PRODUCTION
THE WESTERN PRODUCER | WWW.PRODUCER.COM | JULY 25, 2013
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AGRONOMY | WEATHER
Did heavy rain wash away nitrogen? Severe storms | Runoff from saturated soil carries away inputs resulting in deficiencies BY REBECA KUROPATWA FREELANCE WRITER
Intense rain caused a lot of havoc in Western Canada this spring and not just from the floods that devastated southern Alberta. Many farms across the Prairies have also watched some of their inputs flush away. “Most (of the western) precipitation we’ve been receiving this year has been from thunderstorm activity and tends to be huge amounts of rain over a very short period of time,” said Doon Pauly, an Alberta Agriculture agronomy research scientist in Lethbridge. “In intense storm type of events, you get a fair amount of runoff. This year, we’d tend to see that happen in lower spots in the field, where water pools or moves. When water moves from one area of the field to another, it saturates it longer and you see denitrification where it’s yellowed. But up the slope from there, the crop is doing well.” Water that runs off or drains out rapidly also takes mobile and expensive crop inputs such as nitrogen and sulfur along with it or causes it to be lost into the atmosphere. This produces patchy crops that are starved of nutrients. Pauly said much of Alberta’s heavy rain occurred during the week of June 20. “If fertilizer was applied at seeding, around May 15, a lot of that would be converted into nitrate form, go to the surface and back up to the atmosphere as nitrous oxide or nitrogen gas,” he said. “We had a lot of the water sitting on fields in the first week of June this year, still early in the growing season. Fields need nitrogen prior to crop growth, and uptake that’s most influential on the field happens prior to the flag leaf stage. Canola likely has a slightly longer window, but that’s the stage when you get into the rapid nitrogen uptake needed to influence yield.” Precipitation in the first week of June greatly affects nitrogen deficiency and yield. Rain that occurs in the second week of July is not as worrisome because the crop has already taken up a lot of nitrogen. This year, the precipitation happened early enough that the situation could still be corrected if conditions for loss were a concern. “(However), a lot of times, conditions that cause losses also make it hard to get out onto the field again,” Pauly said. “So, you really have to weigh that, if a field operation will cause more damage to the crop. And if you go out onto the field, will you just be making an absolute mess or will you be fixing it? I don’t know anyone who’d use aerial application. It’s cost prohibitive.” The risk with fall-applied fertilizer usually occurs during the spring snow melt. Southern Alberta doesn’t receive a
lot of snow, and what does fall doesn’t stay for long. In other parts of the Prairies, snow stays all winter and then melts at one time, which increases the risk of fertilizer converting into nitrate. “When we get four-inch widespread rain over three days, the ground gets saturated,” said Pauly. “With saturated soils from long periods of rain, we have N deficiencies everywhere.” Nitrification inhibitors can be used in fall applications to kill soil organisms that convert the ammonium form of nitrogen into nitrate. “Its only temporary at the rates people use it in Canada,” said Pauly.
Saturated soil in many parts of the Prairies may be deficient in nitrogen but soggy field conditions may make it difficult to apply more. | FILE PHOTO “You’re not sterilizing your soil. You’re using that property to your advantage. Traditionally, we’ve managed it by timing and generally recommend waiting on fall fertilization until the soil has cooled down and organisms are less active. As long as you can apply late or in the fall, you shouldn’t need the inhibitor.” Pauly said environmentally smart
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nitrogen (ESN) is another good option and is not subject to nitrification if applied when seeding winter wheat. “The timing, in a lot of cases, is more critical than what you actually choose to use,” he said. “Then there’s banding, which keeps it in the ammonium form. In that concentrated band, the ammo-
nium is toxic to the bacteria.” Pauly said nitrification symptoms are similar to when a plant is dying because of a lack of nitrogen or oversaturation. “You can learn a lot by sticking a soil probe in the ground,” he said. “If you’re dealing with mud — oversaturation — it can’t be fixed with nitrogen.”