Biochar Functions in Soil Depending on Feedstock and Pyrolyzation Properties with Particular Emphasis on Biological Properties

Abstract

Biochar effects are strongly dependent on its properties. Biochar improves physical soil properties by decreasing bulk density and increasing medium and large aggregates, leading to faster and deeper water infiltration and root growth. Improvement of the chemical properties of soil is connected with pH neutralization of acidic soils, increase of cation exchange capacity and base saturation, providing a larger surface for sorption of toxicants and exchange of cations. Biochar increases the stocks of macro- and micronutrients in soil and remains sufficient for decades. Biochar effects on (micro)biological properties are mainly indirect, based on the improvements of habitat conditions for organisms, deeper root growth providing available C for larger soil volume, higher crop yield leading to more residues on and in the topsoil, better and deeper soil moisture, supply of all nutrients, and better aeration. Along with positive, negative effects of biochar while used as a soil conditioner are discussed in the review: presence of PAH, excessive amounts of K, Ca and Mg, declination of soil pH. In conclusion, despite the removal of C from the biological cycle by feedstock pyrolysis, the subsequent application of biochar into soil increases fertility and improves physical and chemical properties for root and microbial growth is a good amendment for low fertility soils. Proper use of biochar leads not only to an increase in crop yield but also to effective sequestration of carbon in the soil, which is important to consider when economically assessing its production. Further research should be aimed at assessing and developing methods for increasing the sequestration potential of biochar as fertilizer.