A 400-ha subbasin study within the Walnut Creek watershed near Ames, IA, confirmed that using late-spring soil nitrate nitrogen (NO3–N) test (LSNT) fertilizer recommendations could significantly reduce NO3–N loss in drainage water, but detailed crop response was not reported. Herein we summarize corn (Zea mays L.) response to the LSNT program when implemented across the Clarion–Nicollet–Webster soil association. The LSNT was used to determine the recommended N fertilizer rate that was applied uniformly across each field except on check strips where zero or nonlimiting (>220 kg N ha−1) sidedress N was applied. Leaf chlorophyll (SPAD) readings, end-of-season stalk nitrate concentrations, and grain yield and quality (protein, starch, and oil content) showed significant year, field, soil map unit and N rate response. Average grain yield with the LSNT program was significantly lower than the nonlimiting rate in 1997 and 1998 but not in 1999 or 2000. This suggests that although watershed-scale implementation of the LSNT can reduce nitrate loss through drainage water, it may also increase producer risk, especially when above-normal rainfall occurs shortly after the sidedress N fertilizer is applied. To encourage adoption of the LSNT program for its water quality benefits, we suggest that federal, state, or private agencies develop affordable risk insurance or some other financial incentives to help producers minimize the potential crop risk associated with this program.
Available at: http://works.bepress.com/douglas_karlen/22/