Corn School: How July rains impact nitrogen leaching

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Can heavy July rains fuel nitrogen leaching and push the valuable nutrient beyond the reach of corn plant roots?

That’s a question Ontario Ministry of Agriculture, Food and Rural Affairs corn specialist Ben Rosser has been hearing a lot lately as many areas of the province have been dealt a deluge of rain.

On this episode of the RealAgriculture Corn School, we catch up with Rosser at Southwest Crop Diagnostic Days at the University of Guelph’s Ridgetown campus, where he’s conducting an experiment to measure the amount of nitrogen leaching that occurs after different levels of rain.

In the video, Rosser uses potassium chloride to demonstrate how nitrate moves in the soil after rainfall. He’s using chloride for the experiment because its movement in water is very similar to nitrate, without changing to other forms.

Rosser tests different rain event levels, ranging from zero to six inches, and measured chloride (nitrate) movement at a series of soil depth levels — from the top four inches to a depth of 20 to 24 inches. (Story continues after the video.)

As expected, the nitrates in the top four inches were reduced dramatically as the rain levels increased, but even after six inches of rain, 84 per cent of the chloride remained in the top 24 inches of the soil profile.

“Clearly we’re seeing chlorides [nitrates] move… But in this case here, even with these excessive amounts of rainfall, we weren’t getting out of that root zone, which might be three feet or 36 inches for a corn crop, on average in Ontario.”

Rosser says the experiment shows that during the growing season — June, July, August — “you really need a lot of rainfall to get that soil to saturate before it’s going to actually be able to move that [nitrate].”

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