“A crop may still look good if there is excess or inadequate nitrogen,” said Dr. Jim Friedericks, AgSource Laboratories’ outreach and education adviser. “Even though there are no visible signs, your yield may have been impacted.”
Studies at Purdue and Iowa State University show that the nitrogen status of a corn crop can be best assessed by measuring nitrate concentrations in the lower portion of cornstalks at the end of the growing season. He noted, “Their research has proven this is a very viable tool for crop producers.”
Friedericks explained that corn stalk testing can save you money on fertilizer applications by showing fields with excess N uptake. Because of the potential positive environmental impacts, there are financial incentive programs to help pay for testing. Contact your local Natural Resources Conservation Service or local extension office for more information.
In addition to what the crop uses for growth, there are natural gains and losses for nitrogen that must be taken into account, Friedericks said. Nitrogen loss can occur due to leaching, volatilization and microbial activity, which depends on the soil temperature, oxygen, moisture and residue.
Natural nitrogen gains primarily depend on microbial activity, but there is also atmospheric fixation; rain carrying nitrogen to the soil during lightning storms can contribute up to 15 pounds of nitrogen per acre per year. Biological fixation by nodules on legumes provides nitrogen. Mineralization is microbes decomposing plant residue and organic matter to release nitrogen. Combined, they can release up to 100 pounds of nitrogen per acre per year under ideal conditions.
“Nitrogen gains can be significant,” Friedericks said. “Therefore, after forecasting the natural gains of atmospheric fixation, biological fixation, nitrification and mineralization, it is wise to plan commercial nitrogen fertilizer applications accordingly.”
“Properly identifying nutrient levels can help you make the best management decisions,” noted Friedericks. The corn stalk nitrate test shows how the N applications of the past season met crop needs. “We recommend testing the soil regularly and testing manure before it is applied in the fall because each analysis can help you better plan for next year.”
He stated that it is very important to get samples to the lab as soon after collecting them as possible.
In many areas of the upper Midwest this year, the growing season is seven to 10 days ahead of average, and you may have to test earlier than in the past.
“Take samples based on the black layer on the tip caps of the kernels, and start watching for that now," Friedericks said. “Also, testing when you wait too long and the corn is too dry, you may not get useful results.”
AgSource is a leader in agricultural and environmental laboratory analysis and information management services. A subsidiary of Cooperative Resources International, AgSource provides services to clients in the United States and across the globe. Learn more about corn stalk testing at www.agsource.com/CornStalkNitrogen.
How to sample corn stalks
When to Sample: Take samples 1-3 weeks after black layers have formed on 80 percent of the kernels of most ears.
What to Sample: Cut stalk segments eight inches long. Take stalk segments from between 6 and 14 inches above the soil. Avoid damaged stalks and remove sheaths.
Amount of Sample: Within an area not larger than 10 acres, 15 stalk segments should be randomly collected. Together, these stalks form one 'composite' sample. Areas of differing soil types or management should be sampled separately.
Shipping: Place stalks in a paper bag. Do not use plastic bags. Ship samples as soon as possible. Refrigerate if delay in shipping is one or more days. Do not freeze.