Today’s biggest issues in soil fertility

When to broadcast, shallow band, deep band and top dress

Rigas Karamanos, a senior agronomist with Koch Fertilizer Canada, is one of the leading Canadian experts in soil fertility today. After speaking at hundreds of producer conferences and research symposiums, Karamanos says there are four major topics that come up again and again at every discussion of agricultural soil fertility.

Broadcasting, shallow banding, deep banding

There are rarely enough hours in a day to perfectly optimize every component of farming, especially as farm sizes increase. While farmers know deep banding nitrogen at seeding is ideal, broadcasting can allow faster seeding. In fact, fertilizer is being applied in the fall to more Prairie acres for exactly this reason, especially on larger farms.

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Why it matters: Farmers who understand the risks and rewards of various fertilizer placement and timing methods will benefit financially.

“It’s not always about agronomic efficiency; it’s operational efficiency. Dr. Ross McKenzie did research in southern Alberta that showed every day you seed past May 1, you have the potential to lose yield. For example, for wheat, it was 0.8 per cent per day. So, I do understand why people want to seed as fast as they can,” says Karamanos.

“I talked to a farmer here in central Alberta who said he was able to reduce his seeding time by 40 per cent by using his nitrogen tank to store more seed, so he didn’t have to refill so often.”

Farmers who opt to broadcast, especially those who fall broadcast, should use a stabilizer to reduce volatilization and denitrification losses, says Karamanos.

“Research shows you do get a benefit by having a stabilizer. The wetter it is, the more the benefit. People use it as an insurance: under very dry conditions losses are minimal and it will not make a difference, but if you get moisture, it can make a big difference.

In a project we had with UAN, where we applied 70 per cent of the recommended rate and subsequently top dressed the remaining 30 per cent, we received yield increases in the order of 15 bushels of wheat per acre by using an inhibitor in moist conditions.”

Because deep banding isn’t always possible, understand the risks of broadcasting and shallow banding.

“If you broadcast urea and only get one-tenth of an inch of rain for a few days, your losses can be as high as 50 per cent. If you get a half-inch of rain, maybe your losses are five to 10 per cent. You’re never going to get zero losses,” says Karamanos.

The very worst-case scenario is morning dew, which can translate to losses as high as 60 to 70 per cent because it gives enough moisture to hydrolyze (break down) the nitrogen but not enough to wash it into the soil.

Interestingly, shallow banding isn’t always better than broadcasting, however.

“There’s some really good work by Agriculture and Agri-Food Canada showing that shallow banding can be worse than broadcasting for nitrogen loss in some situations,” says Karamanos.

How can this be? If farmers broadcast onto dry ground, the nitrogen can’t volatilize and escape because there’s no moisture to hydrolyze the nitrogen. Thus, it just sits on the surface until adequate moisture occurs (ideally, a heavy rainfall to push it into the soil). However, if farmers shallow band into dry soil, the dry soil will likely still have enough moisture to start to break down the nitrogen.

When the nitrogen breaks down, it releases bicarbonate that raises the soil pH. Higher soil pH translates into more volatilization, so a high percentage of the nitrogen will be lost without any washing into the soil.

While volatilization does happen with deep banding in dry soil, the soil on top of the nitrogen absorbs the volatilized gases so actual losses are much lower.

Top dressing for yield

This year, there is significant interest in top dressing, primarily because challenging spring conditions across much of the Prairies meant many farmers weren’t able to apply nitrogen at, or prior to, seeding. The window to top dress without a yield sacrifice is open in cereals until the first node is visible and in canola until the crop reaches the six-leaf stage — so long as rain occurs soon after application.

Making the most economically and agronomically beneficial decisions about fertilizer timing and rate is extremely difficult, even for researchers.

That’s because the biggest factor in nitrogen’s uptake versus loss calculation — precipitation — is so unpredictable.

In 2005, Karamanos and several colleagues conducted nutrient uptake trials that showed just how critical precipitation is to nitrogen investment.

The research team divided each of two sites in Manitoba and two sites in Alberta into halves. On the first half at each site, they applied the full recommended rate of fertilizer at seeding.

On the second half, they applied 60 per cent of the recommended fertilizer rate at seeding and 40 per cent top dressed at week six. Then, the researchers monitored nutrient uptake weekly from planting through harvest.

