EFFECTS OF LONG-TERM SOIL ACIDIFICATION DUE TO NITROGEN-FERTILIZER INPUTS IN WISCONSIN

Agroecosystems are domesticated ecosystems intermediate between natura l ecosystems and fabricated ecosystems, and occupy nearly one-third of the land areas of the earth. Chemical perturbations as a result of hu man 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 produc tion and removal. At a long-term fertility trial in South-Central Wisc onsin, USA, significant increases in exchangeable acidity were accompa nied by decreases in cation exchange capacity (CEC), base saturation, and exchangeable Ca2+ and Mg2+ with application of ammoniacal N fertil izer. Plant analysis shows that a considerable portion of the alkalini ty generated by assimilation of N (and to a lesser extent by S) is seq uestered in the above-ground plant parts as organic anions and is not returned to the soil if harvested. Elemental analysis of Ca-saturated soil clays indicates an loss of 16% of the CEC of the soil clay and mi nor increases in Fe and Al. The reversibility of these changes due to prolonged acidification is doubtful if the changes are due to soil wea thering.