Recalculating wheat nitrogen
By: Staff Report, AgWeek
In the wake of 2009’s dismal protein numbers, North Dakota wheat growers may be able to take heart, now that they can arm themselves with more accurate nitrogen recommendations, thanks to Dave Franzen and several of his colleagues with the North Dakota State University Extension Service.
The new nitrogen calculator takes into account both soil testing and previous crop credits, as does the more basic decades-old formula, then goes a few steps further, calculating in values for soil productivity, types of tillage, soil organic matter and a cost-return value for based on the cost of nitrogen and value of wheat.
“I think this is such a huge step forward. I’m really excited about it,” Franzen says.
Grower response to the North Dakota Wheat Nitrogen Calculator has been “overwhelmingly positive” since its December release, the extension soil specialist says.
The most accurate calculators typically use the most data to come up with their answers. In 2003, Franzen began going over nitrogen usage archives that had been collected in North Dakota since the 1970s. In 2005, he received funding to start new nitrogen trials in several parts of the state.
“From 2005 to 2008, we collected about 50 site years of data from around the state and added into that were 50 site years of archive data from 1970 to 2005,” he says. “So we have about 100 site years of data encompassing the state.”
One of the first things he looked at was the relationship between yield and nitrogen rate without regard to soil test data. There was a relationship, but it was not clear, he says.
“When I put the soil test nitrogen in there, the relationship really improved a lot, so there’s a reason why we ask people to soil test,” he says.
Next, he considered the different growing conditions around the state.
“A logical separation is the east and the west,” he says. “But another thing that I’ve seen since I came here about 15 years ago was that the Langdon area is just strange. Sometimes during the growing season, the flax falls down, the spring wheat falls down, the durum falls down and the barley can fall down at just normal nitrogen rates.”
He decided he’d gotten enough data from the Langdon area to separate it as its own special growing area, apart from eastern and western North Dakota. The area enjoys good wheat-growing weather with its cooler summertime conditions, and the soil organic matter is on the high side.
Franzen analyzed the data from the three regions separately, calculating the equation for the relationships between the available nitrogen and yield and the available nitrogen and protein content.
“Once you get that, you can predict the yield that you’re going to get,” he says. “And once you get that, you can look at the price of the wheat and the cost of the nitrogen and you can work out what’s called a return to nitrogen relationship.”
He uses this relationship to figure out what the optimum nitrogen rate is, based on the maximum economic return for nitrogen using wheat price targets from $3 to $10 a bushel and for nitrogen costs from 20 cents to $1 per pound. The nitrogen rate recommendations range from zero to 250 pounds per acre.
“Then from there, you subtract off your soil nitrate test and then you subtract off any previous crop credits,” he says.
This is done by entering the soil nitrate value and selecting from among eight options for previous crop credits. Four of these options relate to alfalfa and sweet clover, two to sugar beets and one to soybeans, field peas, dry beans, lentils, chickpeas or harvested sweet peas. The last option denotes a crop that supplies no nitrogen to the soil.
Added to the calculator is a feature that Franzen considers unique to this type of decision-making tool.
“There were long-term no-tillers that were coming up to me and saying, ‘We really need to do something about these nitrogen recommendations because I started backing off my nitrogen rate several years ago and never looked back,’” he says.
Long-term no-tillers, those who have employed the process for more than five years, have learned that they can get by with significantly less nitrogen.
“When we did that, you know, those long-term no-tillers were right. In order to hit a specific yield, it took at least 50 pounds less of N in no-till than it did in conventional till,” Franzen says.
To hit a certain protein target, no-tillers apply 50-plus pounds less nitrogen than conventional tillers.
But the five-year benchmark is critical.
“If you’re a beginning no-tiller, from one to five years or something like that, it actually takes a little bit more nitrogen because the residue ties it up for a period of time and it doesn’t get used right away,” he says. “So if you’re a short-term no-tiller or you just no-till part time . . . there’s a 20-pound tack-on. But if you’re a long-term no-tiller, six years or more, there’s a 50-pound credit.”
The calculator handles all this, allowing selection of long-term no till, short-term no till and conventional till.
Unfortunately, there was not enough no-till data in the Langdon area to allow Franzen to incorporate tillage practices in that area’s calculations.
In areas that have significant amounts of organic matter in the soil, the nitrogen recommendation can be further refined.
“You really don’t worry about that unless you have 6 percent organic matter or more,” Franzen says.
About 2 percent of the soils in the state are such soils, often as small portions of crop fields.
“It’s not a lot of acreage, but if you’re a farmer who has 10 or 15 acres in the middle of a field someplace, it’s something that you need to pay attention to,” he says.
THE FINAL NUMBER
Once the data is entered, the final nitrogen recommendation is displayed as a pounds-per-acre value in a blue box near the bottom of the screen. A note is included next to it, advising the grower to consider a rate within 30 pounds of the number.
“Whether they go higher or lower, that number is kind of up to them,” Franzen says. “They’re supposed to use their common sense. So if you have a low-protein variety, then you probably need to beef it up a little bit. If you’re using a less-than-optimum nitrogen application method, like putting urea over the top and not working it in, or a shallow application of ammonia, you need to beef it up a little bit.”
Also, the amount of straw left on the field can affect nitrogen needs. The standard amount of wheat straw left on an acre is about 2,000 pounds.
“This year, we probably have twice that much in some fields,” he says. “So if you have 2,000 pounds more residue than what you plan on — like if you grew 80 or 90 bushels of small grain instead of 40 or 50 — then you need to add about 30 pounds of (nitrogen) to take care of what that straw is going to tie up this next year.”
This is clearly stated below the final number.
SO FAR SO GOOD
Response to the new recommendations has been generally good, Franzen says.
“You know whenever you do something new you’re always worried about change,” he says.
But according to comments he and his colleagues have received, once people understand how and why Franzen updated their recommendations, the response has been “overwhelmingly positive.”
The North Dakota Wheat Nitrogen Calculator is free to use and available at www.soilsci.ndsu.nodak.edu/wheat.