Hybrid Response to Nitrogen Fertilizer: Are There Differences?

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By Greg Luce and Jeff Mathesius

Summary

Pioneer has conducted extensive nitrogen x hybrid studies since the 1980s and has not found significant differences in hybrid response to nitrogen.
Recent Pioneer research has shown that current corn hybrid differences in nitrogen utilization are small and do not require different nitrogen recommendations.
Numerous university studies have examined hybrid response to nitrogen and have not shown consistent differences from season to season when comparing adapted hybrids of similar maturity.
Pioneer has an extensive research effort that is focused on identifying transgenic events in corn that can utilize nitrogen more efficiently.

Introduction

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.

Do corn hybrids require different rates of nitrogen fertilizer?¹

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.

What is a Hybrid x Nitrogen Rate Interaction?

A hybrid x N rate interaction means that the grain yields of two hybrids respond differently across a range of N application rates. This theoretical interaction is depicted in Figure 1 and Figure 2.

Response of two hypothetical corn hybrids across a range of N application rates. A large difference between the optimum N rates for the two hybrids. — **Figure 1.** Response of two hypothetical corn hybrids across a range of N application rates. Note the large difference between the optimum N rates for the two hybrids.

Response of two hypothetical corn hybrids across a range of N application rates. No difference in the optimum N rate for the two hybrids. — **Figure 2.** Response of two hypothetical corn hybrids across a range of N application rates. Note there is no difference in the optimum N rate for the two hybrids.

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.

Pioneer Nitrogen x Hybrid Studies

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.

**Figure 3.** Grain yield response of three corn hybrids to N application rate. 8 environments, 2004.

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.

University Research

Many University studies have compared hybrids for response to nitrogen. Research conducted in the 1980s at Purdue University indicated that some differences may exist. However, this work compared hybrids that varied greatly in comparative relative maturity. Hybrids that vary greatly in maturity tend to have large yield differences and lower yielding hybrids tend to plateau with somewhat lower rates of nitrogen. Subsequent multi-year studies conducted by scientists at the University of Wisconsin and the University of Illinois found no consistent evidence for hybrid x N rate interactions in numerous adapted hybrids.

A recent university study conducted by the University of Illinois found that economically optimal N rate values varied somewhat among hybrids within a given year, but inconsistently in consecutive years. Similar to the research by Pioneer and other universities, this study showed that there was not a consistent N x hybrid response from year to year.

**Figure 4.** Grain yield response of four corn hybrids to N application rate. 6 environments, 1993-94.

Conclusions from Nitrogen x Hybrid Research

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.

Nitrogen-Efficient Hybrids from Pioneer

Pioneer Hi-Bred is focused on the development of improved nitrogen use efficiency in corn hybrids. Pioneer researchers are currently using biotech and conventional approaches to develop corn hybrids that are more responsive to applied N.

Transgenic event in early August compared to non-transgenic control in corn field. — **Figure 5. Right:** Transgenic event in early August. **Left:** non-transgenic control.

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.

References

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.