Nitrates can be absorbed quickly by plants when temperatures are low, but conversion to amino acids and protein occurs very slowly in plants during times of low temperature. Herbicides, such as 2, 4-D, tend to disrupt normal plant processes and can result in temporary high nitrate content in plants. However, spraying pastures and silage crops to control weeds actually may reduce the nitrate hazard of these feeds, especially when weeds high in nitrates are killed. Plant diseases interfere with normal growth and development. This can cause nitrate to accumulate by interfering with nitrate reduction, protein synthesis or manufacture and translocation of carbohydrates.
Plants vary in the amount of nitrate that accumulates in various tissues.
Certain weeds, such as pigweed, kochia, puncture vine and lambsquarter, often are high in nitrate. Oats and millet cut for hay at an immature stage often have high nitrate concentrations. Sorghum and sudangrasses often store high amounts of nitrates. Brome and orchard grass store very little nitrate under normal growing conditions. Legumes generally do not contain high nitrate concentrations.