Soil Physicochemical Alteration Associated with Dolomite Influx Along the India–Bhutan Border

Dolomite, a calcium magnesium carbonate mineral, can adversely affect soil properties when present in excessive amounts. The India-Bhutan border region of West Bengal has experienced substantial declines in the quality and yield of fresh tea leaves, potentially associated with dolomite influx from the neighbouring lower Himalayas through recurrent flooding and the use of river water for irrigation. This study assessed the soil status of the affected area. The overall moisture content of the soil was low, with the lowest average values recorded in riverbeds, followed by the tea plantations. The average value of organic carbon, total nitrogen, available phosphate and potash across the study area were 1.34 ± 0.98%, 0.10 ± 0.08%, 20.27 ± 38.58 ppm and 199.18 ± 270.37 ppm, respectively. The soil pH of the study region varied from 7.85 to 3.91, with an average of 6.16 ± 1.02. The riverbeds showed average pH 6.94 ± 0.46, followed by the tea plantations (5.61 ± 0.91) and forest area (5.03 ± 0.53). The quantity of soil calcium carbonate of the area varied between 1% to 14%, with an average of 7.09%, in comparison to 0.4± 0.2% in unaffected areas. The tea plantations near the riverbeds were most affected. Elevated soil pH causes ammonia volatilization reducing the availability of nutrients such as P, N, B, Mn, Cu, Fe and Zn for the tea bushes leading to decline in productivity. Soil reclamation strategies should therefore include the potential use of calcite-solubilising microorganisms, measures to reduce further dolomite influx associated with mining activities, and appropriate hydraulic interventions, including check dams and the management of sediment accumulation in streams and riverbeds. Tea plantations should also consider avoiding river water for irrigation where it contributes to further carbonate accumulation and soil alkalinisation.