Specific species can become nitrate accumulators if appropriate conditions exist. The common problem crops and weed species are presented in the following table. Crops hurt by frost or hail have a reduced photosynthetic capacity. After frost or hail, the roots are usually unaffected and are able to supply the same amount of nitrate to the upper plant as prior to the injury. The upper plant is not able to use the nitrate as efficiently and it accumulates in the stem and leaves.
Nitrate levels remain high until new tissue growth is able to utilize the nitrate that is present.
If the plant dies or is harvested, the accumulated nitrate stays in the plant material. It does not disappear with time. Nitrate levels may be reported in three different ways depending on the analytical procedure used. Be sure you know which method was used before trying to interpret the results. Refer to the following table.