It’s a fair comment these days that corn production has reached a new level of complexity. Corn is anything but a simple, straightforward crop, even without taking into account the changing economics forced on producers by falling prices, and the constantly shifting mix of imports, exports and trait acceptability,
Now comes research into a specific trait that may redefine corn production in North America.
Since 2008, Dr. Fred Below, crop physiologist with the University of Illinois at Urbana-Champaign, has studied the transgenic rootworm trait and its link to mineral nutrients. His research, published in late 2013, found that rootworm-protected hybrids averaged 10 per cent higher yields (171 bu./ac. versus 188 bu./ac.) and that these yield increases were associated with eight per cent more nitrogen uptake, 12 per cent more phosphorus and zinc, and nine per cent more potassium and sulphur compared to non-rootworm hybrids.
In a followup study, yield responses were more variable, but hybrids that responded to the rootworm trait averaged nine per cent higher yields (245 bu./ac. versus 225 bu./ac.) and they also showed the importance of post-flowering nutrient uptake, averaging 31 per cent more nitrogen, 24 per cent more phosphorus and 38 per cent more potassium uptake during the grain-filling period.
Below began the research right when the rootworm trait was first released, so he could still test rootworm hybrids and their isolines (i.e., the same hybrids, but without the rootworm gene).
He soon found that the value of the rootworm trait was much greater than just accounting for root pruning by the insect. Instead, much of the yield boost seemed to come from enhanced water and nutrient uptake, and from superior plant anchorage (standability). “Some of our earlier work focused on the additional nutrient uptake from the rootworm trait, which only made sense since nutrients enter the plant through the roots. So when we looked at nitrogen, we saw that there’s greater uptake of nitrogen, and in our followup paper, we looked at other nutrients, particularly those that are less mobile in the soil like phosphate and potassium.”
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In the second phase of his research, Below focused on the plant’s uptake of more immobile nutrients, including phosphate and potassium, and how the seasonal uptake of those nutrients was altered by the rootworm trait.
Researchers already knew that corn needs to keep taking up nutrients after it begins grain fill, but in Below’s tests, they were seeing just how much yield response they could get to the uptake of immobile nutrients after flowering.
“Part of this probably reflects the fact that we had an increase in yield, and that increased yield then drives the uptake of nutrients, or maybe it’s the other way around,” says Below.
Asked if this is all occurring as a result of the rootworm trait, or because of some cumulative effect of the nutrients on plant health, Below says he believes the trait allows the root system to more fully achieve its genetic potential.
When insects feed on the roots, the plant ends up with a smaller root system, which means it must expend more of the energy it gets from sunlight to regrow the root system and absorb water and nutrients.
Conversely, when the roots are protected, the root system remains more active for longer. But even then, the effect was even greater than Below expected, based on the rating system used to assess the degree of root damage caused by rootworm beetles.
“That means that the value of protecting the root system is even greater as producers increase their plant densities,” Below says, calling it a “catch-22” situation. “I have to plant more plants to get more yield because each individual corn plant acts as a solar collector. But as I plant more plants, each one has a smaller root system, so its protection is even more important.”
The upshot is clear, Below says. “By protecting the root system, the trait also allows you to plant more plants.”
Dovetails and overlaps
This is where the complexity in corn production starts to build, thanks mostly to the overlap that occurs with each new hybrid that’s released, and the ensuing impact on planting densities, fertility programs, residue and soil management, and of course, hybrid selection. There’s been a considerable amount of press on that latter point in the past six to 12 months, and Below views that as a matter of course.
“Each new hybrid that comes out is five bushels per acre better than the one it replaces,” says Below. But there’s a disconnect. Yields have climbed more than two bushels per acre per year, but fertility recommendations, and the way that farmers fertilize their corn, haven’t changed much in the past 25 years.
“You basically fertilize the same way you did 25 years ago, and in that time your yield potential has gone up at least 50 bushels, meaning there’s a huge yield gap between how we’re fertilizing and what’s possible with today’s hybrids,” Below says. “Part of that yield gap is hybrid protection against the rootworm.”
Part of it also feeds into agronomics, fertility and residue management. This is where the concept of prescription agriculture is becoming more common. The old approach of launching a hybrid and promising that it will give excellent performance everywhere is being replaced with an approach of trying to match the genetics specifically to local conditions and management.
Below notes that the producers who are winning corn yield competitions in the U.S. with yields topping 400 bu./ac. are forever pushing densities and fertility. And although his research indicates a certain amount of neglect for phosphorus, sulphur and zinc, nitrogen is the default nutrient to apply.
Being mobile in soils, nitrogen requires special management, but it’s still the most visible return on fertilizer investments. It’s the easiest control in the “control the controllable” discussion.
“Actually, I’ve put adequate weed control, soil test and soil fertility as prerequisites (in the “Seven Wonders of the Corn Yield World”), because if you built up your soil fertility, you didn’t need to fertilize as much. It was sort of money in the bank,” says Below.
