Biochar application as a negative emission technology in South Asian agriculture: a scoping review

Biochar is a carbonized biomass that is used for soil amendment. Since 60% of the population in South Asia depends on agriculture, the negative consequences of soil degradation in this region significantly impact agricultural productivity, food security, and livelihoods. While several empirical studies have been conducted on the application of biochar in agriculture, no systematic reviews have been conducted in the South Asian context, leaving an evidence gap on biochar application in agriculture. This scoping review includes a total of 26 studies published between the years 2015 and 2023 for full-text analysis and evidence synthesis. Most studies were conducted in Pakistan, followed by Nepal, Bangladesh, and Sri Lanka. However, no studies were found in Afghanistan and the Maldives. Mostly, biochar was made by using the slow pyrolysis method. Randomised Controlled Trial (RCT) was the most common method to assess the effects of biochar on soil health and agricultural productivity. The review demonstrates that application of biochar with organic manure was more effective in improving soil properties, increasing carbon sequestration, and increasing crop yield than amendments with chemical fertilizers, biochar alone, or no application of biochar. Nevertheless, soil properties and yield effects were found to vary with soil type or feedstocks used for biochar production. This review concludes that further research should focus on the long-term application of biochar, which should be done over multiple cropping seasons and crop types.