Sampling Drought Damaged Crops for Nitrates

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July 24, 2002

With this year’s hot, dry summer and drought conditions we have received several calls regarding sampling drought damaged corn and sudan grass for nitrate. The correct sampling procedure is a very important part of any analysis that Ward Laboratories, Inc. performs and we offer the following tips:

Cut the plant samples at the height you will be swathing, cutting or the height that you expect the livestock to graze.
Pick plants that accurately represent your field. More than one sample may be necessary if various degrees of stress are evident within the field.
Cut at least 10 plants per sample.
Nitrate is highest in the lower stalk. We suggest cutting off the bottom 8-12 inches of stalk for a separate nitrate test.
Ward Laboratories, Inc. will chop and grind the sample at the laboratory.
If it rains and you are grazing the corn or sudan grass, remove the livestock immediately. The nitrate levels in the plant can increase rapidly and we recommend re-sampling to check for increased nitrates following a rain.

This summer, high levels of nitrate-nitrogen have been found in drought-damaged crops. The table below outlines animal response to nitrate-nitrogen concentration. If you have additional questions, please contact the professionals at Ward Laboratories, Inc.

Animal Response to Nitrate-Nitrogen Concentration

NO3-N ppm Comment:

Less then 1400 Safe.

1400 – 2100 Marginal, use caution when feeding. Can cause reduced milk production, abortions, and low rate of gain. It would be best to limit daily use to 1/2 of the

total daily dry matter intake.

2100 – 3000 Feeds in this range should be limited to 1/3 of the total daily dry matter intake.

3000 – 4000 Feeds in this range should be limited to 1/4 of the total daily dry matter intake.

4000 – 5000 Feeds in this range should be limited to 10-15% of the total daily dry matter intake.

Greater than 5000 Do not feed – Death may occur.