Adjusted T values for conservation planning in Northwest Himalayas of India

ABSTRACT:

Tolerable soil loss (T) is defined as the maximum rate of annual soil erosion that economically and indefinitely will continue to sustain a high level of crop productivity. Currently a T value is assigned to a soil based on its current functional state and structural integrity. However, in India a default T value of 11.2 Mg ha⁻¹ yr⁻¹ (5.0 t ac⁻¹ yr⁻¹) is being followed. Our objective is to provide adjusted T values for India's Northwest Himalayan region by incorporating bulk density, water stable aggregate measurements, infiltration rate, soil carbon, and fertility status into the assessment. A quantitative model was used to sum up overall soil performance to define the current state of soil resource. Scaling functions were used to convert soil parameters to a 0 to 1 scale. The normalized values were then multiplied by appropriate weighting factors based on relative importance and sensitivity analysis of each indicator. A categorical ranking of soil 1, 2, or 3 was given to a soil group based on the overall assessment. A general guideline developed by the USDA-Natural Resources Conservation Service (NRCS) was followed to calculate soil loss tolerance for each soil group using effective soil depth. Adjusted T values for the area ranged between 5.0 and 12.5 Mg ha⁻¹ yr⁻¹ (2.2 and 5.6 t ac⁻¹ yr⁻¹) compared to 11.2 Mg ha⁻¹ yr⁻¹ (5.0 t ac⁻¹ yr⁻¹). Use of the adjusted T values will improve conservation planning, help meet erosion control regulations for development of sustainable farm operations, and improve watershed management in this portion of India.