The Thermal Release of Ammonium Nitrogen from Ammonium Chloride‐Treated and Nontreated Soils

Comparisons were made of the thermal release of NH 4 + ‐N from soils and NH 4 + ‐saturated soils. Fixed NH 4 + ‐N was lost from untreated and NH 4 Cl‐treated soil samples when the samples were subjected to temperatures above 400C. A treatment of 800C for 5 min generally released more than 85% of the fixed NH 4 + ‐N. However, small amounts of indigenous fixed NH 4 + ‐N, 25 to 30 ppm N, may be retained by some soils when they were subjected to a temperature treatment of 1,000C for 5 min. Release of exchangeable NH 4 + ‐N was essentially completed when samples were subjected to a treatment of 500C for 5 min. The nontreated surface soils exhibited sharp increases, three‐ to sixfold, in their exchangeable NH 4 + ‐N when samples were heated at 250 or 300C for 5 min. It is suggested that these increases were derived from NH 4 + ‐N being released as soil organic matter decomposed.