AbstractInvestigations were conducted to measure the quantities of NH3 physically sorbed and the quantities of sorbed NH3 retained against evacuation by some common plant residues when exposed to NH3 in a dry condition and with different amounts of moisture. With increases in NH3 pressure both moist and dry samples of each plant residue physically sorbed increasing quantities of NH3. When saturated with NH3, evacuated, and then saturated a second time each dry plant material sorbed less NH3 during the second than during the first saturation. Increases in moisture content resulted in increases in physical sorption of NH3 across the entire range of partial pressures of NH3 employed. Saturation of the moist plant residue samples with NH3 resulted in some measurable increases in NH3 content after evacuation.