Corn School: Nitrogen loss and late-season impacts


A lack of late-season nitrogen and denitrification has been a concern this year, which is causing less than optimal growth in corn crops in parts of Ontario.

Matt Chapple, market agronomist at PRIDE Seeds, has been getting plenty of calls this growing season about the issue, and in this Corn School episode, Bernard Tobin joins Chapple in the field, at PRIDE Seeds’ Education Centre to talk about it.

“This particular plant, we’re seeing that firing up from the bottom, we’re at the ear leaf, we’re very pale, this if not what we would like to see, and in fact now that we’ve had pollination, we’re seeing tip-back in the plant,” says Chapple.

Earlier weather events in the growing season are playing a big part in what’s going on, says Chapple.

Side-dress nitrogen was applied early, at a good time, and the crop was growing really well, but excess moisture in the month of July caused leaching losses and denitrification, so plant-available nitrate decreased. The stress on the crop can be seen first in compacted areas, such as headlands.

Chapple says that he’d rather see denitrification and leaching loss of nitrogen early in the season because he believes soil mineralization can more than make up for those losses, which allows more time for management opportunities.

“We know that as we get farther into the growth stages, that those yield losses are irreversible,” says Chapple.

From the V6 to V10 growth stages, the corn plant can be taking up as much as one pound of nitrogen per inch of growth, and by the time the plant reaches the R stages, 80 per cent of the plant’s nitrogen has been taken up, says Chapple.

Nothing much can be done at this point of the growing season, but planning for harvest, and for next year, can help to mitigate those nitrogen losses from happening again. Chapple says to assess low-nitrogen crops before harvest — push tests as the crop progresses, or prematurely senesces, for one; acknowledging disease pressure in the future; a pinch test as the plant turns brown to determine stalk integrity; and assessing ears to calculate losses at the header.

“There’s so many great corn farmers in Ontario, and they know their soils, and they know their nitrogen strategies,” says Chapple. He suggests to get nitrogen down in starter form with the seed, to split applications, or get nitrogen down with herbicide — but to be aware of the weather and environmental conditions in order to maximize nitrogen through to grain-fill.

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