Long-Term Continuous Corn and Nitrogen Fertilizer Effects On Productivity and Soil Properties.

There are uncertainties about the sustainability of long-term monoculture and nitrogen (N) fertilizer use in corn production.  Long-term research (50 years) at the Arlington Agricultural Research Station has examined the effects of continuous corn and N fertilizer use on corn yield, N use efficiency, and soil characteristics.  Corn was harvested for grain with residues returned annually since 1958 on a Plano silt loam soil (fine-silty, mixed mesic, Typic Argiudolls).  The experimental design includes three N fertilizer rates (currently, 0, 140 and 280 kg N ha^-1) and two lime treatments (imposed in 1985) with four replications.  Soil pH and organic matter content were measured periodically during the experiment.  Average corn yields in N fertilized treatments increased dramatically (100%) over time with some of the highest yields occurring in the most recent years.  Nitrogen use efficiency (grain N/fertilizer N) also increased over time, thus higher yields in recent years have not required greater N fertilizer use.  Soil organic matter content was at least maintained and, in some cases, increased with long-term N additions, thereby enhancing the soil N supply capability.  Soil pH decreased with long-term N use without lime addition, and since 1987, lime treatments increased yields in 13 of 21 years.  Increasing productivity and N use efficiency along with no reduction in soil organic matter suggest that long-term continuous corn and N fertilizer use are sustainable practices in southern Wisconsin.