Agroecosystems are domesticated ecosystems intermediate between natural ecosystems and fabricated ecosystems, and occupy nearly one-third of the land areas of the earth. Chemical perturbations as a result of human activity are particularly likely in agroecosystems because of the intensity of that activity, which include nutrient inputs intended to supplement native nutrient pools and to support greater biomass production and removal. At a long-term fertility trial at Arlington, WI, significant increases in exchangeable acidity were accompanied by decreases in cation exchange capacity (CEC), base saturation, and exchangeable Ca2+ and Mg2+ with application of ammoniacal N fertilizer. Similar trends have been noticed in other long-term fertility experiments.