Greening with black Biochar-soil amendment for low-emission agriculture

Climate change is arguably the world’s greatest threat of the 21^st century and agriculture is both a contributor and victim. Biochar (pyrogenic organic matter) has emerged as an innovative way to sequester soil carbon and reduce emission of greenhouse gasses while improving soil fertility fom crop production. However, several questions remain as to the mechanisms responsible for biochar’s effect, and whether practical benefits for farmers are achievable under field conditions on low-fertility tropical soils. A combination of laboratory, greenhouse and field experiments showed that (i) surface chemistry of biochar (as affected by feedstock, pyrolysis temperature and steam activation) plays a significant role as a mechanism in GHG regulation by biochar (ii) biochar reduces emissions of both NH₃ and N₂O by ~55%, but the reduction was not linked to N dynamics (iii) as indicated by the mean weight diameter (MWD) of soil MWD), aggregate size distribution was not affected by biochar alone, but increased when in combination with either T. diversifolia (BT) or urea (BU), suggesting that biochar can affect the physical condition of soil, which in turn affects GHG emissions (iv) by reducing emissions intensity while increasing crop yield, biochar provides practical benefits to farmers in low fertility tropical soils (v) biochar’s residual effects under field conditions persist for more than three years. From these studies, it appears that the net effect of biochar on emission of these gasses is a non-additive contribution of the various mechanisms acting concurrently in the soil system. These GHG reduction mechanisms can translate into practical realities in the field and can benefit farmers through soil carbon build-up and crop yield improvement. It is recommended to undertake long-term multi-location field trials involving a wide range of biochar and soil properties to improve accuracy of the estimated effects of biochar on various agronomic and environmental benefits. The economics of biochar production from a wide range of feedstock and its inclusion in global carbon markets remains an important area for further investigation.