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.

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Land-use change, particularly soil organic carbon (SOC) loss induced by shifting cultivation (jhum) is a common land degradation issue in the hilly tracts of the humid tropics. The SOC concentration comprises different pools (labile and recalcitrant fractions), and each fraction responds to temporal dynamics of adopted management practices at varying magnitudes, such as deforestation followed by cultivation. However, information on the variation of different SOC pools due to cultural practices of vegetation burning and postburn agricultural practices (crop production) associated with shifting cultivation remains inadequate. In the present investigation, we examined the effect of burning and postburning cultivation on SOC pools across different forest fallow periods at Kolasib district, Mizoram state of the north-eastern Himalayan Region of India. Results revealed increase in the soil C stocks and total organic carbon (TOC) due to the increase in the length of fallow periods ranging from 3 to 23 years. The TOC decreased significantly compared with antecedent concentrations before vegetation burning. This was mostly attributed to the reduction in contribution of active pools (very labile and labile) to TOC from 69% to 60%. However, contribution of passive pools (less labile and nonlabile) to TOC concentration increased from 31% to 40%. Postburn cultivation also resulted in reduction of TOC as well as considerable variation in the proportion of different SOC pools to TOC concentration. Among the different pools of SOC, the very labile C pool was most sensitive to land-use change induced by shifting cultivation (phytomass burning and postburn cultivation). The labile SOC pools can act as a sensitive indicator for devising suitable location specific management practices for restoration of soil health through SOC dynamics in degraded jhum lands in hilly ecosystems.

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