|Hurburgh, Charles - IOWA STATE UNIVERSITY|
|Rippke, Glen - IOWA STATE UNIVERSITY|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 9, 2005
Publication Date: June 6, 2005
Citation: Karlen, D.L., Dinnes, D.L., Jaynes, D.B., Hurburgh, C.R., Cambardella, C.A., Colvin, T.S., Rippke, G.R. 2005. Corn response to late-spring nitrogen management in the Walnut Creek watershed. Agronomy Journal. 97:1054-1061. Interpretive Summary: Nitrogen fertilizer management practices need to be improved to reduce losses of soluble nitrogen to surface and water resources. To provide producers with the information needed to encourage them to adopt the new management practices, research must be conducted at a scale that is consistent with their production practices. We demonstrated that plant chlorophyll and end-of-season stalk nitrate concentrations can be useful indicators for evaluating nitrogen (N)response at the field and watershed scale. Managing nitrogen fertilizer applications for corn production in central Iowa using the late spring nitrate test (LSNT) provided enough nitrogen to meet plant requirements, except in 1998, when above normal rainfall occurred for several weeks immediately after the fertilizer was applied. We conclude that using the LSNT fertilizer management program within an entire watershed did not result in an unacceptable amount of nitrogen deficient corn or reduced grain production. These results are important for producers, crop consultants, extension agents, and regulatory personnel because they demonstrate that corn can be produced with less nitrogen loss than is associated with current management practices.
Technical Abstract: The late-spring soil nitrate nitrogen (NO3-N) test (LSNT) and end-of-season cornstalk NO3-N test have been suggested as tools for improving nitrogen (N) management but have not been evaluated at the watershed scale. Our objective was to quantify the crop productivity impact of using the LSNT to determine N fertilizer rates for corn (Zea mays L.) grown on the Clarion-Webster-Nicollet soil association within the Walnut Creek watershed in central Iowa. Leaf chlorophyll (SPAD) readings, end-of-season stalk NO3 concentrations, grain yield and quality (protein, starch and oil content) were evaluated for three N fertilizer treatments (~50 kg N ha-1, LSNT-based N fertilization, and non-limiting >220 kg N ha-1) for four years. All four indicators showed significant year, field, and soil map unit differences. The LSNT program provided an adequate amount of N to meet plant requirements, except in 1998 when above normal rainfall occurred for several weeks immediately after the side-dress N fertilizer was applied. End-of-season stalk NO3 concentrations averaged 1.4, 0.4, 1.7, and 2.7 g N kg-1 in 1997, 1998, 1999, and 2000, respectively. SPAD readings averaged 50, 45, 51, and 54, respectively. Both were sensitive indicators for monitoring N response. Grain protein tended to decrease throughout the study except when water was limiting. We conclude that using a LSNT fertilizer management program within an entire watershed did not result in an unacceptable amount of N deficient corn or reduced grain production, and therefore, we support its adoption as a management practice that can reduce N loss from tile-drained watersheds.