Nitrogen Availability from Sewage Sludge

Abstract

Abstract Aerobically treated secondary liquid sewage sludge was applied to both corn ( Zea mays L.) and hay growing on Hadley sandy loam and Nellis loam soils. The nine treatments consisted of a check, four ammonium nitrate levels (50, 100, 150, and 200 kg N ha −1 yr −1 ), and four sludge levels (chosen to supply amounts of available N similar to the ammonium nitrate rates). About 54% of the organic‐N added to the sludge‐amended corn soils was mineralized under laboratory conditions. The amount of N mineralized was well correlated with a chemical test of N availability. While the corn and hay on the sludge‐amended Hadley soil out‐yielded the N treatments, nitrate recovery to 1.2 m in the corn plots indicated that the available N supplied by the sludge treatments was no greater than that supplied by ammonium nitrate. Other factors, such as increased K supply to both corn and hay and residual N effect on the second‐year hay, probably caused the increased response of crops to sludge over N. There was little or no response of corn yields to sludge or N on the Nellis loam, while the hay responded more to N than sludge. Estimates of mineralization of organic‐N from sludge applied to corn and hay averaged 55% for the first year of applications. Recovery of N in the corn at harvest plus soil NO 3 ‐N to a depth of 1.2 m was positively correlated with the estimated mineralization of organic‐N (from the N availability test) plus the inorganic‐N added. The autoclaving test of N availability appears useful in predicting mineralization of organic‐N from sludge under field conditions.