The kinetics of axed ammonium release from plough layer of manured loessial soil (expressed as S₁₁,)and the soil where organic matter (OM.)was destroyed by oxidation (as S₁₂) in Shaanxi Province of China were investigated using aerobic incubation-intermittent leaching method.The incubation was lasted up to 20 weeks to reach the maximum NH₄⁺ release.The kinetics of fixed NH₄⁺ release were evaluated using the Elovich,parabolic diffusion law,first-order diffusion and zero-order equations.The first-order equation described the NH₄⁺-elease kinetics best as evidenced by the highest correlation coefficient (r) and the lowest valise of the standard error of the estimate (SE).The parabolic diffusion law also described the data satisfactorily,indicating that fixed NH₄⁺ release was a diffusion-controlled process.Although the Elovich equation was also suitable to fit the NH₄⁺-release,the zero-order one was not as good as above ones,as shown by higher SE values than those found with the other equations.fixed NH₄⁺-release rate coefficient (k_r) was 0.1097/week and 0.08834/week,and maximum NH₄⁺-release amount 98.42mgN/kg soil and 85.25mgN/kg soil as well as the half time values of NH₄⁺-release (t_1/2)6.32 weeks and 7.85 weeks for S₁₁ and S₁₂ respectively.Both nitrification and soil organic matter affected fixed-NH₄⁺ release.