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Published: 2008-05-07 00:00:00

Farmers are warned pastures recovering after the drought could be high in nitrates, posing a poisoning risk to stock.

With the drought now officially over, Environment Waikato sustainable agriculture coordinator Bala Tikkisetty is urging farmers not to pile on nitrogen fertiliser just because it has started raining.

“Understandably, farmers will be keen to speed grass growth, but it is very important to use nitrogen fertiliser carefully and test paddocks before you apply it, to protect stock health and the environment,” Mr Tikkisetty said.

Mr Tikkisetty said the drought may have caused a build up of nitrogen in some Waikato soils, and current weather conditions meant plants would have trouble converting the nitrogen to protein.

“This can result in an accumulation of nitrate in the grass, which can poison animals by stripping the blood of its oxygen-carrying capacity,” he said.

“Symptoms can include darkening of the gums and mucous membranes, diarrhea and vomiting. Sometimes death can occur so rapidly few symptoms may be apparent.”

The highest risk of nitrate poisoning is associated with young grass, especially annual ryegrasses, particularly when fed to young or pregnant stock, or stock under stress. Animals that have been underfed and then put into a paddock growing rapidly after rain are most susceptible.

“Testing herbage will give you good information about nitrate levels; your local vet should be able to provide a simple testing kit,” Mr Tikkisetty said.

He said hungry stock should never be put straight onto pasture with high nitrate levels.

“Feed them high carbohydrate supplements such as hay or silage first. Don’t let animals graze crops or pasture too hard. The highest concentration of nitrates is often found in plant parts that are closest to the soil.”

In addition, with some soils now saturated, it is much easier for surplus nitrates to leach into groundwater or run into streams and rivers, creating environmental problems.

“Colder soil temperatures greatly reduce the benefits of applying nitrogen, so if you put on more than the grass needs you will be tipping money down the drain,” Mr Tikkisetty said.

For more information or advice please call Bala Tikkisetty on 0800 800 401.