Top dressing fertilizer over a growing crop could be a good economic strategy in the Brown Soil Zone, where moisture can be hit and miss at seeding time

Whether split applications of fertilizer can improve crop yields or reduce the risk of applying more nutrients than the crop can use may depend largely on the crop and where you farm in Western Canada.

In the Black Soil Zone where growing conditions are generally favourable, researchers and farmers have found little value to a system where roughly half the nitrogen is applied at the time of seeding, and the rest goes on at some point before emergence of the flag leaf. But in the Brown Soil Zone, researchers and farmers say the split application is certainly a good tool for managing risk and fertilizer costs, especially if conditions are dry at seeding or if they expect moisture may be limited during the growing season.

In another scenario too, splitting a sulphur application on canola can be an effective way of getting enough product on the crop without crop injury.

Cynthia Grant, a soil management and fertility scientist with Agriculture and Agri-Food Canada in Brandon, Man., says in general terms the value of a split application of nitrogen in the Black Soil zone is limited unless there are specific or seasonal circumstances.

“There are three situations where producers would consider a split application of fertilizer,” she says. “One would be to improve fertilizer efficiency. The second would be to reduce the amount of fertilizer being applied under poor growing conditions and then top up later in crop if growing conditions warranted. And the third would be to top dress later in the season in hopes of enhancing protein content.

“As a risk management tool it may be possible to improve yield or enhance protein, but every time

For top-dressing nitrogen, Guy Lafond with Agriculture and Agri-Food Canada recommends liquid nitrogen such as a UAN. You can apply this product with a liquid fertilizer applicator or with your own field sprayer equipped with fertilizer nozzles.

you make a pass over a field it costs you money, too,” she says. There is the cost of the application, of your time, and of wheel traffic, which can reduce yield where tractor or sprayer wheels have traveled.

If there is reasonable expectation of average to good growing conditions, the split application does little to improve yield compared to a single full application at time of seeding, she says.

BLACK PROBABLY NOT, BROWN MAYBE

To improve yield, the in-crop part of the split application has to be made within a 30-day window early in the growing season for the crop to benefit from the added nitrogen, says Grant. Because the requirement is so early, that is why applying everything with the seed is still the best practice in most cases. She adds that under Western Canadian growing conditions and moisture regimes, if fertilizer is banded into the soil there is little risk of nutrients being lost before it’s needed. Europe is different, she notes, which is why top-dressing is a common practice over there. European farms may have 100 days of high nutrient uptake by the crop, under often wet conditions, where nutrients can be lost from the soil during that period.

“For the most part here, nutrients that are banded into the soil at time of seeding will be there when the crop most needs it in that early part of the growing season,” she says. And research into topping up nitrogen later in the growing season to boost protein in wheat has also shown variable and limited benefit.

“Every area can experience drought at some point, but in the Black Soil Zone, under average conditions, applying recommended nutrients at time of seeding will likely be the best approach to optimize yield,” she says.

At Indian Head, Sask., Agriculture Canada scientist Guy Lafond says a split application of fertilizer can often be an effective tool for producers in the Brown Soil Zone.

“If you have very dry conditions in the Thin Black or Black Soil Zones it can be effective there too,” says Lafond. “But particularly in the Brown Soil Zone, if you have very dry conditions at seeding, why would you want to commit 100 per cent of your nitrogen up front?”

Lafond’s research has shown that applying about 66 per cent of the recommended or target fertilizer requirement at time of seeding and then topping up with the balance in-crop as conditions dictate, is a good management strategy.

“If you apply about two-thirds of the target at seeding and then have a dry growing season, you probably have sufficient nutrients to optimize yields under those conditions,” he says.

If moisture conditions change or there is a good likelihood of rain after seeding, then the balance can be applied.

WHAT TO USE, AND WHEN

Lafond recommends liquid nitrogen such as a UAN product that can be dribbled banded with a modest adjustment to most field sprayers. “You can apply it and you don’t need much rain to take it into the soil,” he says. “Even three tenths of an inch is enough to protect it.”

Farmers considering a split application do have to consider the time management issue, he says. Nitrogen in most cereal crops needs to be applied somewhere between the fifth leaf and the start of the flag leaf emergence likely in early June. In canola, nitrogen needs to be applied sometime between the start of bolting and the first flowering.

Those periods can also conflict with the timing for many herbicides.

“If someone is farming 10,000 or 15,000 acres it may be more of a time management issue,” he says. “But for producers with 2,000 or 3,000 or 4,000 acres, they are most likely able to squeeze in that top-up application.”

Saskatchewan crop consultant Darwin Kells of Elfros says he recommends to some clients to apply sulphur in a split application from other nutrients to improve canola yields.

Kells, who owns Lampton Agra Strategies, says applying about 100 pounds of sulphur fines per acre either just before, or just after seeding can help improve canola yields. “The 100 pounds isn’t an absolute figure,” he says. “It depends on soil test recommendations and should be discussed with a crop advisor. But 100 pounds of 20-0-0-24 will give you an extra 20 pounds of nitrogen as well.” He says all or most nitrogen should be applied at time of seeding.

Kells says applying 100 pounds of sulphur isn’t always practical at seeding for a couple reasons. One it could be too much nutrient and cause crop injury and secondly, it is a lot of product and depending on the seeding system could slow down the seeding operation.

While the sulphur can be applied before seeding, if you do apply it in-crop, Kells suggests it go on between stem elongation and flower stage of plant growth with a pneumatic (dry box) applicator.

Lee Hart is a field editor for Grainews in Calgary, Contact him at 403-592-1964 or by email at [email protected]

About the author

Field Editor

Lee Hart

Lee Hart is editor of Cattleman’s Corner based in Calgary.

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