The author is a University of Vermont agronomist and nutrient management specialist.

The pre-sidedress nitrate test (PSNT) uses a soil nitrate measurement to predict the need for sidedress-N on corn. The sidedress-nitrogen (N) recommendation is based on research that correlates soil nitrate concentrations at the time corn is 8 to 12 inches tall with the total amount of plant-available nitrogen that will be released to the growing crop by soil organic matter over the course of the growing season. It gives good recommendations in a normal year but struggles when conditions are abnormal.

The PSNT suffers a low adoption rate, probably because it:

• needs to be done during an otherwise busy time of year
  
• requires that samples be taken to a depth of 12 inches, which can be challenging
  
• does not always demonstrate a payoff within a week

There is a newer approach: Adapt-N

Cornell soil scientists have developed a program (Adapt-N) that models nitrogen behavior in agronomic soils and generates a sidedress N recommendation based on a set of relevant soil variables including historical and real-time weather data.

How did the PSNT compare with Adapt-N?

The PSNT consistently over-recommended sidedress N by about 30 to 50 pounds per acre on the fields we studied in 2013.

There are several practical reasons that Adapt-N will typically be much better than the PSNT for predicting the need for sidedress-N in corn:

• Adapt-N accounts for most major variables known to affect soil nitrogen behavior.
  
• Adapt-N has the ability to model behavior of soil N under variable environmental conditions.
  
• Adapt-N uses historical and real-time data to model how much plant-available nitrogen is in the ‘pipeline' and anticipate when it will become available to the crop.
  
• If managed well, Adapt-N can and will continue to improve in accuracy over time.
  
• Data can be entered into the Adapt-N program at any time: early in the spring, at night, or on rainy days.
  
• Adapt-N allows the user to subdivide fields into more appropriate management zones with little extra effort.

While Cornell maintains control over the evolution of the tool, Adapt-N has been licensed to Agronomic Technology Group and will cost about $2 to 3 per acre this year.

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