organic amendments—many sourced from outside agriculture—are available to crop producers. These materials can improve soil fertility, boost organic matter, enhance microbial activity, and support sustainable cropping systems, especially when they are combined with cover crops after cereal harvest.
There are many options for solid and liquid organic amendments available, however, not all amendments are created equal. Each product has unique characteristics, and the best choice depends on the specific needs of the field, logistics of application, and, of course, cost.
Guaranteed Analysis
Many products currently available in Ontario are registered under the Canadian Food Inspection Agency (CFIA) and carry a label guaranteeing minimum nutrient content. In practice, materials often contain more nutrients than listed, so sampling during application is essential for accurate nutrient credits and planning. Although CFIA-registered materials are classified as fertilizers, they are organic amendments and should be managed using the same 4R nutrient stewardship principles as manure. The 4R nutrient stewardship principles include right source, rate, place and time. Application of any material containing crop nutrients should never occur on frozen or snow-covered soils.
Evaluating and comparing options
In the current economic environment, where fertilizer prices are high, it may be advantageous to explore potential organic amendment options to supplement fertilizer. Trading manure for straw or purchasing manure from a livestock neighbour is ideal but often not an option. Examples of current options include livestock or municipal compost, pelleted, ashed or pH-enhancing biosolids (i.e., N-Viro/N-Rich), and anaerobic digestate. Table 1
compares various products available to non-livestock farms. While the values for these products are based on actual analyses and costs, the comparison is meant to provide an example of how products can be compared to assess which is the best fit for a particular farm. Each of the products compared, except the compost, are CFIA registered organic fertilizers. In this example, the target is to fulfill phosphorus needs for a planned corn crop while enhancing overall nutrient balance and soil organic matter.
The cost/lb of estimated available nitrogen, phosphorus and potassium provides a comparison for fertility value, based on spring 2026 fertilizer prices. Although manure value based on current (July) fertilizer prices has increased, the product and transportation costs have also increased resulting in similar cost per pound of amendment. The micronutrient value of these organic amendments has not been included since not every field requires micronutrients. Similarly, organic matter provides greater value to fields with poor soil health than fields with regular manure application.
Each of these products can supply the phosphorus needs for the corn crop, but their differences matter. How important is the nitrogen component and how will application timing affect the N value? Consider other goals based on soil test levels—extra organic matter to build soil, or a product that adds micronutrients or helps raise pH where required.
Table 1. Comparing various organic amendments for nutrients, composition and value.
Observe nutrient balance too. Biosolids often have very little potassium, potentially requiring supplementing with inorganic sources. Some biosolids also contain high levels of calcium, aluminum, or iron, which can tie up phosphorus and make it less available, especially in low or high soil pH conditions. As a rule of thumb, it is safe to assume with biosolids containing high iron (Fe) and/or aluminum (Al), that only about 20% of the phosphorus is available in the first year (compared to about 40% + in manure) and may require using a starter fertilizer to meet crop needs. Over time, the rest will become available, however, this can take months or even years depending on soil characteristics, including pH, microbial activity, moisture, and temperature.
Cost and logistics can also influence product choice. The dairy compost in this example can’t economically meet phosphorus needs, but reducing application to 5 ton/ac would provide similar soil health benefits and can be complemented with commercial fertilizer to match crop nutrient needs. Ashed biosolids would economically build phosphorus but with limited benefit to balancing soil fertility or improving overall soil health.
Cereal harvest is underway, providing an ideal opportunity to incorporate organic amendments into the crop plan. With so many choices, it is important to focus on farm needs; considering what each product adds (or lacks), and the cost and logistics of procuring and applying the material.
