Know the risks of Nitrate poisoning and how to manage them

Know the risks of Nitrate poisoning and how to manage them

26 February 2018

Nitrate poisoning progresses fast and has no universally suitable cure. Watch for risk conditions and apply appropriate management strategies to minimise losses.

“The arrival of rain – or even a period of moist overcast days – after a long dry spell can increase the risk of nitrate poisoning affecting grazing stock,” says Ollie Knowles,Science Extension Precision Agriculture Specialist for Ballance Agri-Nutrients. “Feed and pasture with nitrate levels at 0.21% and above pose a risk. However, because of the speed at which nitrate poisoning sets in, you are better to be aware of the risk conditions in advance and take precautions rather than wait for test results.”

Farmers who suspect they have a high nitrate risk can use the following strategies:

  • Minimise stock intake of pasture in the first one to two weeks following drought-breaking rain. This requires adequate supplementary feed to cover the most at-risk period.
  • Don’t put hungry stock on high-nitrate feeds. Give them a low-nitrate feed first, preferably one that takes a while to digest (such as straw or hay) so they are less likely to gorge themselves on risky pastures and/or crops. Use in-shed feeding, feed pads or laneways, or fenced-off areas on pasture to feed out supplementary feed and reduce pasture access.
  • Dilute high-nitrate feeds with low-nitrate feeds. This helps microbes in the rumen adapt to the high nitrate levels. Adjustment can take three to four weeks.
  • Pasture nitrate levels are highest overnight and in the morning. Limit stock access to pasture at these times (or until after feeding them with a low-nitrate feed).
  • Stock lightly so animals can selectively graze and avoid hard grazing - the lower parts of stems have the highest nitrate content.
  • Provide plenty of clean drinking water for stock on high nitrate forage.
  • Use split nitrogen applications late in the season and apply nitrogen after grazing.

How it happens

Plants typically take up nitrogen from the soil as nitrate and transform most of it into ammonium and amino acids during photosynthesis – the process by which plants convert sunlight to energy for growth. “Lack of soil moisture stops nitrate uptake and it builds up in the soil,” explains Ollie.

“When rain does arrive, roots suck up the available nitrate rapidly. If cloudy days follow or if leaves are damaged by hail or frost, this reduces the plant’s ability to photosynthesise and unused nitrate accumulates in the plant. Once raised, it can take several weeks for levels to return to normal.”

When ruminants eat pasture or feed, rumen microbes convert nitrate to nitrite. “Animals can normally cope with low levels of nitrite but an excess will overwhelm the gut, resulting in nitrite entering the bloodstream.,” says Ollie.

“Once there, nitrite affects the ability of red blood cells to carry oxygen around the body – effectively ‘suffocating’ the animal.” Affected stock often stagger around as if drunk and usually die soon after symptoms appear. Young stock are more vulnerable to nitrate poisoning than older animals.

As mentioned, nitrate concentrations vary according to the age and part of the plant. Levels are generally higher in new plant growth and decrease with age. Stalks are highest in nitrate content, followed by leaves and then grain.

Different pasture or forage types also have varying nitrate levels. Brassicas are known for high nitrate levels with rape typically the highest risk. Vigorous ryegrass (especially annuals) and cereal green-feeds can also cause problems. Contrary to popular belief, the nitrate content of pasture or a crop is not reduced by using glyphosate, chopping or a frost.

For more information on nitrate mangament, talk to your local Farm Source TSR.

Article supplied by Agri-Nutrients