Looking to evaluate your nitrogen fertilizer program? Take a closer look at your cornstalks. End of season cornstalk testing helps give some insight into how well nitrogen fertilizer was utilized by the corn plant this year. These results won't change your yield this fall, but it is more data you can use for future management decisions concerning nitrogen application.
"Corn expresses symptoms when nitrogen is deficient," notes Steve Peterson, AgSource Laboratories vice president of laboratory services at Ellsworth, Iowa. "But there isn't a visible sign for over-fertilizing. Cornstalk testing can alert you to excess nitrogen levels and help plan for next year."
A relationship between stalk nitrate concentrations and relative yields is derived from trials. Studies at Purdue and Iowa State University show that the nitrogen status of a corn crop can be assessed by measuring nitrate concentrations in the lower portion of cornstalks at the end of the growing season.
Test tells you if corn plants had too much or too little N
Corn plants with inadequate available nitrogen remove N from lower cornstalks and leaves during the grain filling period. Corn plants with excess N accumulate nitrate in their lower stalks at the end of the season. Corn stalk N concentrations can be divided into categories for interpretation, ranging from Low/Deficient to High/Excess.
Accurate analysis is dependent on correct sampling procedures. Sample collection, preparation and shipping can influence the results. Instructions on how to take a representative sample can be found at agsource.com/CornStalkNitrogen.
How to properly sample cornstalks for nitrate testing
* When to sample: Take samples one to three weeks after black layer has formed on 80% of the kernels of most ears.
* What to sample: Cut the stalk segments 8 inches long. Take the stalk segments from between 6 and 14 inches above the soil surface in the field. Avoid sampling 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 your samples: Place the stalk samples in a paper bag. Do not use plastic bags. Ship samples as soon as possible to the lab for testing. Refrigerate them if your delay in shipping is one or more days. But do not freeze the stalk samples.
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 U.S. and across the globe. Learn more at agsource.com.