Heavy Rains, Nutrient Losses and the Case for "Variable Source" Nitrogen

Excess water after heavy rains in parts of Western Canada is not only impairing plant growth through oxygen deficiency, but it’s also causing significant nitrogen losses.

As John Heard, soil fertility specialist with Manitoba Agriculture, explains in this video, N losses depend on soil type, with rain causing leaching in sandier soils and more denitrification in clay areas.

“We’ve had rain causing both measures of losses,” he says, referring to a diagram of the nitrogen cycle. “Where we have standing water, our major loss is denitrification.”

In spring, when soils are cool, he says the rule of thumb for Manitoba is that 2 to 4 pounds of nitrogen per acre are lost each day to denitrification.

“But now that we have 20 degree soil temperatures, we’ll lose three-fold that. Maybe 8 to 16 pounds per day,” says Heard.

How this will impact the crop depends on crop type. Canola and wheat take up most of their nitrogen earlier in the growing season, while most of the nitrogen demand for corn and soybeans occurs in July and August.

Enhanced efficiency nitrogen fertilizers are beneficial in these wet conditions, he explains, as they slow the conversion of ammonium into nitrate — the form which is at risk of denitrification and leaching.

While growers may not be interested in applying these stabilized nitrogen products across an entire field, Heard suggests possibly moving to “variable source” nitrogen if equipment is capable of applying more than one product.

“When you move to lower landscapes or sandy ridges, then products that tend to stabilize nitrogen in ammonium form or control the release may have a particular advantage,” he says.

Check out the video above, filmed at Manitoba Crop Diagnostic School in Carman on July 14, for more on the nutrient impact of heavy rains and strategies for minimizing nitrogen losses.

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