FACTOR
1: What N product was used?
| Anhydrous ammonia with N-Serve | 2 points |
| Anhydrous Ammonia | 3 points |
| Other fertilizer banded | 4 points |
| Other fertilizer broadcasted | 5 points |
FACTOR
2: When was the fertilizer N applied?
| After April 20 | 3 points |
| Before April 20 | 5 points |
FACTOR
3: What has been the predominate soil moisture status in the field this spring?
| Normal soil conditions | 1 point |
| Wet soils | 3 points |
| Standing water/saturated soils | 4 points |
FACTOR
4: What is the crop's current condition?
| Green plants > 12" tall | 1 point |
| Green plants < 12" tall | 2 points |
| Chlorotic plants < 12" tall | 3 points |
| Chlorotic plants > 12" tall | 5 points |
Total
the score for the four factors and use the following guidelines:
| Less than 11 | No supplemental N recommended |
| 11-16 | Evaluate again in 4-7 days |
| 17 or more | Add an additional 40-70 lbs. N/acre |
The "re-evaluation" option is only viable until you no longer can sidedress. While a total score of 17-18 may merit 40 lb/acre N, a score of more than 18 may require higher rates. However, Illinois research has found that 50 lb N/acre was satisfactory for a wide range of conditions. Keep in mind that good judgment is still important when using various methods to estimate N needs. Also, each field needs to be evaluated individually.
Producers that have applied manure to their fields should consider the PSNT as a nitrogen management tool for corn production. This test estimates the level of nitrate-nitrogen in a field and is adapted to a sidedress program. Samples should be collected 5 to 10 days prior to time of sidedress. The optimum time for sidedress is between the V4 to V6 growth stage (4th and 6th -collared leaf, respectively). The depth of core samples should be 12 inches and removed from 15 to 20 sites across a uniform area no larger than 20 acres. Samples should be dried, or at least, not sent to laboratories in plastic bags. Lab selection should be based on accuracy and timeliness (receiving samples and reporting results). If the results are in excess of 30 ppm, adequate nitrogen should be available for this year's corn crop. If it is less than 15 ppm, the normal nitrogen rate should be applied. Between 15 and 30 ppm, other factors should be considered before reduction of the normal nitrogen rate.
Research from Ohio State University has shown that in most situations, normal nitrogen rates are required at values less than 30 ppm. The test only measures nitrate-nitrogen. If samples are collected too soon, ammonium nitrogen may have not converted to the nitrate form. Some labs include the ammonium value. This value may be used to confirm the conversion (or lack of conversion) of ammonium-nitrogen to nitrate-nitrogen. However, only use the nitrate value for management decisions. Test results may not be useful if heavy rains or several days of soil saturation occur between date of sampling and reporting of results. In summary, the pre-sidedress nitrogen test has been a useful management tool for manured-fields, and occasionally useful for fields with cover crops. In some cases, it may assist in estimating nitrogen losses from early preplant nitrogen.