Finding a balance
By Treena Hein
The trial studied research sites consisting of 12 hybrids at five rates of nitrogen and three fungicide treatments, all replicated four times. Photo by Dave Hooker
Various traits found in modern corn hybrids have an impact on the nitrogen rate that is best applied to maximize yield, the nitrogen (protein) content in the grain, and the amount of residual nitrogen remaining in the soil following harvest. But how great is this impact?
University of Guelph professors Dr. David Hooker (of the Ridgetown Campus department of plant agriculture) and Dr. John Lauzon (of the school of environmental sciences) have delved into this question and have new information to share.
“Nitrogen (N) use efficiency gives an indication of the apparent recovery of fertilizer N in the grain,” Hooker explains. “Finding out how efficient a hybrid is in the uptake of nitrogen may not only lead to determining whether it’s feasible to target hybrid-specific nitrogen rates, but to adjust nitrogen rates by hybrid according to the intended market destination.” For example, hybrids with low grain nitrogen content would be suited for ethanol production, and those with higher grain nitrogen (protein) would be better suited for livestock feed.
The study involved three sites – Ridgetown, West Lorne and Exeter – in 2010 and three again – Ridgetown, West Lorne and Belmont – in 2011. All treatments were replicated four times at each site, for a total of 720 plots per site. The treatments included five fertilizer nitrogen rates, six pairs of corn hybrids (single trait Roundup Ready isoline versus triple-stacked Roundup Ready, corn borer and rootworm resistant, and varying degrees of disease tolerance), and three fungicide treatments (untreated, Headline, Proline). This project was funded by the Ontario Farm Innovation Program through the Agricultural Adaption Council, Grain Farmers of Ontario, several seed corn companies, Bayer CropScience and BASF.
The most economic rate of nitrogen application depended on the hybrid. In all cases in both years, as expected, grain yield increased with increasing fertilizer N rate. However, some hybrids tended to respond more (in yield and economically) to additional N, up to the highest rate of N applied. With other hybrids, maximum economic yield was reached at lower N rates. The amount of nitrogen or protein in the grain also depended on the level of N fertilizer and hybrid.
“Generally, the grain N content followed a similar trend to that of grain yield in specific hybrids,” Hooker notes. “In other words, hybrids that responded the most to nitrogen in yield also had the highest nitrogen content in the grain. In general, in most hybrid lines, the stacked trait version had greater N uptake than just the Roundup Ready version.”
There was little evidence to show an improvement in N use efficiency or plant growth with the fungicides or with the stacked traits (Bt corn borer + Bt corn rootworm) over the glyphosate tolerant version of hybrids. “This could be related to the lack of disease and insect pressure in the study,” Hooker explains. “These results are in contrast to other studies in the United States that show hybrids with the Bt-corn rootworm trait characterized with higher yields and response to nitrogen compared to its non-Bt glyphosate-tolerant isoline.”
However, unlike those fields in the United States, none of the fields in this study were planted corn after corn, and disease pressure was relatively low. Both insect and disease pressure can reduce nitrogen uptake because grain yield potential may be more limited. In other words, if diseases are controlled with a fungicide application, or if insects are controlled using Bt proteins, Hooker says, nitrogen uptake may be greater because of a higher yield potential.
“However, grain yield was highly dependent on the choice of hybrid, with some hybrids characterized by a greater nitrogen use efficiency, or response to fertilizer nitrogen, more than others,” he says. “Some hybrids tested were consistent across field locations, while others responded variably to nitrogen application.”
Overall, the differences in fertilizer nitrogen use efficiency were largely a function of yield, with higher-yielding hybrids tending to have greater efficiency than low-yielding ones. However, because of the way N use efficiency is calculated, high fertilizer use efficiency can also be a result of low yields with no fertilizer N and normal yields with fertilizer N applied.
“High crop yield potentials generally have higher N use efficiency at a given N application rate,” Hooker says. “However, equally important were the yields in plots receiving no N, since check yield is part of the calculation for N use efficiency of all the other N rates. The hybrids most responsive to nitrogen (and the high yields) tended to be the ones with the lowest yields if nitrogen rate was lower than optimal.”
In summary, this project showed tremendous differences among hybrids in response to fertilizer nitrogen. “The results have significant implications moving forward,” Hooker says. “Other studies I’ve done have shown differences in hybrids with a fungicide application even though disease pressure may be low. The same studies also show synergistic effects between nitrogen rate, fungicide application and plant population, but most intriguing: the responses were highly dependent on hybrid.”
From 2012 to 2014, Hooker continued the studies, including plant population variables in addition to hybrid/N/fungicide effects (look for study results in an upcoming issue of Top Crop Manager). Starting this year, he and his team are looking at site-specific variables into the responses as well. Hooker adds that the Ontario Corn Committee is proposing to factor management levels into their hybrid testing for generating hybrid-specific management information to industry and growers.
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