The enzyme urease is responsible for the rapid hydrolysis of urea in agroecosystems where more than 50% of the applied nitrogen (N) can be lost via ammonia volatilization. The objectives of the study were to (1) extract urease from corn (Zea mays L.) and soybean (Glycine max L.) and (2) compare the urease activity from soybean and corn residues to Jackbean (Canavalia ensiformis) urease using Fourier transform infrared spectroscopy (FTI-R). Concentrations of urea and sodium bicarbonate ranging from 0 to 200 mM were analyzed with FTI-R to determine the correlation to peak height. Bicarbonate produced the most responsive peaks to concentration at 1,362 cm −1 . Urease extracted from soybean residue was active, producing a bicarbonate peak at 1362 cm −1 , whereas no urease activity was observed in corn residue. Variation among urease activities in crop residues could suggest a need for more precise nitrogen management in conservation tillage agroecosystems to reduce ammonia volatilization.