So you've gotten back the results of the cornstalk nitrate samples collected this fall. Now, what do the results mean? The stalk nitrate test is based on the concentration of nitrate-N in the lower cornstalk (8-inch segment from 6 to 14 inches above the ground) when the plant reaches maturity (ISU Extension publication PM 1584, Cornstalk testing to evaluate nitrogen management). In general, as the amount of plant-available N in the soil during the time period before plant maturity increases, nitrate in the lower stalk increases. However, the stalk nitrate-N concentration can be greatly influenced by other external and internal plant factors.