Why use biochar in agriculture?
The growth of agricultural crops generally increases when biochar is introduced. The positive effects become more pronounced as the biochar supplement is increased, up to around 20 per cent biochar. The greatest effect is obtained in acidic and sandy soils. In Swedish experiments, growth increases of up to 33 per cent have been observed when introducing 2 per cent biochar per square metre of soil.
However, there are also experiments where the addition of biochar has not produced any positive effects on growth, and even those that have resulted in reduced growth. This may be because the microbial activity increases when biochar is added, which can lead to an initial nutritional deficiency for the crops, especially when it comes to nitrogen. Nitrogen may therefore need to be added along with the biochar. Nitrogen fertilisation in combination with the addition of biochar has in many cases been shown to lead to more efficient uptake of nitrogen in the crops.
There are currently relatively few studies that have evaluated the long-term effects of biochar and its repeated use on agricultural crops.