The use of a sewage sludge as a fertilizer for wheat in a glasshouse pot experiment

Abstract

Acid soil infertility is a major limiting factor in crop production on soils along the eastern seaboard of South Africa. Invariably this problem is addressed by effectively liming the topsoil with little influence on subsoil acidity. A study was conducted to ascertain the efficacy of sewage sludge in ameliorating subsoil acidity and providing the nutrient requirements of wheat (Triticum aestivum cv. SST66) grown under glass. Varying rates of air-dried washed sludge (0, 20, 40, 80 and 160 Mg ha⁻¹) were mixed into the top 120 mm of topsoil overlying subsoil in packed soil columns. Leachates were collected at intervals during the study period and submitted for chemical analysis. Selected soil treatments were analysed for exchangeable cations, pH and phosphorus. Significant increases in subsoil pH were only observed at the highest level of sludge application (160 Mg ha⁻¹), where pH increased from 4.4 to 5.0. With respect to leachate composition, the only two anions to leach in any significant amounts were chloride and nitrate. Sludge additions resulted in slight increases in the amounts of NH₄ ⁺ and Na⁺ in the leachates. Dry matter yields increased significantly from 1.09 g to 9.32 g with rates of application increasing from 0 to 40 Mg ha⁻¹. Higher rates of sludge application did not significantly increase dry matter yields.