Exploring organic options for soil fertility and health
Agronomic information from Ontario's crop specialists
Specialist, Ontario Ministry of Agriculture,
Food and Agribusiness
Livestock farmers have always recognized the value of manure in building soil fertility and supporting crop production. Historically, crop producers without access to this resource have looked on with envy. Today, though, a wide range of organic amendments—many sourced from outside agriculture—are available. These materials can improve soil fertility, boost organic matter, and support sustainable cropping systems.
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 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. Application of any material containing crop nutrients should never occur on frozen or snow-covered soils.
EVALUATING AVAILABLE OPTIONS
In a scenario where fertilizer prices are high, a producer might explore organic amendments to supplement fertilizer. Current options include dairy or poultry compost and pelleted, ashed or pH-enhancing biosolids (i.e., N-Viro/N-Rich). The target is to fulfill phosphorus needs for corn production while enhancing overall nutrient balance and soil organic matter.
Each of these products can supply the phosphorus needs of the crop, but their differences matter. Think about other goals depending on soil test levels—extra organic matter to build soil, or a product that also adds micro-nutrients or helps raise pH.
Watch nutrient balance, too. Biosolids often have very little potassium, potentially requiring supplementing with commercial fertilizer. 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, assume only about 20 per cent of the phosphorus in biosolids is available in the first year, and use a starter fertilizer to make sure the crop gets what it needs. Over time, the rest will become available, but 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 the example in this article 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 improving overall soil health.
With so many choices, it’s important to focus on farm needs, what each product adds (or lacks), and the cost and logistics. Picking the option that fits best will give the greatest return.
| Table 1: Comparing Products | Dairy compost | Poultry compost | Biosolids pellets1 | Ashed biosolids2 | N-Viro (N-Rich) |
| Dry matter % | 35 | 70 | 96 | 70 | 77 |
| ~Available N-P2O5-K2O (lbs/ton) | 4 – 4 – 13 – 1 (S) | 12 – 37 – 28- 7 (S) | 35 – 64 – 7 – 10 (S) | 0.2 – 218 – 13 – 3 (S) | 4 – 15 -79 – 59 (S) |
| C:N ratio | 22:1 | 8:1 | 7:1 | 15:1 | 21:1 |
| Organic matter (lbs/ton as-applied) | 125 | 311 | 1,400 | 17 | 432 |
| Ca- Al – Fe (lbs/ton) | 21 – 0.5 – 2 | 81 – 6 – 11 | 39 – 8 – 37 | 113 – 37 – 180 | 322 – 28 – 15 (ag index 23) |
| Rate to meet corn P2O5 target | 21 tons | 2.25 tons | 1.3 tons | 0.4 tons | 5.6 tons |
| N-P-K applied at target rate | 84 – 84 – 273 | 27 – 83 – 63 | 46 – 83 – 9 | 0 – 87 – 5 | 22 – 84 – 442 |
| ~ Cost/ton 3 | $40 | $110 | $95 | $120 | $105 |
| ~ Cost/ac3 at target rate | $800 | $250 | $123 | $48 | $600 |
| 1 This example uses Detroit pellets (Toronto pellets ‘NutriPel’ ~50 – 120 – 2 – 22S -77Ca – 6Al – 118Fe lbs/ton) 2 Phosphorus content will vary by location of origin. 3 Cost will vary with distance for transporting materials | |||||
