Economic assessment of desilted sediment in terms of plant nutrients equivalent: A case study in the Medak district of Andhra Pradesh. Global Theme 3: Water, Soil and Agrodiversity Management for Ecosystem Resilience Report no. 4 uri icon

abstract

  • Water harvesting, storage and reutilization for crop production is an important component of research for sustainable agricultural development in the dry regions. Traditionally in southern India, water storage tanks are an integral part of villages and the water is used for recharging groundwater and irrigating fields. Over the years, the storage capacity of tanks gets reduced due to sediment deposits from erosion and runoff processes. During 2001, the Government of Andhra Pradesh undertook the ?Neeru-Meeru? (Water and You) initiative in Medak district, for desiltation of tanks during the dry season. We assessed the viability of desilting operations and economic value of potential utilization of sediments desilted from tanks for its nutrient value. The sediment samples collected from 21 tanks spread out in 11 mandals of the Medak district were analyzed for their plant nutrient content and microbiological properties. On an average, the sediment samples contained 720 mg nitrogen (N) and 320 mg phosphorus (P) per kg of sediment. The organic carbon (C) content ofsediment varied from 5.3 g kg-1 to 27.2 g kg-1, with a mean value of 10.7 g C kg-1 of sediment. The application of 48,777 tons of sediments to agricultural lands returned 520 tons of C to fields, thereby enhancing the nutrient availability for crop production. The microbiological assays indicated that the sediment samples had higher counts of bacteria (20-30 × 104 colony forming units (CFU) g-1 of sediment) and actinomycetes followed by fungi. The benefit-cost (B/C) ratio of desilting operation and its utilization as plant nutrient source of N and P varied from 0.62 to 3.44 with an average ratio of 1.17. This suggests economic feasibility for the application of tank sediment to agricultural fields for crop production in addition to increased water storage capacity, groundwater recharge and availability of more irrigation water. The data obtained from 21 tanks was used for extrapolating results to the entire district in which a total of 78 tanks were desilted. The approach used for extrapolation utilized the N and P composition of sediments from the nearest availablesediment value to compute for rest of the tanks in the district. The overall mean N, P and organic C content in the sediments was calculated to be 730 mg kg-1 sediment, 357 mg kg-1 sediment and 11.64 g C kg-1 sediment respectively. In the district, a total of 246831 tons of sediments from 78 tanks were desilted and addition of these sediments back to farms would return 183 tons of N, 86 tons of P and 2873 tons of organic carbon. On an average, the B/C ratio for desilting operations from water tanks based on the economic plant nutrient value (N and P content) of the district was calculated to be 1.23 which reflects a positive benefit for the cost incurred in the ?Neeru-Meeru? program

publication date

  • 2003