Pre-Sidedress Soil Nitrate Test (PSNT) is used to determine if side dress N is needed on corn with a history of manure or sod incorporation. The PSNT measures potentially mineralizable organic N in the soil to determine the likelihood of a yield response from side dressed
PSNT’s should be run on corn fields two or more years after sod plow down where the manure rate is uncertain or may not meet the N requirements of the crop. A PSNT should also be run if N mineralization rates are expected to be higher than average (e.g., warm moist spring).
PSNT’s should not be run on corn fields that had broadcast N applications pre-plant or early post plant since nitrate picked up from broadcast fertilizer could overestimate true N mineralization potential.
PSNT’s should not be run on first year corn after a grass sod with starter N since a response to sidedressed N is very unlikely unless the soil has a very high yield potential (Hamlin, Genesee, etc).
PSNT is not needed for first year corn following an alfalfa grass mixture since a response to sidedressed N is highly unlikely.
Sampling Guidelines
- Limit sample area to < 15 acres.
- Take a separate sample for areas that are different.
a. hybrid, population, growth stage, history, management, etc. - Sample when corn is 6 – 12 inches tall.
- Wait 2-3 days after significant rainfall (due to nitrate leaching).
- Sample between rows taking care to avoid the starter band.
- Sample to a depth of 12 inches.
- Dry the sample immediately to stop mineralization.
Please include a completed copy of PSNT Sample Submission Form when submitting samples.
PSNT Interpretation
| CSNT ppm N | N available to corn plant | N Guidelines |
|---|---|---|
| <250 | Low | Not enough N available. |
| 2250-750 | Marginal | Continue CSNT testing for further evaluation. |
| 750-2,000 | Optimal | There is enough N present to support corn plant. |
| >2,000 | Excess | Corn plant had access to excessive amounts of N. If field applied with manure and/or N fertilizer, this may be cause. |
- When the PSNT is < 21.
- Add extra N if you expected to need sidedress N (i.e., field received less manure than needed to meet crop N requirement).
- Check field history & manure applications if you didn’t expect to need sidedressed N.
- Low mineralization of organic-N early in the season may be offset when warm moist soil conditions resume.
- No additional N may be needed.
- Double check N requirements and only apply extra N if needed.
- PSNT may help identify those fields that did not receive the planned for amount of manure.
- Low mineralization of organic-N early in the season may be offset when warm moist soil conditions resume.