Nitrates in Stressed Crops

The number one issue when thinking about when harvesting stressed crops for feed is NITRATES! When growing conditions are normal, nitrates are not a bad thing. They are the building blocks for proteins. They are absorbed by the roots and sent to the leaves where the suns’ energy (photosynthesis) turns them into proteins. However, when growing conditions are disrupted (ex, frost, drought, hail, extended cloudy periods) excess nitrate levels can accumulate. Nitrates can also accumulate in crops that are grown in soils with high levels of nitrogen fertilizer. This is typically a case in the mid-growing season when N levels have not been depleted by crop growth, or late in the season if crop growth has been delayed by cool temperatures or dry conditions. This year, we might see nitrate issues as a result of the excessively dry conditions and/or in crops with delayed growth and excess levels of N left over in the soil. After an extended dry period, moisture along with warm temperatures are needed to resume growth and convert built up nitrates into protein (>22°C is optimum). As fall temperatures drop to 10°C, growth will continue to slow and nitrates may continue to accumulate.

Since nitrate levels do not dissipate during the hay curing process, options are to wait a few days to see if temperature improves enough for growth to resume, or to cut and ensile the forage, which may reduce nitrate concentrations by 40 to 50%However, always test before you harvest your feed, because a 50% reduction in nitrates may not be safe enough to feed if original levels were extremely high. 

Some plants are more likely to accumulate nitrates, including Canada thistle, pigweed, lambsquarter, kochia, wild sunflower, smart weed, Russian thistle, oats, barley, millet, corn and sorghum-sudangrass. Perennial forages such as brome grass and alfalfa are not normally high in nitrates, but should be monitored if you planning on cutting immediately after a fall frost. Younger plants, and especially annual plants, tend to contain higher nitrate levels, but harsh growing conditions such as drought, frost and high levels of soil nitrates can lead to potential problems in all plants, including more mature plants and perennial forages. For that reason, it is always important to test all feeds after poor growing conditions. Concentrations tend to be highest in the stems, then leaves, then grain.

Some MAFRI GO offices carry small acid test kits which provide a simple "yes" or "no" answer of whether or not nitrates are present. If you’ve determined that nitrates are there, it is recommended that you wait to cut, or if you’ve already cut, have the sample sent of to a lab to determine the exact amount. With an exact level of nitrates determined, your Manitoba Agriculture, Food and Rural Initiatives Livestock Specialist can help you develop a safe ration to blend-off the high nitrate feed.

For further information, contact your GO representative.