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Is split N really best?

The debate continues, with a focus on technology, soil and weather — and then being prepared to break with tradition

Advances in technology are driving many on-farm practices, creating operating efficiencies and production advantages. From robotics and variable-rate technology all the way back to the first GPS yield monitors, new systems and designs have changed and will continue to change the way farmers farm.

Splitting or delaying nitrogen (N) applications in corn is different, and it’s fraught with all kinds of provisos and considerations, not to mention controversy.

It isn’t hard to come up with a reason to reject splitting your N. Some farmers cite workload issues. Others say that today’s technology just isn’t precise enough for them to accurately model what’s going on in their fields, while others simply see no need to change because they argue that traditional practices are working well.

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In the end, when it comes to splitting their N, there are some who do, some who won’t, and a whole bunch who will consider it if the growing season seems right.

The one unifying theme to splitting applications is that it can be a benefit, even though there are several caveats. Among them are: the type of growing season, weather conditions (at planting or prior to the targeted date for split application), soil type, planting dates, and the grower’s acceptance of risk. Many who have embraced the practice have found a sweet spot, yet most have taken several years to adopt the technology and then to gain the familiarity and do the fine-tuning required to make it actually pay.

Mike Strang is a grower from the Exeter, Ont. area, and he’s been a dedicated user of the Y-Drop system in his corn for several years. Strang has combined that with an OptRx crop sensor which takes a reading of the plant and interprets the amount of nitrogen (N) needed. The interpretation is based on readings Strang takes from a high-N strip applied weeks earlier, or from an area of the farm he knows has the best soil.

He drives through slowly, allowing the OptRx to establish N-sufficient readings. When he applies N to the rest of the field, the unit takes the current readings, compares them to those previous N-sufficient figures, and calculates the appropriate rate.

Strang concedes that what has worked on his farm has taken time for adjustments, and he does acknowledge the added workload and logistical challenges with later-season nitrogen applications.

“Some people find it simpler just to get it done all at once at spring planting and forget about it.” he says, adding that other crop demands, herbicide applications, livestock production or midsummer vacations can divert from split applications. “But I grew up side-dressing with my dad, and we’ve been side-dressing all the time, so it’s just natural for me.”

Despite his familiarity, Strang talks of two accepted numbers: 1.2 pounds and 20 per cent. Corn takes 1.2 pounds of N per bushel, so a 200-bushel crop would need 240 pounds of N per acre. Then, 20 per cent refers to the potential reduction in nitrogen needed when the nutrient is supplied at side-dressing. That benefit is well established, although the technology that can help bring it to a farmer isn’t quite as well accepted. Technologies such as Y-Drops, Veris or OptRs are relatively new and there’s still a lot of debate about their benefits.

“In those areas where you’re going to get that yield, that soil will actually supply a lot more nitrogen than we give it credit for,” Strang says. “I think there’s still that mentality out there that if you want higher yields, you need more nitrogen, but that’s not actually true. The research is getting well established that corn does take up a significant amount of nitrogen, post-tasseling. But does it actually benefit using the Y-Drop and passing as close as possible? There’s some debate about that.”

Strang maintains that split applications make more sense — to him — considering there’s that much more of the season and the wet weather behind him. The corn crop at that point is also giving a grower a better picture of its total nitrogen needs, better than it can when it’s, say, only five- or six-leaf.

Cheap insurance

A common belief among many nitrogen applicators is, “I’d rather over-apply and lose money than under-apply and lose yield.” It may be a sign that says farmers as a group are over-applying nitrogen in the name of protecting yield, yet Strang understands the benefit of reducing workloads and minimizing risk.

“That’s our mantra in agriculture, where we’re always happier to put a little extra on because it’s cheaper to do that than lose yield,” Strang says. “What I really like about it is that I’m trying to fine-tune my N-rate, and I’m doing it on variable-rate, as well, and that’s almost impossible to do if you apply everything at planting. By side-dressing and especially doing it late-season, I have a better chance of getting close to that optimum nitrogen rate and wasting as little as possible but still get the most economical yield.”

Keith Reid puts a different spin on the “over-apply versus under-apply” mind-set, calling it a false economic argument. He agrees with Strang’s observation about over-applying nitrogen as cheap insurance, but to justify it in the name of yield is similar to “a dollar saved is a dollar earned” — but perceiving the dollar earned is more valuable.

“That’s not the reality,” says Reid, a soil scientist with Agriculture and Agri-Food Canada. “The difference is that if you wasted $30 per acre on nitrogen, you’d probably never know it — your yield was good, the crop was good and you had no idea you spent far more money on nitrogen than you had to. If you under-applied that same amount, the impact on the crop would be visible.”

A popular, if not debatable, sentiment in corn production states “I’d rather over-apply and lose money than under-apply and lose yield.”
photo: Supplied

Reid also echoes Strang’s comment that split applications or side-dressing aren’t things everyone wants to do, even if sensor readings or pre-side-dress nitrate test (PSNT) results advocate for it. Nitrogen applied all at once at the start of the season alleviates having to drive across the field more than is thought to be necessary, and as Reid points out, the real or perceived benefits to side-dressing have been inconsistent.

