Annual crops and weeds often have elevated nitrate levels which have to be considered when utilized in ruminant diets. Plant stress from herbicide application or diseases, 3. Plant maturity, young plants have higher nitrate levels that mature plants, 4. Fertilization, nitrates increase in plants that have been fertilized, 5. Rain increases nitrate levels particularly after a period of drought stress.
Nitrates tend to accumulate in the lower part of the plant.
Don't cut immediately after rainy period. Rain and extended cloud cover increase nitrate contents. Also, if it fits your production plans, consider ensiling the harvested forage. One certain recommendation is to have the harvested forage tested for nitrate levels. Please keep in mind that nitrate levels are lower in cured forage than standing crop, therefore nitrate tests should be done on the harvested forage as it will be fed.