LONG-TERM NITROGEN FERTILIZATION EFFECTS ON CORN YIELDS AND SOIL PROPERTIES

A long-term experiment (1958-2002) provides information about the sustainability of long-term nitrogen (N) fertilizer use and continuous corn production in the northern Corn Belt. The experiment includes three N rates (none, medium, and high) applied annually in a randomized complete block design with four replications. Nitrogen rates in the medium and high categories increased over time and are currently 125 and 250 lb N/acre. Lime treatments were imposed on the long-term N rates in 1985 using a split-plot treatment arrangement. Long-term N use increased soil organic C and N content and N availability, likely due to higher residue amounts and N concentrations. Soil pH and cation exchange capacity declined without lime addition, but increased where lime was applied. Average corn yields in N fertilized treatments approximately doubled during the 45-yr history of the experiment with the highest yields occurring in the more recent years. No evidence of a decline in productivity from long-term N fertilizer use was detected