Liming is a routine crop management practice on many agricultural soils and is partly a consequence of soil acidification by nitrification of N fertilizers. The Association of Official Analytical Chemists (AOAC) in 1934 adopted soil acidification values that suggest ammonium sulfate (AS) requires three times more lime to neutralize resultant soil acidity compared to ammonium nitrate (AN) or urea. This article reports on a critical examination of the value and discusses results of laboratory and 3-year greenhouse experiments with wheat-corn-wheat-corn-wheat grown to maturity in which the liming requirement for AS compared to urea and AN was approximately 25 to 47% less than the AOAC value. This report also discusses results from field trials where soils treated with AS, urea, or AN for tall fescue growth did not significantly decrease soil pH compared to the control over a 2- to 3-year period.