The use of biochar for reducing carbon footprints in land-use systems: prospects and problems

Biochar, a carbonaceous solid material obtained from the pyrolysis of biomass, has received considerable research attention because of its unique properties and potential to improve crop yields and soil carbon (C) sequestration while reducing environmental degradation and carbon footprints (CF). This paper summarizes the available results on several aspects of biochar research from numerous studies despite their short-term nature. The studies have shown that (1) biochar from the same source added at a given rate to different soils could have different effects, particularly on phosphorus (P) release/retention, based on the respective soil properties; (2) the elemental composition of a feedstock (the biomass source used for biochar production) is not an indication of plant-nutrient availability; (3) pyrolysis temperature has a significant influence on the properties of the biochar, but the optimal temperature depends on the desired qualities of the product such as P release, cation exchange capacity, and surface area; and (4) the risk of nutrient loss during biochar application depends on the nutrient release potential of the biochar as well as the nutrient retention properties of the soil. Some evidence from nature suggests that biochar can hold C in soils for thousands of years, but the mechanisms involved are not fully understood. In general, the available results on the effect of biochar application on field crops have been variable and site-specific so that general conclusions cannot be drawn on their applicability to a wide spectrum of situations and systems. A number of researchable priorities were identified, including CF under biochar. Similarly, although the land application of biochar to decrease CF sounds like a promising proposition, rigorous long-term studies under farm settings are required before recommending it for large-scale adoption.