Monday, 7 November 2005 - 9:30 AM
42-3

In Season Crop N Management.

John Shanahan1, William Raun2, Newell Kitchen1, and Jim Schepers1. (1) USDA-ARS, 120 Keim Hall, Univ. of Nebraska, Lincoln, NE 68583-0934, (2) Oklahoma State University, 044 N. Ag. Hall, Department of Plant and Soil Sciences, Stillwater, OK 74078

Traditional nitrogen (N) management schemes for corn production in the USA have resulted in low N use efficiency (NUE), environmental contamination, and considerable public debate regarding use of N fertilizers in crop production. Hence, development of alternative schemes that improve NUE and minimize environmental impact will be crucial to sustaining corn-based farming in the USA. The major causes for low NUE of traditional N management practices are: 1) pre-plant application of large doses of N, and 2) uniform application rates to spatially variable landscapes. Pre-plant applications of high N rates results in poor synchronization between N supply and crop uptake. Uniform applications within fields discount the fact that N supplies from the soil and crop N uptake is spatially variable. When N is managed in this way it is at considerable risk for environmental loss. The use of a soil-based management zones (MZ) approach has been proposed as a means do direct variable N application rates to better match N supply with landscape spatial variation in crop N requirements. However, evidence has accumulated suggesting that the MZ approach alone will not be completely effective in making accurate variable N applications, given the large effect temporal variation in corn belt climate has on expression of spatial variation in crop N needs. Others have advocated crop-based strategies that utilize remote sensing of crop canopies to direct in-season N fertilization at a time when the crop can more efficiently utilize the N. This presentation will highlight our vision for combining the soil-based MZ and the crop-based remote sensing approaches into an integrated system for making in-season variable N applications under site-specific soil and ever-changing climatic conditions, to more efficiently apply N.

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