Submitted to: Farm Bureau Spokesman Press
Publication Type: Popular Publication
Publication Acceptance Date: 9/1/1999
Publication Date: N/A
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.
Technical Abstract: 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.