Choosing protein or yield
There are so many things in agriculture that could make life easier every year, if we could just figure out how to do it. For example, wouldn't it be nice if we could permanently eradicate plant pests and disease from our fields? Or know for cert...
There are so many things in agriculture that could make life easier every year, if we could just figure out how to do it. For example, wouldn't it be nice if we could permanently eradicate plant pests and disease from our fields? Or know for certain what the weather is going to do for the next six months? How great would it be if wheat producers didn't have to choose between yield and protein?
Well, we aren't quite there yet, according to Jochum Wiersma, small grains specialist with the University of Minnesota-Crookston. But it certainly is worth looking into.
"Growers are interested in having varieties that have high yield and high protein. We need to understand better what makes a high-protein variety a high-protein variety and vice versa," he says.
One or the other
Right now, producers have to choose their varieties for either protein or yield performance. A Kelby or a Glen variety may deliver impressive grain protein levels, but will produce significantly fewer bushels per acre. On the other hand, a Samson or Traverse may yield more bushels per acre, but deliver marginal protein. And somewhere in the middle, Granger and Sabin offer mid-range performance in both categories.
Most varieties come with some added traits such as drought tolerance or disease resistance. None of them offers high levels of both, so growers have to decide whether to sacrifice protein for yield or yield for protein, often depending on what the market and weather gurus see in their crystal balls.
Think of a wheat plant as having two engines in it. One of them cranks out piles of protein and the other produces piles of starch, the stuff of grain fill. Both are consistent performers, but the protein engine runs at a slightly lower rate than the starch engine, so it produces at a slower rate.
They start off even at the beginning, but the longer these engines run, the more the starch pile begins to overshadow the protein pile.
"Since we measure grain protein as a percentage of weight, we dilute it," Wiersma says. "The total amount of protein is higher, but we dilute it with more starch."
And if weather conditions are favorable for wheat -- in other words, cooler temperatures and adequate moisture -- the grain fill lasts longer and plant maturity is delayed.
"The end result is that you, over time, produce more starch than you produce grain protein," he says.
This is why higher-yielding crops have the tendency to deliver lower protein content.
Eighty percent of the nitrogen that's eventually going to end up in the kernel as protein already is taken up before anthesis, or flowering.
"It's basically being recycled out of all the enzymes, the RuBisCO (enzyme) and everything that is associated with photosynthesis and ends up back in the kernel," Wiersma says.
The remaining 20 percent of nitrogen is taken up during grain fill. But there's something else going on in our production system that puzzles Wiersma and his colleagues.
In recent trials at five locations, the maximized yield was at about 1.7 pounds of nitrogen per bushel of yield attained.
"That's about 33 percent less than what the current recommendation is," he says. "In our production system, we apply, basically, surplus nitrogen for yield, to be able to obtain high grain protein content."
He surmises that it is possible to maximize yield long before protein content is maximized.
"If all I'm doing every single year is producing the same amount of protein and diluting it by more or less starch, I have a problem," he says. "That's kind of where we're at right now."
2009 protein drops
Last season's hard red spring wheat harvest brought in record amounts of wheat, but at protein levels well below the 14 percent sought in the market.
Looking back, Wiersma asks the question: "Could we have intervened?"
He says researchers and extensionagents could have stepped in and recommended changes to stave off the low protein. But it would have been difficult because, at the latest decision point in the growing season, anthesis and early grain fill, there were no clear warning signs that differences in grain protein were imminent.
What most likely made the difference was a decrease in mineralization and possibly temporary nitrogen deficiencies caused by excess precipitation, he says.
"In our growing conditions, in-season (soil nitrogen) mineralization is really important," Wiersma says. "We know it is. The problem is that there aren't really good models that predict mineralization precisely enough that we can add it into our management strategies."
As for leeching and runoff, he says most of the nitrogen loss occurs at or very near the surface.
"That doesn't mean that you can't have very acute nitrogen deficiency," he says. "This especially occurs in what I would call a 'pre-five leaf' stage; from the beginning of tillering and head initiation. Your fields turn from nice and green to putrid yellow in about two days."
But technically, that is not nitrogen deficiency, he says. The plant roots have quit working because of a lack of oxygen.
"The way to solve that, if the water runs off quick enough and you want to do something to jump-start those fields, is by applying a little 28 percent (nitrogen) over the top. In very many cases, that will basically get the system going within the plants and alleviate that nitrogen deficiency," he says.
To help stave off another year like 2009, Wiersma and colleague Albert Simms have submitted a grant proposal to study the protein issue more closely.
"The question is, 'Do we have varieties that have differences in nitrogen use efficiency?'" he says. "There's very little in the literature that suggests there are differences. So we don't know. It's not been reported before."
They intend to find out how the varieties differ in nitrogen take-up between anthesis and grain fill and in nitrogen mobilization and how nitrogen is redistributed into the kernels as protein during the growing season.
Are the high-protein varieties just more efficient at nitrogen usage or is there another factor there, and if so, how can it be managed to deliver higher grain protein at harvest?
"Or are they the same efficiency, and from there on, think about different management approaches," he says. "Say, late-season nitrogen or not, and see if we can boost the total amount of grain protein that is produced in a production system."
He says it is very basic field research, during which they will sample the developing plants at several stages of the growing season, strip off the leaves and stems and measure the total nitrogen that's in those plant parts.
"We'll track that over time and see if that differs between varieties, and eventually, at the end of grain fill, if there are differences," he says.
The grant application is for a three-year study.