By George Silva
The end of season corn stalk nitrate test is one of the few diagnostic tools available to determine if excess nitrogen was applied to corn. The methodology and interpretation of this test were highlighted in previous Michigan State University Extension articles: “End of season corn stalk nitrate test” and “End of season cornstalk nitrate test in a drought year.”
Here are some tips to the correct sampling procedure that is critical to getting reliable data from this test.
- The time for stalk sampling is critical. It is two to three weeks after physiological maturity or when black layers have formed on about 80-90 percent of the kernels. At this stage, any further mobilization of nitrogen from the plant to the kernels has ceased. Typically, most leaves and stalks have turned brown at this stage.
- The portion sampled is the 8-inch segment of stalk between 6 and 14 inches above the soil.
- Collect 12-15 segments within an area no larger than 10 acres.
- Remove all the leaf sheaths from the segment.
- The sample needs to be taken at random, but any plant with stalk rot should be discarded. The rot destroys the pith area of the stalk, rendering it dark brown to black. Notice the color of healthy stalks in the photo.
- Plants adjoining a skip should be avoided.
- Areas with different soil types or management histories (manure practices and previous legume crops such as alfalfa and clover) should be sampled separately.
- Hybrids with different maturities and widely different planting dates may require different sampling dates.
- Place samples in paper (not plastic) bags to allow some drying and minimize mold growth. Send to a laboratory as soon as possible. Refrigerate samples (do not freeze) if stored for more than a day before mailing.
Source: msu.edu