“But a lot of growers have not maintained that bank account,” Below believes. “Low soil tests are a bad thing, but I don’t think that the soil test data are necessarily calibrated to today’s high-yield potentials, especially when we run the plant density up. Soil test calibrations weren’t done under high densities, and they weren’t done with the yield potential of the hybrids today.”
The bottom line is, farming is mining the soil to produce some incredibly high yields. But the industry isn’t adequately replacing those nutrients. And it’s going to catch up to us, Below says.
Below has also looked at uptake patterns, recognizing this work hadn’t been updated in nearly 50 years.
“What you find — not surprisingly — is that not all nutrients are taken up at the same rate or over the same time,” says Below, adding that phosphorus, sulphur and zinc are key nutrients that exhibit season-long uptake. “Half of these elements that the crop needs have to be taken up after flowering. So if you have roots that act longer after flowering and you have some nutrients where half of their uptake has to come after their flowering, those are the ones that are going to be potentially more benefited.”
The same yet different
Alan McCallum is a certified crop adviser from Iona Station, Ont., southwest of London, and in a wet year such as 2014, he has seen more impact in yield data than symptoms in the field. And he agrees with Below’s assessment of weather and nitrogen application, and their values in terms of yield.
“The one thing I can say for sure is that we’re removing more nutrients than we used to,” says McCallum. “Whatever changes we’ve made to that hybrid, we are producing those bushels and we are removing those nutrients.”
Where McCallum has questions, however, is on why the large root systems in today’s hybrids aren’t doing a better job of accessing more nutrients.
But that’s not happening in his opinion, and that’s the biggest concern. Whether the corn rootworm trait is a part of the discussion isn’t as big an issue for growers on this side of the border, he believes. It all comes down to meeting nutrient demand.
“For the most part, if we’re planting corn on corn on all but the coarsest-textured soils, we’d better have corn rootworm protection in our genetics,” says McCallum. “If we’re on rotated ground, I just want to pick the best hybrid, and the way things are shaking out in my area this fall, some of the best performing hybrids don’t happen to have the CRW trait.”
That, he adds, is something of a testament to our growing conditions. Rootworm pressure is not as severe here in Ontario or Eastern Canada as it is in the U.S. Midwest, and McCallum is quick to agree that rotation has a lot to do with breaking the cycle on the pest. But circling back to the nutrient issue, there is more to be learned, and not only with phosphorus and potassium levels. Even sulphur and now zinc are being mentioned more in the recommendations.
“I haven’t done a lot of recent side-by-side trials, but the increased appearance of zinc-deficiency symptoms also has to be on our radar,” says McCallum. “We have to be considering that 200-bushel corn crop does have a pretty significant demand for zinc as well.”
With sulphur, there’s less environmental deposition, which has coincided with increased crop removal, and in some cases, with decreasing organic matter in the soil. On the other hand, sulphur is one of the trickier nutrients to sample for, and McCallum hasn’t seen large correlations between a soil sample and eventual deficiency symptoms. On top of that, it’s hard to say that all soils need added sulphur, although some will respond to the practice.
‘Factory farming’
Doug Alderman likens a corn plant to a factory, and if you’re going to demand more output from a factory, you’re going to need more input. He finds it frustrating that some growers limit their fertilizer applications yet expect their soils to keep yielding more.
“The genetic native traits through plant breeding and transgenic traits have allowed us to increase our yields, partially by increasing our populations,” says Alderman, national sales manager with Pride Seeds, based in Chatham, Ont. “But in planting higher populations, it only stands to reason that we’re going to be removing more nutrients. It’s not the trait itself that requires more nutrients, it’s because the trait is protecting the roots, making them a better pipeline to transport the nutrients to the plant.”
Alderman sees a potential nutrient shortfall in a rotational pattern. Corn isn’t the only crop that suffers from rationed fertility programs. Each crop in the rotation ultimately affects each other. Apply 95 pounds of phosphorus per acre for corn, says Alderman, and that translates to approximately 14 to 15 pounds per acre available for next year’s soybean crop if no additional phosphate is added. That’s not enough to produce potential yields in the mid-50s to upper 60s.
“A soybean crop removes more than twice as much potassium as it receives in the form of fertilizer, so if they’re supplying next year’s crop via corn, or another year of soybeans, we’re going to see some deficiencies the following spring,” says Alderman.
Commenting on Below’s research, Alderman agrees with the correlation between corn rootworm protection and enhanced plant health, including a strong root system.
“It’s like a water hose,” Alderman says, “Squeeze the hose and you won’t get as much water at the other end. Get a bigger hose (root system), and you have more output.”
And as for post-flowering, Alderman is quick to add his voice to the discussion, noting that maximum uptake rates of certain nutrients occur late in the vegetative state, and the uptake of nutrients such as potassium, sulphur and zinc is greater during grain fill.
“Applying the right nutrients at the right rate at the right time and in the right place in order to meet the demands of the crop has a direct impact on plant health and being able to fend off stress, be it weather or pest related,” says Alderman. “It isn’t one single facet that affects corn production, it’s a combination of uptake levels of nutrients through a healthy root system and protecting plant health with traits and further through fungicides later in the growing season.”
