Nitrogen Availability from Sewage Sludge1
- F. R. Magdoff and
- J. F. Amadon2
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 NO3-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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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