Crop Nutrition

Nitrogen Management for Old Versus Modern Corn Hybrids

Cristie Preston, Ph.D.

Cristie Preston

Cristie Preston, Ph.D.

Nutrien

Senior Agronomist

Agriculture has always been an integral part of Dr. Cristie Preston’s life. She grew up in southwest Virginia and had interest in crop and animal agriculture since an early age. Once she began college, she initially chose to study animal science but switched to soil science. Dr. Preston attributes her decision partly to an influential professor who told her, “You can’t understand animals until you understand what they eat.” She received a Bachelor of Science degree in animal science and a Master of Science degree in crop and soil environmental science from Virginia Tech. Dr. Preston holds a Ph.D. in agronomy, focusing on soil fertility from Kansas State University. While completing her advanced degrees, Dr. Preston conducted more than six years of field and lab research. Dr. Preston has experience in laboratory research measuring volatility loss from urea-based fertilizers. Her field research has focused on phosphorus availability and the interactions with tillage and placement. She also has extensive experience in working with large data sets and analysis. Her main priority is helping growers to identify yield-limiting factors and fix those issues as cost efficiently as possible.

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Corn yield increases over the past 60 years can be attributed to a myriad of different factors — improved hybrid genetics (including transgenic events), better nutrient management, improved pest management, and improved agronomics practices. As corn grain yields continue to rise, because of these factors, how has nitrogen utilization changed? Or has it? If it has changed, what do these changes affect?

Corn hybrid yield and N uptake

The evolution of genetics has allowed for substantial average yield increases in the U. S. (Figure 1). Since 1960, corn yields have risen at a rate of 0.9 bushel per acre per year.

Figure 1. U.S. average corn yield, 1960-2017 (USDA)
Figure 1. U.S. average corn yield, 1960-2017 (USDA)

Dr. Tony Vyn, Professor of Agronomy at Purdue University, has conducted research and collected data on old and modern age corn hybrids extensively in Indiana, in order to update nitrogen management strategies.

Vyn has defined the “old era” hybrids as those researched between 1940 and 1990 and “new hybrids” from 1991 to 2011 (Ciampitti and Vyn, 2014). Greater stress tolerance to nitrogen deficiency and responsiveness to nitrogen rate was observed in modern corn hybrids.

In some of his more recent research (Vyn et al., 2016), both grain yield and plant nitrogen uptake of modern hybrids were higher than older hybrids. Modern hybrid average yields were 240 bushels per acre versus an average of 200 bushels for older hybrids. However, the hybrids being used today are even newer than those in the study above, which begs the question: will there be an even newer hybrid group yield from 2011 to 2016.

When comparing the old and new hybrids, as nitrogen application rate increased, yield also increased with both old and new hybrids (Figure 2). When no nitrogen fertilizer was applied (zero pounds N per acre), new hybrids yielded on average 13 bushels more per acre compared to older hybrids. As application rate increased, so did the gap between old versus new corn hybrids. At the highest rate, above 250 pounds of nitrogen per acre, the yield gap between old and modern hybrids was increased to 32 bushels per acre (on average).

Figure 2: Corn grain versus overall
Figure 2. Corn grain versus overall fertilizer N rate applied (adapted from Ciampitti and Vyn, 2014)

His research has also revealed a change in corn nitrogen internal efficiency (expressed in bushels per pound of N taken up). Over time, nitrogen concentrations in grain have decreased by roughly 10 percent when comparing old versus modern hybrids. This is likely the result of selection of higher-yielding genetics that transport more photosynthate to the grain (starch) diluting the protein content (nitrogen concentration).

Both older and new hybrids have had similar Nitrogen Recovery Efficiency (NRE) — [((nitrogen uptake with fertilizer – nitrogen uptake without fertilizer)/ nitrogen rate)] — with an overall average of 0.46. Reduction in NRE increases both environmental risk of N loss and lower farmers’ profitability. Therefore, there are no major differences here for old versus new hybrids.

Figure 3: Higher and later N uptake
Figure 3. Higher and later N uptake in modern corn hybrids (adapted from Mueller and Vyn, 2016)

Addressing Nitrogen Recommendations

Dr. Robert Mullen, Director of Agronomy at Nutrien, previously worked on nitrogen recommendations at The Ohio State University. He found that, over time, corn production efficiency has increased. Corn plants are now capable of producing more bushels per pound of nitrogen applied — nitrogen use efficiency (NUE) or, in other words, a decrease in pounds of nitrogen required to produce one bushel — nitrogen internal efficiency (NIE).

Historically, we have utilized yield goal to determine nitrogen application rates. However, does yield level actually correlate with the amount of nitrogen required to achieve that yield level? The answer is no, achievable yield is not well correlated with amount of nitrogen required to get there.

Even though Vyn’s research doesn’t show any changes in the mean nitrogen rate applied (Table 1), the Nitrogen Use Efficiency (NUE) has increased with modern hybrids. Thus, changes to the nitrogen recommendations may result in higher yield.

Table 1: Summary of variable compared for old and new era corn hybrids (Ciampitti and Vyn, 2014).
Table 1. Summary of variable compared for old and new era corn hybrids (Ciampitti and Vyn, 2014)

The other major thing to note is that any improvement in corn production can be achieved by removing a limiting factor (i.e. drought tolerance, pest management improvement, etc.). Removing any of these limiting factors (see an eKonomics™ article on Liebigs Law) improved production, but does not necessarily affect nitrogen response.

How else to increase your NUE? Reduce chances of losses by considering the 4R approach (right source, right time, right place, right rate) to nitrogen management.

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