Dry Year
Wet Year
How it's calculated
The Nitrogen Efficiency factor (default 0.82) is the units of N per bushel of yield goal.
Dry year: N = Efficiency × Yield Goal − 5.1 × Nitrate
Wet year averages two adjustments:
- Efficiency × Yield Goal − 5.1 × (Nitrate + 5) — adds 5 ppm to the nitrate
- Efficiency × Yield Goal − 6.2 × Nitrate — increases the multiplier ~25%
Gallons of 28% UAN: Units N ÷ (10.67 lb/gal × 28%) = Units N ÷ 2.99
28% UAN weighs about 10.67 lb/gal and is 28% nitrogen, so each gallon supplies roughly 3.0 lb N.
Utilize Coron Metra 25B
Each gallon of Coron Metra 25B supplies the equivalent of about 12.5 units of N (often 2–3 gal/ac). The table shows the gallons of 28% UAN still needed after applying Coron, plus the estimated total product cost per acre so you can compare options.
| Coron Metra 25B | Dry — UAN needed | Dry — total cost | Wet — UAN needed | Wet — total cost |
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How to sample for PSNT
The pre-sidedress (or late-spring) soil nitrate test only works if the sample represents the field. These steps follow Iowa State and University of Minnesota Extension guidance.
- Time it right. Sample in June before sidedressing, when corn is about 6–12 inches tall (V4–V6). Don’t delay much past mid-June even if the corn is shorter.
- Sample the top foot. Pull cores to a 12-inch (0–12″) depth — that’s the zone the test is calibrated for.
- Take plenty of cores. Collect at least 12 cores from an area no larger than about 10 acres and combine them into one composite sample.
- Mind the bands. Where N or manure was banded/injected, nitrate doesn’t move sideways. Sample perpendicular to the rows at ~7.5″ spacing (for 30″ rows), starting near the row, so cores fall both in and between bands. Combine 3–4 such sets per area.
- Keep samples cool and dry them fast. Carry a cooler with ice packs to stop microbial activity, then air- or oven-dry the soil quickly (or get it to the lab right away). Warm, moist samples can change the nitrate reading before it’s measured.
- Interpret with conditions in mind. Cool, wet springs slow mineralization and can read low; use the dry- vs. wet-year results above alongside your field history and local extension thresholds.
Sources: Iowa State University Extension — Collecting Late-Spring Soil Nitrate Test Samples; University of Minnesota Extension — Tips for Accurate Pre-Sidedress Nitrate Tests; University of Minnesota Extension — What’s the right PSNT number? (2025).