How much Biochar do I need?
This is the subject of ongoing studies. The degree of benefit clearly increases with the application rate.
If you are satisfied with a very rough estimate, we would venture that a target application rate of 5 kg/cbm would be sufficient to achieve these results in most gardens. However, there are substantial benefits related to soil biology at rates well below 1 kg/cbm. For adding with other soil mixes we recommend a blend of 5 - 10%. This FAQ includes information on how to use small amounts of biochar in your garden to best advantage.
How long until I see the benefits?
Some effects, such as lowering soil acidity, occur immediately. Other effects depend on soil biology and take time to develop. Increased cation exchange capacity will take a few years to develop fully. The good news is that these effects are very persistent.
How much improved plant growth can I expect?
You can expect that harvested weight will be, in most cases, observeably higher with a combination of char+fertilizer than you will achieve with the same amount of fertilizer alone. In some cases, the observed effect will be dramatic. Steiner (2007) reported a doubling of maize grain yield with fertilizer+char compared to fertilizer alone. Yields subsequently declined over the course of four cropping cycles, however, the decline was less with char than with without. Significantly, soil P, K, Ca, Mg remained higher in the char amended soil despite greater harvest removal.
What properties are important to the home gardener?
One of the most important quality of charcoal to the gardener is the ability to lower acidity. This is easily measured in an agricultural laboratory as calcium carbonate equivalent (CCE). Raising soil pH has been identified as biochar's most important contribution to influencing soil quality in the context of Terra Preta.
Does charcoal break down in the soil?
Charcoal is highly stable, however soil microbes do break it down, although at a very slow rate.
What is Pyrolysis?
Pyrolysis is the chemical decomposition of organic materials by heating in the absence of oxygen. This yields combustible gases (called syngas), tars and charcoal. The charcoal produced is a combination of black carbon, along with small amounts of bio-oil condensates, tars and ash.
Does Biochar affect soil pH?
Raising soil pH is biochar's most important contribution to influencing soil quality. Soil pH mostly influences the relative availability of nutrients. At low pH, aluminum toxicity is particularly harmful to plant growth. Aluminum toxicity is an extensive and severe soil problem and biochar is the most available and obvious solution that we have to combat it. Soil phosphorus availability is highly dependent on soil pH range, and thus biochar can be used to substantially increase phosphorus availability in soils that are below the ideal pH range of 6.5 to 7.0
Does Biochar affect soil biology?
The structure of the charcoal provide a refuge for small beneficial soil organisms from large grazers like earthworms. Charcoal increases activity by mycorhizal fungi. The presence of bio-char in soils actively promotes the formation of aggregates through a greater abundance of fungal hyphae. Bio-char is able to serve as a habitat for extraradical fungal hyphae that sporulate in their micropores due to lower competition from saprophytes.
How much carbon dioxide does sequestered Biochar offset?
The production of the charcoal itself has no carbon footprint assuming the fuel used to make the charcoal was diverted from fate of decomposition.
How much Nitrous Oxide formation does Biochar prevent?
Soil scientist Lucas Van Zweiten has observed a 5 to 10 fold reduction in nitrous oxide emmissions with biochars he is working with in an agricultural setting. Generally, soil with elevated soil nitrate levels in the presence of sufficient moisture and robust soil organic matter will have higher nitrous oxide production, and thus will be more likely to benefit at the levels observed by Van Zweiten.
What is the difference between Charcoal and Biochar?
Biochar and charcoal are technically two different things. The definition of Biochar (according to the International Biochar Initiative) is "a solid material obtained from the thermochemical conversion of biomass in an oxygen-limited environment." They go on to say that, “biochar can be used as a product itself or as an ingredient within a blended product, with a range of applications as an agent for soil improvement, improved resource use efficiency, remediation and/or protection against particular environmental pollution, and as an avenue for greenhouse gas (GHG) mitigation.” Charcoal is defined as "a dark or black porous carbon prepared from vegetable or animal substances (as from wood by charring in a kiln from which air is excluded)". Vegetable or animal substances.
In order to be called Biochar, it must be suitable for use in soil. Commercial charcoal is not going to necessarily be good for use in soil. Some of it may be. Some of it may not be. Many commercial charcoals are petroleum-based.
Biochar is sustainable produced, which means that it comes from waste biomass, or sustainably harvested biomass. Charcoal production is classically an unsustainable trade, and one of the biggest drivers of deforestation, particularly in developing countries.
A charcoal product is going to be optimized for its energy value. This means that factors such as fixed versus labile carbon are going to effect is market value differently than for Biochar. A high quality Biochar product should have a high fixed carbon content (meaning it will stay in the soil for a long time), minimal tars and a high surface area (giving lots of space for those little microbes).
What is the difference between Activated Charcoal and Biochar?
Activated Carbon, is dense charcoal that has been "activated" typically via a steam process or a chemical process (rather expensive). Activated charcoal is refined at higher temperatures, or acid washed to increase total surface area of the char. This drives out the volatile material (VM) fractions; tars, oils and other pyrolitic compounds.You use activated charcoal in applications where you a lot of filtration in a small space and/or the ph of the natural charcoal is a problem.