N Transformation in Incubated Sewage Sludge and Commercial Fertilizer Enriched Soil

Abstract

Application of sewage sludge to agricultural land is an economical and effective way to dispose of sludge. There are several beneficial as well as potentially detrimental effects when sludge is applied to soils. One important aspect is the danger of nitrate (NO 3 2 ) leaching. Strict guidelines exist in South Africa concerning sludge disposal in terms of N application rates, but none for commercial fertilizer application. To evaluate the potential risk of NO 3 2 leaching from sewage sludge and commercial fertilizer, an incubation trial was carried out. The rate at which inorganic N became available from sludge and fertilizer was measured and compared. NH 4 þ concentration peaked after 7 days and NO 3 2 concentrations in the sludge treatment increased steadily up to 63 days. The rate of nitrification was initially faster in the fertilizer than in the sludge treatments, but overall, the sludge produced more NO 3 2 due to mineralization compared to commercial fertilizer. A higher risk of NO 3 2 leaching exists with commercial fertilizer over sludge applications because NO 3 2 is released continually at a slow rate from sewage sludge and rapidly from commercial fertilizer.