Stalk Nitrate

The end-of-season cornstalk test is a new tool for evaluating nitrogen management practices used in any corn field in any year. The test is most valuable when used on fields that show no visual signs of N deficiency. Its use is strongly recommended for manured corn fields.

The test is based on the fact that corn plans suffering from inadequate N remove nitrate from the lower cornstalks during the grain-filling period, while corn plants that have extra N accumulate nitrate in their lower stalks during this period. Stalk nitrate-N concentrations can be divided into three categories: low, optimal, and excess

  • The low category, less then 700 ppm N, indicates high probability that greater availability of N would have resulted in higher yields. Visual signs of N deficiency are usually visible when in this range
  • The optimal category, 700 to 2000 ppm N, indicates high probability that N availability was within the range needed to maximize profits for the producer.
  • The excess category, greater then 2000 ppm N, indicates high probability that N availability was greater than when fertilizer N was applied at rates that maximize profits for producers.

Collecting the sample should be 1 to 3 weeks after black layers have formed on about 80% of the kernels of most ears. Sample the 8-inch part of the stalk found between 6-14 inches above the soil. You should collect around 12-15 samples within 10 acres of that part of the field, and store them in a dry paper bag or book so mold doesn't grow.