The net arable land area is declining worldwide rapidly due to soil erosion, drought, loss of soil organic carbon, and other forms of degradation. Intense rainfall, cultivation along steep slopes, unscientific land-use changes, shifting cultivation, soil acidity, and nutrient mining in hills and mountains make agriculture unsustainable and less profitable. Hills and mountain ecosystems of the Eastern Himalayan Region (EHR) are further prone to the impact of climate change posing a serious threat to agricultural production and the environment. Increasing soil carbon reserves contributes to multiple ecosystem services, improves soil nutrient and water-holding capacities, and advances climate-resilient agriculture. Thus, carbon sequestration is increasingly becoming an important aspect of farming among researchers in the region. The EHR predominantly practices shifting cultivation that degrades the ecosystem and promotes land degradation and biodiversity loss. Leaching of exchangeable bases is highly favored due to excess rainfall which in turn creates an acidic soil accounting for >84% of the region. Application of lime to raise the soil acidity for the cultivation of crops did not get adequate acceptance among the farming community due to multiple issues such as cost involvement, non-availability in time and place, and transportation issues. The application of biochar as soil amendments is widely known to improve soil’s physical, chemical, and biological properties. Biochar has also emerged as a potential candidate for long-term carbon sequestration due to its inbuilt structure and higher stability. Shift from traditional “slash and burn” culture to “slash and char” might lead to the sequestration of carbon from the atmosphere. Around 0.21 Pg of carbon (12% of the total anthropogenic carbon emissions by land-use change) can be sequestered in the soil if the traditional “slash and burnt” practice is converted to “slash and char”. The objective of this review is to provide detailed information about the role of biochar in altering the soil properties for sustaining agriculture and carbon sequestration, especially for hills and mountain ecosystems.

Over centuries and even today, traditional farming practices are well performed without any ecological degradation. However, management practice such as conservative tillage combined with nutrient and residue could increase the crop production as well as soil fertility. A three-year replicated study was conducted to assess the effects of agronomic modification of traditional farming practices on productivity and sustainability of rice (wet season)–rice (dry season) system (RRS). The replacement of farmers practice (T₂) with conservation effective tillage (no-till (NT)) and integrated nutrient management (INM) practice along with 30% residue retention (T₅) enhanced the straw, root and biomass yield of both wet season rice (WR), dry season rice (DR) and system as a whole over T₂. Treatment T₅ recorded significantly lower soil bulk density (ρ_b) and higher pH than the T₂ after three years of the experiment. Further, treatment T₅ increased total soil organic carbon (2.8%), total soil organic carbon stock (2.8%), carbon sequestration rate (336.5 kg ha⁻¹ year⁻¹), cumulative carbon stock (142.9%) and carbon retention efficiency (141.0%) over T₂ of 0–20 cm depth after three year. The soil microbial biomass carbon concentration was significantly the highest under T₅. Similarly, the dehydrogenase activity was the maximum under T₅. Adoption of conservation tillage and nutrient management practice involving NT and INM along with residue retention can enhance the system productivity, and C and N sequestration in paddy soils is thereby contributing to the sustainability of the RRS.