Submitted to: Farm Bureau Spokesman Press
Publication Type: Popular Publication
Publication Acceptance Date: September 1, 1999
Publication Date: September 1, 1999
Citation: Dinnes, D.L., Jaynes, D.B., Cambardella, C.A., Colvin, T.S., Hatfield, J.L., Karlen, D.L. 1999. Split application nitrogen fertilizer management effects on corn yield and water quality. Farm Bureau Spokesman Press. 1999 Autumn Harvest Issue. Iowa Farm Bureau, West Des Moines, Iowa.
Media headlines have put the issue of agriculture's nitrogen (N) fertilizer use and its impact on water quality at the forefront of environmental concerns for the U.S. The Walnut Creek N Initiative was undertaken to address nitrate contamination of surface waters from tile drained fields at the watershed scale. The project's goal is to determine if the adoption of fthe late-spring nitrate test (LSNT) as an N fertilizer management tool has the potential to reduce N contamination of surface waters at the watershed scale without compromising farm profitability. Beginning in 1997, we implemented the LSNT N management program on a 1000 acre subbasin of the Walnut Creek Watershed. The LSNT method is designed to increase N fertilizer use efficiency through improved timing of N fertilizer application and estimating required N fertilizer rates by sampling soil for plant-available N in early June. Precision farming technologies are being used to measure crop yields and to aid economic analyses. Stream monitoring stations have been established at an adjacent conventional N management subbasin to serve as a control to compare against the LSNT N management system. Corn yields of the LSNT program in 1997 were on average within 99% of that from nonlimiting N strips, but only within 89% of that from nonlimiting N strips in 1998. Analyses of 1997 data revealed that both subbasins had similar nitrate-N concentrations. In late March 1998, the nitrate-N concentration trend for the LSNT split application subbasin began to diverge from the conventional N management subbasin. Since mid-September 1998, the LSNT split application subbasin has maintained a substantially lower nitrate-N concentration than the conventional N management subbasin, which analyses indicate is a significant reduction.