Nitrate Accumulation in Hailed Out Crops

Hailstorms occur this time of year. Damage to annual and perennial crops can be minimal or catastrophic depending on the severity of the storm. Salvaging damaged cereal, oilseed, or hay crops after a hail event can be done safely to prevent problems with nitrate accumulation.

Nitrates change the shape of the red blood cells (hemoglobin) that carry oxygen to the tissues and carbon dioxide to the lungs. With nitrates present, the red blood cells cannot release the carbon dioxide in the lungs which reduces oxygen transfer to the tissues. Animals die or abort calves because of a lack of oxygen. Cattle are the most sensitive to nitrate poisoning. Sheep have approximately a 4 times higher tolerance than cattle. Horses being a modified ruminants do not have a problem with nitrates.

Nitrates accumulate in a plant when it is injured and is not able to convert nitrate to protein efficiently. In non-legume crops, water and nutrients are pushed into the plant from the root system at the same rate after the storm as before the hail event. Nitrate accumulates in the top leaves of the plant and concentrations peak roughly four days after the injury. If the plants recover and new growth is observed, nitrate levels can return to normal 12 to 14 days after the injury. Either cut within the first two days of the storm or wait two weeks.

Soil fertility needs to be considered when assessing plant damage and potential nitrate accumulation. In particular, the soil nitrogen content and stage of crop development are critical factors. Canola and wheat crops have the highest amounts of nitrogen fertilizer applied in the spring. If the crop is thin and not overly productive, there could be significant amounts of soil nitrogen available in the soil into August. A crop that is thick with a high yield potential would use up most of the available nitrogen much earlier in the growing season. This reduces the risk of large amounts of nitrogen remaining in the soil and less available to be transported into the plants.

Hay crops tend to have less nitrogen applied compared to annual crops. The risk of hay stands experiencing high nitrates after a hail event is much lower than an annual crop. Alfalfa and legume crops (peas, clovers, vetches) have nodules in the root system that regulate nitrate transport into the plants. The nodules only allow as much nitrogen into the plant as is needed, therefore it is extremely rare to have nitrate accumulation in legume forages

Submitting a sample to a feed testing lab for nitrate is recommended. If the sample is taken the fourth day after the storm, the results will have the highest concentration and provide a worst-case scenario. Taking the sample after the greenfeeds or silage is made is more realistic.

If the hailed crop is baled for greenfeeds and the moisture is higher than recommended, the bales can heat during the sweat phase. If bale temperatures exceed 35o C, nitrate can be converted into nitrite. This is the same breakdown process that occurs during digestion. Nitrites are ten times more toxic than nitrate. If the bales have turned brown and smell sweet or like tobacco; request an additional nitrite test. If both nitrate and nitrite are present, multiply the nitrite value by ten and then add it to the nitrate result to get the overall nitrate equivalent content in the feed.

There is information indicating that nitrates can be reduced when a salvage crop is ensiled. However, if the crop is improperly packed, not covered with plastic, or is at the wrong moisture content; fermentation will be impaired. If poor conditions exist, some nitrate reduction can occur. The quality of the silage is generally much lower. It is better to make high-quality silage and if necessary, blend it off with other feeds to reduce nitrates in the final ratio.

The size, type of animal, and stage of production all influence how much nitrate an animal can consume safely. Lactating cows and cows in the last six weeks of pregnancy are the most susceptible to nitrate poisoning. Introduce feeds slowly as it takes four to five days for the rumen microbes to adjust to the nitrates in the ration. As an example, start with 25% of the ration with the feed that contains nitrate. After 4 to 5 days, increase to 50% and continue the increases until the maximum inclusion is obtained. A secondary response occurs fourteen days after nitrates are introduced. Bone marrow produces more red blood cells which improve oxygen delivery to the tissues.

Feeding grain provides carbohydrates in the ratio which improves the process of detoxifying nitrate to nitrite to ammonia. Feeding three to four pounds per head per day is recommended. The safe feeding level for nitrates can be 1% in the final ratio for growing and pregnant animals. The safe feeding level is lower for lactating animals. Nitrate in

forage or silage can be managed so problems or difficulties are encountered during the feeding period.

More information is available from the factsheet: Nitrate Poisoning and Feeding Nitrate Feeds to Livestock. It is recommended that you consult with a feed salesperson, company nutritionist, or nutrition consultant.