As nitrogen (N) fertilizer prices have increased, producers have looked for ways to manage better their N programs. In addition to improving timing of applications, some growers have considered managing N differently from hybrid to hybrid. This strategy may be based on observations that N uptake patterns sometimes vary among hybrids. Also, some seed and fertilizer suppliers have occasionally promoted the concept of unique N needs and application timings for specific hybrids. This issue of variable hybrid response to N has been the focus of much field research by university and Pioneer researchers over the past 20 years.
1 Note - The hybrid difference shown in the picture is an inherent "color" difference unrelated to nitrogen fertilization. Because hybrids naturally differ in chlorophyll level, or "greenness", it is important to grow a well-fertilized calibration strip of each hybrid being tested when using a chlorophyll meter to access N needs.
The results of these studies are summarized in this article, as well as Pioneer's efforts to develop hybrids that have increased ability to utilize nitrogen.
The first key to understanding whether a hybrid x N rate interaction is occurring is a close examination of the yield response of different hybrids across a wide range in N rates. A second key is to compare only similar maturity hybrids that are adapted for the location where grown. For example, two hybrids of greatly differing maturity grown across a wide range in N rates could give the appearance of a hybrid x N rate interaction. In reality, these hybrids have very different grain and stover production potentials, and, therefore, N requirements. The third key to demonstrating whether a true hybrid x N rate interaction is occurring is to make the comparisons across numerous environments and several growing seasons. With few exceptions in past testing, hybrid x N rate interactions apparent after a single year of testing at one location disappeared when the tests were conducted over several locations and years.
Starting in the 1980s, Pioneer has conducted trials across 27 growing environments, 17 adapted hybrids and 16 growing seasons to address potential hybrid differences for nitrogen response. Nitrogen (N) rates of zero to 240 lbs/acre and N timings of all preplant, all sidedress and half preplant + half sidedress were used. The findings of these studies have consistently shown a similar response by adapted hybrids both to N rate and timing when averaged across locations and years.
Results of the most recent Pioneer studies are shown in Figure 3 and Figure 4. These response curves show the similarity of yield response to N rates among widely grown corn hybrids. Based on the extensive Pioneer data available, there appears to be no need to apply nitrogen fertilizer differently for currently grown hybrids of similar maturity.
Nitrogen X CRW Trait Research
Due to the increased use of transgenic corn rootworm (CRW) resistant hybrids, and questions around improved root development, Pioneer has examined nitrogen response for corn rootworm traits and treatments. These studies have shown that hybrids containing the Herculex® RW trait and hybrids treated with soil insecticides were not significantly different from the untreated check hybrid for nitrogen response. The benefit of the Herculex RW trait was in protecting the roots from a specific pest and not in significantly affecting the response to nitrogen.
Nitrogen strategies that suggest hybrid-specific N management face many practical limitations. It is also very difficult to document the need for "early" versus "late" N or if ammonium or nitrate-N is preferred by the crop. Regardless of the type of N fertilizer applied, most of the N taken up by corn roots is the nitrate form due to rapid nitrification (conversion of ammonium to nitrate-N in the soil). It is not feasible or necessary to manipulate the forms of N applied based on crop response.
The extensive research to date indicates that the growing environment is much more important than the hybrid in determining crop response to nitrogen rate and timing. There currently appears to be no need to manage nitrogen differently across adapted hybrids of similar maturity.
Figure 5 shows the difference in nitrogen use efficiency in a transgenic event vs. a normal hybrid. This demonstrates the impressive progress made by Pioneer researchers in the development of a more nitrogen-efficient hybrid. Growers can expect this technology to be introduced into the marketplace in the next decade.
Bundy, L.G., and P.R. Carter. 1988. Corn hybrid response to nitrogen fertilization in the northern corn belt. J. Prod. Agric. 1:99-104.
Coulter, J.A., E.D. Nafziger, R.G. Hoeft, and B.D. Young. 2004. Do Different Corn Hybrids Have Different N Needs? Poster. University of Illinois.
Gardner et al. 1990. Response of corn hybrids to nitrogen fertilizer. J. Prod. Agric. 3:39-43.
Iragavarapu, Raj. 1998. Corn Hybrid Response to Nitrogen Rate and Timing. Pioneer Crop Insights vol. 8 no. 11. Pioneer Hi-Bred, Johnston, IA.
McLeod, M. and S. Butzen. 2008. Planting Date and Nitrogen Rate Effects on Performance of Pioneer® brand Hybrids with Herculex® RW or Herculex XTRA Technologies. Pioneer Crop Insights vol. 18 no. 18.
Tsai, C.Y., D.M Huber, D.V. Glover, and H.L. Warren. 1984. Relationship of N deposition to grain yield and N response of three maize hybrids. Crop Sci. 24:277-281.
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