Editor’s note: The following article appeared in the Aug. 17 edition of Nutritionist e-Network, published by Dairy Herd Management. The information was provided by Rock River Laboratory, Inc., in Watertown, Wis.

Nitrate analysis is nothing new at Rock River Laboratory, Inc. However, the 2012 corn silage harvest season has brought these analysis results to the forefront, since greater than 60 percent of the U.S. has been affected by drought. 

Rock River Laboratory has gone from analyzing an average of 20 samples per week for nitrate levels to now analyzing more than 200 samples per week due to the abundance of drought-stressed corn. 

There is a silver lining, though. Based on our nitrate analysis, there has been a decline in average nitrate levels on a weekly basis over the past month. The average nitrate level from July 9 through July 13 was 918 ppm. From July 23 through July 27, the level decreased to an average of 613 ppm. Finally, Aug. 6 through Aug. 10, the average nitrate level was 560 ppm.

Below is a table that breaks down nitrate results for samples analyzed from July 2 through Aug. 10:

Total % of Samples



< 1000


1000 – 1500


1500 – 2000


2000 – 3000


3000 – 4000


> 4000




It is important to remember that a large percentage of nitrates are found in the lower portion of the stalk. If your results confirm that you have high nitrates, raising the cutting height of your corn will help to avoid some of those nitrates in your feed. Allowing the corn silage to ferment for three to four weeks may also allow the nitrate levels to drop, as fermentation causes a decrease in nitrate levels by 25 to 40 percent. Naturally occurring bacteria may be low in drought-stressed corn. Adding an inoculant is recommended to improve fermentation. However, be sure to always test the forage before feeding.

Below is a table of recommended feeding guidelines based on corn nitrate levels:

NO3-N (ppm)


< 1000

Safe to feed under all conditions

1000 -1500

Safe for non-pregnant animals; Limit to 50% of ration for pregnant animals

1500 - 2000

Limit to 50% of total dry ration

2000 - 3000

Limit to 33% of total dry ration

3000 - 4000

Limit to 25% of total dry ration

> 4000

Do not feed




When sending samples to be tested for nitrate levels, there are a few guidelines to follow to help achieve the most accurate results:

  • Avoid sending samples until five to seven days after rainfall to avoid high nitrates.
  • If you are sampling before harvest, please include three to four plants that have been cut a minimum of 6 inches from the root, or more accurately, cut at the height you plan to harvest.
  • Samples should be chopped and homogenized before being submitted. 
  • Submit the samples to the lab within 24 hours or freeze the samples before mailing. Nitrate levels can decline if kept at room temperature for even three to four hours.

Visit Rock River Laboratory's web site at www.rockriverlab.com for a current list of nitrate levels we are seeing in submitted samples. The spreadsheet can be sorted by state and county allowing you to easily find samples in your geographical region. Additional information about drought-stressed corn and nitrates can be found at the University of Wisconsin Madison Dairy Nutrition’s web site at www.uwex.edu/ces/dairynutrition. If you have any further questions regarding nitrate testing or any other of our services, please contact us at office@rockriverlab.com  or (920) 261-0446.