Eco-restoration of coal mine spoil: biochar application and carbon sequestration for achieving UN sustainable development goals 13 and 15.
Open cast coal mining causes complete loss of carbon sink due to the destruction of vegetation and soil structure. In order to offset the destruction and to increase sequestration of carbon, afforestation is widely used to restore these mine spoils. The current field study was conducted to assess the ecosystem status, soil quality and C pool in an 8 years old reclaimed mine spoil (RMS), compared to a reference forest (RF) site and unamended mine spoil (UMS). Biochar (BC) prepared from invasive weed Calotropis procera was applied in this 8 year RMS at 30 t ha-1 (BC30) and 60 t ha-1 (BC60) to study its impact on RMS properties and C pool. Carbon fractionation was also conducted to estimate inorganic, coal and biogenic carbon pools. The C stock of 8 year old RMS was 30.98 Mg C ha-1 and sequestered 113.69 Mg C ha-1 CO2. BC30 and BC60 improved the C-stock of RMS by 31% and 45%, respectively, and increased the recalcitrant carbon by 65% (BC30) and 67% (BC60). Spoil physio-chemical properties such as pH, cation exchange capacity, moisture content and bulk density were improved by biochar application. The total soil carbon at BC30 (36.3 g C kg-1) and BC60 (40 g C kg-1) was found to be significantly high compared to RMS (21 g C kg-1) and comparable to RF (33 g C kg-1). Thus, eco-restoration of coal mine spoil and biochar application can be effective tools for coal mine reclamation and can help in achieving the UN sustainable development goal 13 (climate action) by increasing carbon sequestration and 15 (biodiversity protection) by promoting ecosystem development.