By chance, the four sites received entirely different amounts of precipitation: one site was extremely dry almost throughout the growing season, two sites recorded near- normal levels of precipitation and one site received an unusually high amount of rain.

“What we found out is where we had zero rainfall for seven weeks, we’d have been a heck of a lot better to stay at the 60 per cent application rate because the 40 per cent addition didn’t add anything. There was no nutrient uptake spike,” says Karamanos.

Where there was normal precipitation throughout the season, the team got the same yield on both halves of the sites, which showed timing of application didn’t matter. Where there was excess rain, the team captured a seven-bushel-per-acre benefit from adding the final 40 per cent of nitrogen at six weeks rather than at seeding.

“How do you know what you’ll get for weather? That’s the thing. You have to make your best guess and then live with it,” says Karamanos.

Top dressing for higher protein

Some years, farmers can achieve a significant premium for high-protein crops. Top dressing after the first node in cereals or six-leaf stage in canola supports protein rather than yield. Those interested in top dressing for protein should aim for application (with adequate precipitation) as close to flowering as possible. That said, in many years, chasing protein only translates to added cost.

“What we found in the work we did is that applying nitrogen for protein is a high-risk practice in Western Canada. The economics are not always there because you never know if there’s going to be a protein premium,” says Karamanos.

Research out of Melfort, Sask., shows applying an extra 15 to 20 pounds of nitrogen at seeding can — given ideal moisture — give the same protein benefit as a late nitrogen application. However, in dry conditions, applying the early boost of nitrogen can prove costly because of both the upfront cost of the fertilizer and a higher incidence of crop lodging.

One thing that is certain, Karamanos says, is — except in very limited situations — adding supplemental sulphur offers no protein benefit.

It’s also important that producers recognize the protein limits a crop can reach, even with ideal nutrition and weather.

“Protein content is very much a function of the cultivar. No matter how much fertilizer you put down, you won’t get higher protein than the potential of the cultivar,” says Karamanos.

Phosphorus depletion

Whereas farmers are very conscious of each crop’s nitrogen needs, Karamanos worries about yield loss across the Prairies due to phosphorus deficiency.

Based on the IPNI (International Plant Nutrition Institute) 2016 survey, phosphorus levels were below a critical level in 59 per cent of Alberta, 81 per cent of Saskatchewan and 64 per cent of Manitoba farmland acres.

“That directly impacts any crop,” he says.

While Prairie soils are prone to low phosphorus to begin with, the issue has been intensified by the high phosphorus demands of today’s highyielding varieties.

“We’ve got all these new varieties that take more phosphorus than you can easily put back in,” says Karamanos.

“A 60-bushel canola crop will remove 55 pounds of phosphate per acre. You can’t replace that. You can’t put down enough with the seed because you’ll injure the crop.”

Karamanos isn’t alone in this concern.

Last year, he was part of a 10-member panel addressing the issue at the annual Soils and Crops Workshop in Saskatoon. Together, the group recommended several strategies for managing phosphorus deficiency.

The best strategy, says Karamanos, is to adopt side banding. Placing phosphate an inch to the side and an inch below the seed, “allows you to put a heck of a lot more phosphorus on than you could directly with the seed.”

As importantly, however, is to shift toward a multi-year strategy. Most farmers know that cereals, depending on soil conditions, can generally tolerate more than twice as much phosphate as canola and up to five times as much phosphate as certain legumes.

However, the concept of adding phosphorus for future years hasn’t significantly caught on, says Karamanos.

“We have to start thinking a little bit different. What you need to do is load the system in a year that the crop can tolerate it.”

Ultimately, all soil fertility decisions should be made with 4R nutrient stewardship (using the right fertilizer source, at the right rate, at the right time, with the right placement) in mind. The 4R approach, which is endorsed and supported by the International Plant Nutrition Institute, The Fertilizer Institute, Fertilizer Canada and the International Fertilizer Industry Association, offers enhanced environmental protection, increased production, increased farmer profitability and improved sustainability.

“Unfortunately, we don’t know what the weather will be. In farming, we’re always taking risks. But using the 4R principle means you’re getting economic benefit and you’re being socially and environmentally responsible too,” says Karamanos.

Madeleine Baerg is a freelance writer and communications consultant who specializes in all things agriculture.

 

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