MINNEAPOLIS, Minn. – Corn yields in North America have doubled in the past 50 years, and plant genetics developers expect them to double again in the near future.
However, increased yields are of no value unless they economically benefit the farmer, says Dan Froehlich, chief agronomist for Mosaic, which specializes in concentrated phosphate and potash fertilizers.
Froehlich said corn yield increases are partly based on the introduction of hybrids with stacked traits to fend off attackers.
Stacked trait varieties accounted for nearly half of all corn grown in the United States this year.
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However, the recent introduction of improved hybrids with resistance to the corn rootworm larva brought surprises.
Froehlich said if a new trait provides a 14 percent yield bump, it’s logical to expect the crop to use about 14 percent more nitrogen and other nutrients.
But that wasn’t the case in a recent study conducted at the University of Illinois in conjunction with Mosaic that included varieties with stacked traits for Roundup Ready and European corn borer and others that also included rootworm resistance.
Research found higher-than expected uptake of phosphorus, zinc, sulfur, boron and micronutrients in the rootworm resistant crops.
While the yield increase was 14 percent, excess nutrient consumption was 17 to 27 percent.
Froehlich said this sudden nutrient uptake didn’t occur when other resistance traits were layered into the plants’ genetics.
“In fact, the (uptake) difference was less than the yield increase. When corn borer resistance gave us a 10 percent yield increase, the increase in nutrient uptake was only seven or eight percent.”
That’s because corn borers affect only the head, which means the resistance focuses only on protecting the kernels. It doesn’t affect the internal plumbing of the plant.
“But with rootworm resistance, we’ve changed everything. Now we have a much bigger, healthier root. The corn plant establishes quicker and deals with stress better.”
A bigger, better rootball will do a better job of accessing nutrients and moisture, and it will reach out further than a root affected by rootworm larva.
But why does it use up all those nutrients?
It goes back to basic plant science. Every crop has a chief yield-limiting factor. In recent years, corn’s yield-limiting factor has been the rootworm larva. Removing the rootworm threat changes the plant’s growth characteristics and physiology.
While it may be a while before all the details are documented, Froehlich said the introduction of rootworm resistance has forced the corn plant to build proteins that it’s not accustomed to making.
“This brings up a lot of questions: are the fertilizer recommendations from soil test labs relevant to the new genetically stacked hybrids?” he said. “Most of the response curves were generated 30 years ago, based on average corn yields at the time. They simply extrapolated those numbers out to cover higher yields. Do we now have a whole different kind of nutrient requirement for these multi-stacked hybrids?”
Froehlich said there’s a downside for growers as the pile of stacked traits gets higher. The problem farmers already experience with Bt root balls will get worse in striving for higher yields.
Not only will root balls grow, but so will the overall biomass.
At any stage from harvest to planting, stalks can be chopped, cut, pulverized, baled or simply pushed out of the way by an aggressive trash management device mounted on the planter.
Root balls are a bigger challenge. “They’re like rocks. You can’t mince them up like you can the stalks. When we put more of that Bt stuff in there, the roots get tougher and they last longer. I don’t know of anyone yet who’s working on ways to make that root ball more biodegradable.
“If we’re looking at higher yields and higher plant populations, then we’re looking at more root balls and they’ll be more robust.”
