Q&A: Sampling Corn Sap for Nutrient Analysis

June 12, 2015

Q: Is there any value in sampling the sap in corn to make a nutrient recommendation?

Charles Shapiro, Extension Soils Specialist: Sap analysis can be useful if there is a database that helps interpret the findings, such as the one they use in commercial potato production. It's called a petiole analysis. I don't know any research in Nebraska that correlates sap values to yield or nutrient deficiencies in corn.  I searched Google Scholar, a resource of published research, and the only related references were from the 1930s-1950s. The  American Society of Agronomy database didn't show any citations for corn sap or sap analysis.

If you want to adjust nitrogen rates mid-season, I would recommend using a calibrated crop sensor since that gives a broader view of the field since many plants are used, not a few individual plants. Anything can happen in one plant on one day, and although I am not a plant physiologist, I know that time of day is important for some nutrients and their concentration in the plant sap.

Of course, if you want to play around with sampling the sap, that would be fine, but I would not use it to generate nutrient recommendations for a lot of acres until you have some confirmation and confidence in it. I have no information on how to interpret any numbers that might be generated from a sap analysis. If anyone is recommending it, I would want to see some research that shows their system of interpretation is valid.