| | Nitrate accumulation can become a problem when crops experience light frosts, -1 °C to -2 °C for only a few hours during the night. These conditions damage the leaves of the plants but not the roots. Over the next three of four days, the roots continue to send nutrients up the plant, and the damaged plant is unable to use those nutrients, resulting in nitrate accumulation.
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"When we get a heavy frost of -5 to -6 °C for six or seven hours, the internal working system of the plant is completely destroyed and it can no longer move water or nutrients. A killing frost means that the plants are dead and therefore nitrates won't accumulate," says Barry Yaremcio, beef and forage specialist with Alberta Agriculture and Rural Development. "It's the light frosts experienced for only a few hours that damage the plant but not the internal bundles which are still able to move water and nutrients up the stem. The injured leaves can't use the nutrients effectively, and that's when there is the greatest chance of nitrate accumulate."
Annual crops are the most susceptible to nitrate accumulation, oats being the worst, but also barley and wheat. Immature salvage canola crops cut for silage or greenfeed also has a tendency for nitrate accumulation.
"Alfalfa is a legume and the nodules on the roots tend to hoard the nitrogen and only release as much as the plants require," says Yaremcio. "Nitrate accumulation is extremely rare in alfalfa.
Spring fertilizer applications also have a significant bearing on the susceptibility of the crops. High amounts of nitrogen fertilizer contribute to the possibility of nitrate accumulation.
"If fields have been used for swath grazing, winter feeding areas, have had high manure applications or high amounts of fertilizers applied in the spring, those fields are more susceptible to accumulate nitrate in the plants," says Yaremcio. "If there's been no fertilizer applied, or if it's an old grass field, those fields are not typically a problem."
After a frost, the timing for cutting the field is a key factor in managing nitrogen accumulation. "If producers can get out in the field the day after the frost and cut it as quickly as they can, there shouldn't be a problem," says Yaremcio. "Nitrate levels increase and peak at day-three to day-four after a frost."
If there is time for the plants to recover, and there is no additional frost to kill the plants, by day-14 after the frost the nitrate levels will decline and return to normal.
"It's either get out there the day after the frost and cut very quickly, or wait 10 to 14 days before cutting the field," says Yaremcio.
Contact:
Barry Yaremcio
310-FARM (3276) |
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