Nitrogen is arguably the most influential controllable yield component in most corn production systems. It is found in multiple forms in the soil, with nitrate (NO3) being the form of nitrogen most easily taken up by the plant. During the period of rapid growth and nitrogen uptake (V6-R2), to reach optimal yield the corn crop must have an adequate supply of available nitrogen in the soil every day.
One limitation of the nitrate test is the inability for the results to be used for multiple growing seasons. A nitrate test is only a snapshot of the nitrate levels in the soil at that exact moment in time. Nitrate levels can fluctuate due to water movement, denitrification, mineralization, crop uptake, and other factors.
Nitrate is generally tested as a Pre-Plant Nitrate Test (PPNT) or as a Pre-Sidedress Nitrate Test (PSNT). Both test can be used to make nitrogen application recommendations, but the PSNT, being closer to the time of rapid growth, gives a more accurate idea of how much nitrogen will be in the soil when the plant needs it.