Storm damage to crops can result in problems with nitrate accumulations, especially if the crops were heavily fertilized in the spring to optimize yield. Nitrates are a poison that can kill ruminants. Cattle are the most susceptible to nitrate poisoning, sheep and goats less so, but still susceptible.
“The problem with nitrates is that you don’t know how high the levels are until the crop is cut and the forage has been tested,” says Barry Yaremcio, beef and forage specialist with Alberta Agriculture and Rural Development. “We’ve been getting a lot of storms… crop damage in hayfields, cereal and canola crops range from slight to severe.
“It takes about four to five days for nitrates to accumulate to peak levels in hail-damaged crops. In about six to seven days after that, or 10-12 days after the storm, if the plants are recovering from injury, the nitrate levels will return to normal and the forage should be safe to feed.”
The problem that producers experience is the balancing act between reduced yields because the leaf material dies and falls off the plant and the possible nitrates problem. Loss of leaf material results in lower feed value and tonnage per acre.
“If you can see that the leaves are drying off and you are losing yield and quality, then you need to get in and cut and silage the crop or put it up as greenfeed. In that case, it’s essential that the silage or greenfeed are tested for nitrates and that the levels are known before any is used as feed.”
Nitrate poisoning can reduce weight gains, lower milk production, depress appetite, cause abortions to occur in early pregnancy or in the last month of gestation and increase the susceptibility to infections. These problems or losses are not often readily recognized and will occur when nitrate levels are at 0.5 to 1.0 per cent of the feed consumed (on a dry basis).
“It comes down to a management decision,” says Yaremcio. “If you’ve had to cut a field in that four to five days after a hailstorm, take representative samples of the silage or greenfeed and get it tested. Knowing what the levels are is absolutely necessary to determine how to mix off the feed and develop a feeding program so you don’t run into trouble with nitrates and lose animals or have cows abort.”