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Interpretive Summaries:
Improving Nitrogen Fertilization of Manured Fields in Kansas, 2009
The appropriate application rate of inorganic N fertilizer for manure-amended fields is sometimes difficult to determine for several reasons. The goals of this study were to determine N response of winter wheat on manure-amended soil, evaluate N availability calculations recommended by Kansas State University (KSU), and examine application of optical sensors for making in-season N recommendations. Field experiments were conducted at three sites (Blaine, Manhattan, and Hays) during the 2008-2009 winter wheat growing season. Whole plot treatments were pre-plant N source (manure or fertilizer) and sub-plot treatments were in-season top-dress N rates (urea ammonium nitrate at 0 to 80 lb N/A). A reference treatment of 120 lb N/A was also applied at planting. A GreenSeeker RT 200 (Ntech Industries, Inc., Ukiah, California) was used to measure normalized difference vegetation index (NDVI) in winter wheat on whole-plot treatments.
At all three sites, there was no interaction between pre-plant N source and top-dress N rate, indicating that both manure and fertilizer treatments responded similarly to top-dressed N application. Results of the evaluation of in-season N recommendation tools showed that KSU recommendations performed well at the Blaine site and the Greenseeker performed well at the Manhattan site, but neither recommendation tool performed well at the Hays site. This suggests that both the KSU and GreenSeeker methods have the potential to produce appropriate recommendations on manure-amended fields, but more work is needed for further clarity. This project was supported with in-kind soil and plant analysis FAR contributions, and further support will be evaluated on a year-to-year basis. KS-39F
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