Economic evaluation of sediments as a source of plant nutrients

Abstract

Sediment deposition as a result of soil erosion is a significant problem in the village water tanks. In order to increase the rainwater storage capacity, removal of sediments from water tanks was taken up under the State Government Water Conservation Programme in Medak District, Andhra Pradesh, India. The feasibility of desilting operations and returning such huge amounts of sediments to agricultural fields was assessed by determining the sediment quality in terms of nutrients, organic carbon (C), biological properties and their economic value as a source of plant nutrients. Analysis of sediment samples showed an average of 720 mg nitrogen (N), 320 mg phosphorus (P), 310 mg potassium (K) and 9.1 g of organic C per kg of sediment. Higher microbial populations were found in the sediments that recorded high nutrient and organic C contents. The microbial biomass C in the sediments recorded an average value of 308 mg kg–1 sediment and the average proportion of microbial biomass C to organic C was 3.8%. Application of 48,777 t of sediment from 21 tanks returned 34 t of N, 15 t of P, 15 t of K and 433 t of organic C to agricultural lands. The benefit– cost ratio of desilting operation and application of sediments to agricultural lands in 21 tanks varied from 0.65 to 5.38, with an average ratio of 1.88. Further, extrapolation of the results for the N, P, K and organic C nutrient values to 78 water tanks in Medak district indicated that 177 t of N, 82 t of P, 76 t of K and 2016 t of organic C could be returned to the agricultural fields. The study suggests economic feasibility for the application of tank sediments to the agricultural fields for crop production, in addition to increased water storage capacity, groundwater recharge and availability of more irrigation water and environmental benefits