Biochar is finely chopped wood charcoal that becomes an integral part of a healthy soil ecology thereby improving overall soil fertility. Adding biochar to your soil, compost, or livestock bedding reduces nutrient loss, stimulates the growth of essential soil microorganisms and increases moisture retention while sequestering carbon for many years after application.
For best results in the garden, dry biochar should be “charged” before direct application to the soil. Biochar acts like a sponge absorbing water and nutrients while providing a matrix for microorganisms to colonize. To avoid drawing fertility and microorganisms from the soil in the short term, saturate (or charge) the biochar with nutrition before application.
Here are a few of the most common ways to charge your biochar:
Mix with Compost: This is the quick and dirty method. Mix five or more parts finished compost to one part biochar. Add water to form a moist but fluffy soil amendment. Dry biochar will absorb a surprising amount of water so don't be stingy, but avoid a slurry. The exact amount of water is not critical. Let sit for a day or so before adding to garden soil to allow the biochar to absorb the nutrients and microorganisms in the compost.
Use Biochar In Your Compost Pile: This is a great no fuss method. Keep a covered container near the compost pile and add a few shovelfuls with each new layer. Use finished compost as usual and your biochar will move with the compost. In compost piles that use fresh animal manures, the biochar will help prevent nitrogen loss from leeching or evaporation and thus improve the quality of the compost.
Mix with Compost Tea: Among biochar aficionados, this is the preferred way of charging. Put biochar in a bucket and add compost tea until saturated. Use immediately. Good aerated compost tea is the best way to build the diversity and populations of beneficial organisms in your soil and insures that the biochar imparts the greatest immediate benefit to the soil.
Use in livestock bedding: Spread a thin layer of biochar on the floor of chicken houses or livestock shelter before adding additional bedding. Biochar absorbs the urea and the biology of manure will fix the nitrogen and phosphorous in the bedding to greatly reduce odor and retain nitrogen. Like adding to the compost pile, this is an easy and effective way to use biochar. It also can be used in animal feed to improve digestive health.
Nutrient/Water Charging: Put biochar in a bucket and saturate with diluted fish/kelp emulsion mix. Adding ½ cup of molasses per five gallons of the liquid fish/kelp mix will help stimulate microbial action. Use immediately. This method does not add active microbe cultures to the soil, but will stimulate microbial populations already resident in the soil. It is an effective means of distributing fertilizer in a way that minimizes runoff. Particularly useful in boosting fertility in mature gardens that contain an abundance of organic matter and microbes or in sandy soils where water and nutrients tend to leech.
As you can see, there are many ways to charge biochar. Like so many things we use in the garden, there are few hard and fast rules.
The unique properties of biochar make it particularly useful in many applications at varying concentrations depending on circumstance. Here are some of the typical use cases and application rates:
In Typical Garden Soil: The general rule of thumb is that one cubic foot of biochar is sufficient to improve thirty square feet of garden bed. Generally this works well in most situations.
In Sandy Soil: In loose sandy soils that are prone to drought or that tend to leach nutrients, use double the standard (one cubic foot of biochar for fifteen square feet of garden bed. Combined with regular compost additions, biochar can dramatically improve soil health in heat and drought conditions.
In Wet Heavy Clay Soils: Use half the standard rate (one cubic foot of biochar per 60 feet of garden bed) in conjunction with generous additions of organic matter, sand, and/or basalt dust for several seasons in succession to improve loft and increase microbial activity. The goal is to allow the soil to develop soil health and friability over time.
In Waterlogged Soil: Do not use biochar in situations where the soil regularly supports standing water or is marshy. Biochar will exacerbate this condition.
Organic Container Growing: Because of biochar's ability to hold on to water and provides microorganism shelter from the extreme fluctuations in moisture availability in a container environment, biochar is a valuable addition to traditional growing mediums. More water stays in the pot along with the nutrients when feeding container grown plants. Combined with standard compost tea, container plants can receive many of the benefits bedded plants enjoy. Typically, replace 10-15% of the growing medium with biochar for the best results.
Tree Planting: As with container plants, newly planted trees benefit from the superior water holding ability. Adding biochar with the other standard amendments is a simple way to improve establishment success. Add one third to one half the volume of compost per hole and mix soil and amendments as usual. Water newly planted tree thoroughly.
Hydroponics: Biochar is very a valuable medium in hydroponic growing systems. It simulates biological action and concentrates nutrients around plant roots better than typical peat or other organic mediums alone. For more information on using biochar in hydroponics see this article from Science in Hydroponics.
Livestock Feed: Beyond the benefits of using biochar in livestock bedding, biochar can be used as a feed supplement to improve digestive health and feed efficiency. See this industry article from FEECO or this study published in the NIH's PubMed