Nitrates are the most important issue when thinking about harvesting stressed crops for feed, says Glenn Friesen, a forage business development specialist with Manitoba Agriculture.
When growing conditions are normal, nitrates are not bad. The building blocks for proteins, they are absorbed by the roots and sent to the leaves where the sun’s energy turns them into proteins via photosynthesis.
However, excess nitrate levels can accumulate when growing conditions are disrupted by frost, drought, hail or extended cloudy periods.
Nitrates can also accumulate in crops that are grown in soil with high levels of nitrogen fertilizer. This is typically the case in the middle of the growing season, when nitrogen levels have not been depleted by crop growth, or late in the season if cool temperatures or dry conditions delay growth.
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This year, we might see nitrate issues as a result of excessively dry conditions or in crops with delayed growth and excess levels of nitrogen 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. Temperatures above 22 C are optimum. As fall temperatures drop to 10 C, growth will slow and nitrates may accumulate.
Because nitrate levels do not dissipate during the hay curing process, options are to wait a few days to see if temperatures improve enough for growth to resume or to cut and ensile the forage, which may reduce nitrate concentrations by 40 to 50 percent.
Always test before harvesting feed because a 50 percent reduction in nitrates may not be safe enough to feed if original levels were extremely high.
Some plants are more likely to accumulate nitrates, such as Canada thistle, pigweed, lambs quarters, 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 producers plan 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’s important to test all feed after poor growing conditions. Concentrations tend to be highest in the stems, then leaves, then grain.
Small acid test kits are available that provide a simple yes or no answer if nitrates are present. If producers have determined that nitrates are present, it’s recommended that they wait to cut, or if they have already cut, have the sample sent to a lab to determine the exact amount.
With an exact level of nitrates determined, producers can develop a safe ration to blend off the high nitrate feed.
