**5. Acknowledgements**

94 Agricultural Science

value of 0.70 and are indicative of the role of soil variation and the effect on soil water dominating the effect of N. The higher yields were found in the Webster soils as shown earlier with the frequency distribution of yields. The spatial map of yields show these high yields but the high yields are not consistent with N rates. There was the reemergence of the presence of the waterway within the field in the yield map that was present in the May spatial map of the field. These patterns within fields were found in the other fields we examined in this study and there was a significant correlation between the yield and soil type across all fields of 0.58. The growing season conditions during these study years had normal or slightly below normal precipitation amounts during the growing season and above normal precipitation during grain fill would offset these relationships and allow for more potential benefit of applied N. This finding confirms the observations from Jaynes and Colvin (1997) in which the spatial variation of yield was related to seasonal precipitation

> yield kg/ha 14573. 13959. 13344. 12730. 12116. 11502. 10888. 10273. 9659. 9045. 8431. 7817. 7202. 6588. 5974.

and extends their results to include the interacting effects of N management.

Fig. 14. Interpolated yield map from the Coon Rapids field in 2002 using spatial analysis

Nitrogen response across agricultural fields is more complex than observing a consistent response across a change in management practices. Observations among fields has shown that when multiple soils are encountered within a production field there are spatial patterns in both water use and N impacts on crop yield. There have been few studies which have coupled water and N dynamics across corn production fields. It has been assumed that water patterns operate separately from N management practices; however, the spatial patterns within a field show there is a temporal and spatial pattern determined by the combination of the precipitation patterns during the season, the soil water holding capacity, and the crop growth (crop water use) patterns. Observations of N impacts on corn yield across production scale fields revealed that yield responses were dependent upon the soil type and within a rate strip there were a range of yields and when further dissected into the

software.

**4. Conclusions** 

The support of the Risk Management Agency and especially Virginia Guzman and Dave Fulk are greatly acknowledged and this research is under the agreement 07-IA-0831-0210. This effort would not be possible without the capable support of Brooks Engelhardt, Wolf Oesterreich, and Bert Swalla in their efforts to collect and process the data from the field experiments and the interactions with Galen Hart for his encouragement and insights. Likewise, the support of the producers Don Ferguson, Mike Hermanson, Nels Leo, Kriss Lightener, Dale Pennington, and David Schroeder who willingly let us use their fields for these studies and the efforts of the Farnhamville Cooperative of Farnhamville, IA (Jeff True, Gabe Tar) for helping identify the producers. The support from CALMIT at the University of Nebraska (Rich Perk and Don Rundquist) to obtain the hyperspectral data is greatly appreciated.
