A composition for treating waste materials such as, for example, livestock manure and mushroom compost. The composition includes: (1) gypsum obtained either as commercial product or as waste wallboard; (2) lime; (3) silica or fly ash; (4) optionally water; (5) optionally iron slag; and (6) optionally portland cement. Further provided is a method of stabilizing waste materials which includes the step of treating the waste materials with the composition. Still further provided are a method of measuring the amount of ammonia in a waste material, a method of measuring the amount of hydrogen sulfide in a waste material, or both.