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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