Biochar has been touted as a soil amendment that can improve crop yields up to 400 per cent, mitigate global climate change by sequestering carbon dioxide and enhance the ability of soil to hold water and nutrients. All of this is true . . . to a point. The dramatic results have been found by studies that sometimes apply more than 10 tonnes of biochar per hectare. Fortunately, some of these positive effects can also be found at lower application rate.
Scientists have identified a “complex, nutrient-rich organic coating on co- composted biochar,” according to Hagemann et al (2017). This coating is largely responsible for the ability of biochar to retain nutrients.
To maximize the benefits of biochar, the key is to compost the biochar with manure or other compost feedstocks (materials) with a high nutrient content. This will “enhance the agronomic performance of biochar as a soil amendment” and may lead to higher crop yields at a moderate application rate of 0.5-2 tonnes of biochar per hectare.
Source: Organic coating on biochar explains its nutrient retention and stimulation of soil fertility. Nikolas Hagemann, Stephen Joseph, Hans-Peter Schmidt et al., Nature Communications, 2017; Volume 8, Number 1089, pp. 1-11.
- Janet Wallace