Bt Ups Nutrient Needs

Corn hybrids containing the Bt trait for corn rootworm resistance appear to have greater fertility needs. Research by University of Illinois corn physiologist Fred Below confirms it is important for corn growers to reconsider fertility programs when using this trait technology in order to reach the yield potential of the hybrid.

Below said the objective of his studies was to determine how modern, transgenic insect-protected corn hybrids in high-yielding systems take up and use nutrients. Below's research group conducted two studies in the Champaign, Ill., area in 2008, 2009, and 2010 and in the DeKalb, Ill., area in 2009 and 2010. They used six hybrids ranging in relative maturity from 111 to 114 days carrying genetic resistance to feeding from western corn rootworm and European corn borer.

The project was partially funded by Monsanto, a major seed and trait provider, and Mosaic, a fertilizer company. The research measured corn yield and how much of each nutrient was removed with the grain when the crop was harvested. It compared hybrids with the rootworm resistant trait against a sister hybrid without the rootworm resistant trait.

In one study, (conducted in Champaign in 2008 and 2009 and in Dekalb in 2009) rootworm-protected hybrids averaged 10% greater yield (171 bushels per acre vs. 188 bpa) and removed more nitrogen (8%), phosphorus (12%), potassium (9%), sulfur (9%) and zinc (12%) compared to non-protected hybrids. Yield responses were more variable in the second study (Champaign and Dekalb in 2010). For those rootworm resistance hybrids that did respond, the yield averaged 9% greater (225 bpa vs. 245 bpa) and had greater post-flowering uptake of nitrogen (31%), phosphorus (24%) and potassium (38%).

Below told DTN the results suggested the rootworm-resistant trait keeps roots active longer and there is better post-flowering uptake of nutrients. "Sometimes we saw phosphorus and zinc concentrations go up in the grain of hybrids with the [rootworm] resistant trait. We believe this suggests that phosphorus and zinc may have been limiting yield in non-rootworm resistant hybrids," Below said.

He believes the reason there was a strong response to phosphorus and zinc is that these nutrients are immobile in the soil. It takes a greater root mass or longer periods of root activity to retrieve these nutrients. Because phosphorus and zinc are immobile, uptake is driven either by root interception -- roots grow to the nutrient source -- or diffusion to the root.

"We also found that rootworm-resistant hybrids use nitrogen fertilizer more efficiently than the conventional hybrids," Below said. "The recovery of applied nitrogen was greater and we got more yield per unit (of) nitrogen. The better you protect the roots, the more likely you can access nitrogen and the better return you will get."

Below maintained that feeding the crop based on soil tests isn't enough. He noted that the nutrient removal rates agronomists and growers rely on are decades old and often don't reflect the higher yield potential of modern hybrids. Routinely short-changing the crop can have long-term yield implications and become the equivalent of mining the soil. "Growers can do their own experimenting with rates on their farm. They can also test for nutrient concentrations in the grain and using the data, along with grain yield, calculate what the crop is actually removing," he said.

"I want growers to reassess their fertilizer applications and not do the same thing as they've been doing the last 20 years. They need to consider using sulfur and zinc and take advantage of new fertilizer technologies so that nutrients are available at the right time and in the right nutrient balance. Begin to consider new products and better placement."

(PS/CZ/SK)

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