“We talk in terms where side-dress or top-dress or split applications should improve nitrogen-use efficiency and you should get more bushels of corn or wheat per pound of N by finely tuning the nitrogen applications,” says Reid. “Yet it doesn’t always happen.”

Some of that is because weather conditions between planting time and when the crop needs the nitrogen may not cause the losses that would make side-dressing a benefit.

“We know how to side-dress nitrogen — it’s been done for a number of years — but it works well in some soils but not well in others,” explains Reid, adding that flat clays are more responsive than rolling hills with lots of stones. “If a grower is going to use UAN instead of urea, then they’re handling more product — because it’s 28 per cent instead of 46 per cent. Whether you’re using Y-Drops or a knife down the middle of the row, it’s going to be more product to handle.”

Reid wonders if the debate can be re-framed: Is there a consistent advantage to splitting N applications under Ontario conditions, in terms of reduced N rates or higher yields? And is that advantage for all crops and soil types or just some crops or soils? If the advantage varies one year to the next, is it enough in the responsive years to cover costs in the non-responsive years?

Another concern is whether there’s an additional advantage from split N applications using new technologies to fine-tune rates accounting for variability in the crop N status, variability in the N supply from different soils under different weather conditions, or variability in the losses of early season applied or mineralized N from different soils under different weather conditions.

What’s missing?

Whether it’s among the adapters, the skeptics or those who remain undecided on split applications, another common thread is what’s missing to persuade farmers away from the “all-at-once, all-at-the-start” approach. According to Paul Hermans, the best technology to enable growers to pinpoint their best rate (i.e. the maximum economic rate of nitrogen) isn’t widely available here in Canada.

For the past three growing seasons, Hermans has been involved in a joint research project involving soil and crop improvement associations in three county chapters in Eastern Ontario — Ottawa, Dundas and Lanark. The study involves various treatments across 10 farms, comparing six different rates applied (starter only, 75 per cent grower standard with Y-Drops, grower standard, grower standard with Y-Drops, 125 per cent of grower standard with Y-Drops and 125 per cent of grower standard).

(Results from 2015 and 2016 are available at the OSCIA website — go to Environmentally Sustainable Utilization of Nitrogen on Corn — PDF, 2016 and 2015.)

Among the highlights from the first three years of the project (although 2017 results aren’t posted yet), Hermans stresses there are significant differences between soils in eastern Ontario and those in the southwest, and those differ from Quebec or the Maritimes. They’re enough to skew the results from side-dressing or split applications.

“If you looked at the data in our area, you would see a split application doesn’t pay,” says Hermans, the digital effectiveness manager for DuPont Pioneer. “But with the Veris-generated data, when you look at the sandier soils or the heavier clays, that’s where it seemed that we were picking up a bit of an advantage to Y-Drop. When you compared the loam soils, a split application didn’t seem to pay.”

The underlying point is that the technology is still part of the adaptation phase. It’s not just the farmers who are learning how to use Y-Drops, Veris, OptRx or even GreenSeeker technologies. Advisers, agronomists and researchers are also trying to refine the generated numbers in an effort to pinpoint exact amounts and efficiencies.

Hermans also believes a large impediment in split applications is the lack of soil data. In the U.S., growers have a nitrogen model which provides a digital compilation of conditions at one-, two- and three-foot increments based on soil structure. With two inches of rain, for instance, growers can see topography, water infiltration and how much denitrification occurs, and from there, generate a model that helps the grower to predict nitrogen rates.

Unfortunately, that system doesn’t exist in Canada… yet.

But the other shortfall in the struggle for understanding with split applications is the lack of awareness — across agriculture — of soil interactions during the growing season. How much nitrogen is “cookedup” by the soils, asks Hermans. How much nitrogen does the soil supply on its own? In order to determine that, a grower has to distinguish all that’s happening in specific soil or “decision zones” in a field, check soil organic matter levels and conduct some type of soil nitrogen test. Only then can they decide where they are with regard to split applications.

“The technology can work, we just have to have a better understanding of where it works, and use it based on soil type and weather patterns,” says Hermans. “It’s easy to put all the nitrogen on up front, where you don’t have to worry about it. But then what happens from the weather standpoint, and worrying about whether you made the right decision? We need to see how our soils work with less nitrogen, what capabilities do we have to cook some nitrogen, and go from there.”

Total package

On the equipment front, Reid acknowledges that there is a wealth of technologies available; however, he believes the hardware and software are ahead of the adoption curve.

“We have lots of tools out there that might be able to help us fine-tune nitrogen application, but none of them is to the point where they’re really reliable yet,” says Reid, reiterating that it’s a tool, not a silver bullet. “If you’re just managing one part of that system, you can get something that comes up that you weren’t watching for. You won’t get a good response to nitrogen no matter how tightly controlled your rates are, if something else is limiting the growth of the crop.”

In the case of using Y-Drops, it’s not that the system represents a huge change in the way of managing nitrogen applications, it’s just one more tool to do the job.

“One’s a vice grip and the other’s a crescent wrench,” says Reid, adding that there’s still a fundamental knowledge base that goes with getting the most out of any tool.


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