If you missed Bloom’s nutrient analysis presentation with recycled organics expert Ron Alexander, give it a listen! While there was simply too much material to capture all his talking points, here is a synthesis of some of his takeaways:
- Nutrient analyses serve to better understand the characteristics of a soil amendment, whether it’s a compost or biosolids product like Bloom. They can help explain if the soil amendment matches your soil/project requirements (hint: test your soil first!)
- Different labs can present nutrient analyses in different formats. Standardization of testing, units of measurement etc. is becoming more commonplace, but the formats can look quite different, and the test also depends on what is requested by the sample submitted.
- University extension programs and private labs are the most common source of testing of both soil and soil amendments. Regardless of whether you are testing soil or soil amendments, it’s good to look for labs that will not only provide the data but also some interpretations and recommendations. “As a scientist, I don’t always agree with interpretations, but they are a good starting point,” says Ron.
- Previously, soil amendments were utilized primarily to add carbon-based organic matter to the soil, but now there is a greater understanding of the suite of benefits they provide to help improve the physical, chemical, biochemical, biological or other characteristics of the soil, including micronutrients, slow-release macro-nutrients and more. As a result, over time more parameters have been included in soil amendment testing to assess for these different benefits.
Some key test parameters and how to think about them:
- Nitrogen (N): Total nitrogen includes ammonia, which is a volatile form of nitrogen, that will reduce as a product like Bloom ages. “Ammonia can plume off into the atmosphere, but air is 70% N – so that’s no big deal,” says Ron. “Too much ammonia can burn plants, however.” Nitrate is another form of mobile nitrogen, which readily dissolves in water, and is then easily picked up by plants. Nitrate nitrogen can attach to carbon, becoming slowly-releasing in nature. It must then be mineralize back into nitrate form, with the help of soil microbes, to make it available to plants.
- Phosphorus (P): “In many soil amendments, like Bloom, phosphorus is low in water extractable phosphorus. In fact, in biosolids-based products, phosphorus is even slower to release than nitrogen as it binds to the soil ion the presence of aluminum, iron and/or calcium. Highly concentrated forms of chemical P bind to the soil to lesser degree, and are therefore much more problematic in term of nutrient drift,” says Ron. Over time, ammonia in products like Bloom and compost reduce, as the ammonia attaches to organic matter, and is converted into slowly available forms of nitrogen.
- Potassium (K) is the only of the three primary essential plant nutrients that releases quickly from carbon-based soil amendments.
- C:N ratio was traditionally used to express maturity of a compost product. Above a 25:1 ratio can rob nitrogen from the soil. However, high nitrogen feedstocks can “fool” the test, so it is not always the best indicator.
- Moisture content: This percentage can also be somewhat relative in the sense that “55% moisture compost is a nice workable texture for a product like Bloom but would be very wet and clumpy for a compost product. It’s just the nature of the products’ composition,” explains Ron.
- Organic matter (OM) content: The higher the OM, the better, generally speaking. This is another parameter that can sometimes be affected by external factors; for example, soil amendments produced on concrete pads can result in higher OM content than those produced on a dirt surface. This is simply because soil is heavier than organic matter and can dilute its content in soil amendments. “Sand content will also drive OM content down,” says Ron.
- Sodium and chloride can be high in food waste compost and were added to test panels for these composts as a result. However, there is not much understood about the effects, but they are being studied.
- When testing soils, the mass is heated until the water is removed, then the soil is heated at a higher temperature until the OM is gone. Ash essentially is the remaining material (sand, silt, clay) that doesn’t burn off after the carbon and water have been removed.
- Bulk density is a measurement relating volume to weight, i.e., how much a cubic yard of material weigh.
- Heavy metals: Many are trace metals that are essential plant nutrients, such as copper and zinc. Iron for example improves the intensity of the green color in plant leaves. “Presence of metals alone is not something to necessarily be concerned about. Often these test an order of magnitude lower than a worrisome number,” says Ron. The EPA sets strict limits for heavy metals in biosolids products.
- pH: This is another tricky parameter as the pH of a product will not necessarily significantly affect the pH of the soil, as Bloom research has discovered. “Bark, such as the bark fines added to Bloom’s blends, can initially raise the pH, but this is not fixed and will be reduced within a few months,” explains Ron.
Units of measurement:
- Dry vs wet weight: Many parameters will be expressed as both dry weight and wet weight, or as received. Dry weight refers to the percentage of a nutrient in the material with the total water weight backed out, whereas wet weight/as received refers to the total percentage of a nutrient as it appears in a product. For a product like Bloom with a fairly high moisture content, these numbers can vary significantly. Organic matter is always expressed as dry weight basis, whereas the NPK numbers on fertilizer products (such as cured Bloom) are by law always expressed on an “as received,” wet weight basis.
- 10,000 PPM (parts per million) is equivalent to 1%.
- For stability, the lower the number the better (“like a golf score!” says Ron), whereas for maturity testing, the higher the number the better.
“If you receive an analysis from a product, make sure it’s not more than a few months old. As you begin to study nutrient analyses, you aren’t going to understand everything. Focus on what’s most relevant for your purposes, and ask questions of your lab,” concludes Ron.