The effect of fly ash/sewage sludge mixtures and application rates on biomass production

Abstract

Abstract A greenhouse study was conducted to assess the use of a sewage sludge/fly ash mixture in soils for increased growth and uptake of nutrients by Sorghum vulgaris var. sudanense Hitchc. ("sorgrass"), a sorghum‐sudangrass hybrid plant. This experiment was conducted by using four sewage sludge‐to‐fly ash ratios (4:1, 4:2, 4:3, and 4:4) and six application rates of sewage sludge/fly ash mixtures to soil (0, 50, 100, 150, 200, and 400 tons/acre). The data in this study indicated that the availability of elements to plants varied depending on the mixture ratios and the application rates. All ratios of sewage sludge amended with fly ash generally improved plant growth and enhanced yield at application rates of 50–100 tons/acre but showed reduced growth and yield at higher application rates. The decrease in yield at higher application rates was probably due to the assimilation of high levels of boron which is phytotoxic. These various treatments of sewage sludge/fly ash ratios and rates of application often resulted in elevated concentrations of N, P, K, Ca, Mg, Mn, Fe, B, Cu, and Zn in both soil and plants.