Commercial Agriculture Program
Fall 2009
The Missouri Corn Stalk Nitrate Test Challenge
By John Lory, Division of Plant Sciences and Commercial Agriculture Program
Did you do a good job predicting nitrogen need for your corn crop last spring? Did you over apply? Under apply? Or get your rates just right? The stalk nitrate test is a powerful tool for assessing the fertilizer nitrogen decisions in a corn field.
Research from Iowa and other states has calibrated nitrate concentration in the corn stalk with the nitrogen status of the harvested corn crop. Nitrate concentrations above 2000 parts per million are indicative of a crop that had excess nitrogen; nitrate concentrations below 700 parts per million are indicative of plants that had marginal nitrogen supply (250-700 parts per million) or were clearly nitrogen deficient (<250 parts per million).
How to sample fields
- The optimum window of opportunity for collecting samples is from ¼ milk stage to up to three weeks after black layer formation.
- Use a set of hand shears or loppers to remove an eight-inch segment of corn stalk from the corn plant. The top cut should be 14 inches above the ground; the bottom cut six inches above the ground.
- Get a stalk segment from at least 15 randomly selected plants from the field or subfield you are sampling
- Place the samples in a paper bag for shipping to the lab for analysis. Do not freeze the sample. Samples held more than 24 hours before shipping should be refrigerated.
Many fields will be past the optimum sampling window when this article is published in mid October. You can sample fields past three weeks after black layer if there has not been a large rainfall event that could leach nitrate out of the stalks after harvest.
Also, if you are cutting stalks after harvest, be sure you are still removing a section starting six inches above the ground and providing an eightinch sample. A sample from closer to the ground will give an artificially high reading.
The Missouri Corn Stalk Nitrate Test Challenge
My program is working with the University of Missouri Soil Testing Laboratory to promote use of this test in Missouri. Typical analysis cost for the test is $12 per sample. We will analyze up to 10 samples from any Missouri farm at the MU lab at no cost if you submit the requested information on the form when you submit the sample.
Send samples to Attention Stalk Nitrate Test Challenge, 23 Mumford Hall, University of Missouri Soil Testing Lab, Columbia, MO 65211 or MU Delta Regional Soil Testing Lab, 147 State Hwy T, Portageville. MO 63873.
Visit the Corn Stalk Nitrate Challenge website at http://nmplanner.missouri.edu/tools/Stalk_Nitrate_Challenge.asp for more information and to download copies of the reporting form. Phone Shane Ferguson at 573 884-6311 to have a form(s) mailed to your home.