Biochar’s remarkable properties make it incredibly useful for many agricultural applications, including improving plant productivity and water quality. But because biochar is so broadly applicable, you may be wondering exactly how to choose the right biochar for your application.
Here are some guidelines you can follow to choose the biochar that’s best for you.
Step 1: Set your project goals and do some research
During your initial planning, you should ask what you hope to achieve by using biochar in your application and do some research. You should also always check with your biochar supplier to make sure you are buying the right biochar for your needs.
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The properties of biochar can vary depending on its source material and how the biochar was produced. Here are tips for some of biochar’s common applications:
Increasing water retention
Look for biochar with a fine particle size, preferably one that is smaller than the particles present in your soil. This way, the biochar can fill in spaces within the soil to create tight pores that will hold water against gravity.
Increasing water infiltration
Look for biochar with a large particle size, preferably one that is larger than the particles present in your soil. This way, the biochar can pack with the soil in a way that creates large pores, which drain readily.
Increasing nutrient retention
Look for any nutrient studies that have been done on the biochar you’re interested in. These will give you a good idea of how the biochar will react with nutrients and other chemicals in your soil.
In most cases, biochar will improve the nutrient retention of your soil by preventing nutrients from leaching out while still making them available to plant roots. Biochar is especially effective when it has been “charged” with nutrients and beneficial soil biology beforehand or used in conjunction with nutrient-rich materials like compost.
Improving microbial activity
Biochar by itself does not contain any soil microorganisms, but it is an optimal habitat for them as biochar’s complex pore structure can safely house billions of beneficial soil microbes. Biochar’s carbon walls protect microorganisms from harsh soil conditions and allow them to increase in population when they interact with exudates that come from plants.
This symbiotic effect is one of biochar’s most important advantages for improving soil quality, and is most effective when biochar is blended with sources, like compost, that already contain nutrients and beneficial soil biology.
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Improving water quality
Look for nutrient and contaminant studies that have been done on the biochar you are interested in.
If the biochar can bind to nitrates, phosphates, heavy metals, and other pollutants, it may be excellent as a first step in improving your water quality for irrigation, livestock, or other applications.
Adjusting soil pH
Look for the liming value of the biochar you’re interested in. The liming value is a measure of how much soil pH can be increased, which is useful for acidic soils. You may be able to obtain these lab results from the supplier.
Doing so will give you an idea of how the biochar may affect your soil and how you can potentially reduce the amount of calcium needed for your project.
Tying up heavy metals
Look for any studies on heavy metals that your supplier has conducted with their biochar products. Biochar can directly bind to these metals and reduce their concentration and availability in the soil. Biochar can also reduce the availability of heavy metals by increasing soil pH, which decreases the availability of heavy metals that are more soluble in acidic environments.
Biochar’s complex pore structure and high surface area make the material an ideal medium for binding excess salts from overfertilization, irrigation, or deicing. To reduce soil salinity, look for biochars that have low salt content and large particle size to increase water infiltration. In general, the salt content in biochar increases with ash content, so make sure that the biochar you select has low ash content. You should look for this value in lab results provided by the supplier.
Step 2: Determine the amount of biochar you need
When you have determined your goals, you should plan out how much biochar you need for your application.
As a first step, check with a supplier to determine the volume of biochar best suited for your needs. This can be done by checking application rates for a specific use and soil quantity.
Next, make sure the supplier can deliver enough material for you to complete your project, and that the biochar that you obtain will have consistent quality.
Step 3: Determine the quality of biochar you need
Now that you have determined how much biochar you need, you should ensure that the biochar you buy is of a consistent and high quality. You can look into several factors, including:
Make sure the biochar you are purchasing has the same properties whether they are obtained from different batches or from different parts of the same batch. Ask for a product data or spec sheet along with lab analysis to ensure your biochar will have consistently high-quality results.
Make sure the feedstocks (also called source materials) are clean, free from contaminants, and sourced from sustainable and responsible ingredients. You should also check if the biochar is certified biobased.
The USDA defines “biobased products” as goods that are “derived from plants and other renewable agricultural, marine, and forestry materials and provide an alternative to conventional petroleum derived products.” Products certified through the USDA BioPreferred® Program, which aims “to increase the purchase and use of biobased products,” carry the “USDA Certified Biobased Product” label.
Shipping and storage methods
Make sure the finished product is stored and shipped properly to keep it free of any contaminants. Although biochar can be shipped in bulk dump trailers, bulk bag “super sacks” are preferable in most situations as they are easier to handle.
The shipping method is generally determined by the type of project and the application equipment that is available.