By Scout Nelson
The Pre-Sidedress Nitrate Test (PSNT) is a helpful tool to guide nitrogen (N) decisions in corn. New research from Minnesota now sets a reliable PSNT target of 20 ppm nitrate-N in the top 12 inches of soil during the V4–V6 growth stage. This level supports 97% of the crop’s maximum yield.
Weather plays a key role in interpreting PSNT results. In dry springs, the critical level increased slightly to 21.5 ppm, while in wet springs, it dropped to 17.4 ppm. Overall, a range of 20 ppm ± 2.5 ppm works well for most fields.
"PSNT becomes especially valuable when weather disrupts your normal N management." If you can’t apply nitrogen earlier or have heavy rain afterward, PSNT provides an in-season check to adjust plans.
When PSNT values are low, you can calculate the amount of additional nitrogen needed. Each 1 ppm below 20 means about 12.3 lbs N/acre is required. For example, a PSNT of 16 ppm is 4 ppm short. Multiply 4 by 12.3 to get 49 lbs N/acre to consider for side dressing.
However, before applying more nitrogen, consider yield potential, past field performance, and environmental factors.
To use the PSNT properly:
- Sample between V4 and V6 stages.
- Take samples down to 12 inches deep.
- Use weather history to help interpret the results.
The PSNT is most helpful when paired with local field knowledge and management experience. It gives valuable insight, especially during uncertain growing conditions.
For more detailed findings, the full study is titled Precipitation Influences Pre-Sidedress Soil Nitrate Thresholds for Corn Production. You can explore further or reach out to UMN’s nutrient management team at nutmgmt@umn.edu.
Photo Credit:gettyimages-chrisboswell
Categories: Minnesota, Crops, Corn, Energy, Weather