Nitrate Concentrations of Annual Forages Grown for Grazing in Nebraska

Annual forage samples sent by producers to Ward Laboratories Inc. for nitrate analysis were evaluated to determine which cover crop species in Nebraska are most likely to accumulate nitrates, and how often the accumulated nitrates are considered toxic by traditional recommendations. Additionally, nitrate levels of cover crop mixes grown in research trials were analyzed to ensure species differences were repeated when grown together in the same fields. Brassicas accumulate more nitrate than small grains, millet, sorghum/sudan grasses, or cover crop mixes. Brassicas accumulated levels of nitrate considered moderately to highly toxic in 48% of the samples. The other cover crop species accumulated potentially toxic nitrate levels in 20–28% of the samples. However, when cattle graze these forages, there are multiple factors that may mitigate toxicity. Cattle have grazed annual forages containing nitrate concentrations considered toxic, and no adverse health consequences were observed. More research is needed to reevaluate the risk of nitrate toxicity when grazing cover crops