Fig. 5. Nitrogen retention in Blount and Fayette soil clays as a function of the exchangeable cation and relative humidity (RH). "Wet" samples were equilibrated at 90% RH, while "dry" were at 2% RH. Significant differences at 0.05 probability level are indicated by the different letters within the same measure: NH+4, NH3, and NH+4 + NH3.