Spring-applied anhydrous ammonia

  • When anhydrous ammonia is applied on wet soils, as is often the case in some areas now, it may not seal very well
  • It may result in more than normal soil compaction.
  • It could damage roots that enter the zone of high ammonia.
  • If soils are still cool, nitrification rates are slow, limiting the benefit of a nitrification inhibitor.

Spring-applied UAN

  • With 25% of the N in UAN as nitrate (NO3), loss potential exists starting the day of application, regardless of temperature. But this also means that N can move into the soil quickly to supply the seedlings.
  • Half the N in UAN is in the urea form, so is subject to volatilization loss (as ammonia (NH3)) assisted by the urease enzyme. Urease inhibitors (sold as Agrotain, SuperU, etc.) decrease urease activity, helping keep urea intact until it can be released in the soil, where ammonium (NH4+)  gets trapped
  • Application to cool soils slows urea volatilization, reducing the need for urease inhibitors.
  • Broadcasting UAN before final tillage is safe.
  • Broadcasting UAN right after planting is also safe as long as we don’t get a prolonged warm, dry period; a urease inhibitor might help then.
  • UAN is a good sidedress material (injected or dribbled) – keep it off the plant.
  • Little expected benefit to nitrification inhibitor at sidedress: there is little need to slow nitrification when uptake is already underway.

Urea

  • Subject to volatilization loss like UAN, but granules may limit exposure to urease. You can urease inhibitor if there’s risk; cool soils lower risk, and rainfall moves it into the soil. Spread patterns are often less consistent than UAN, may be better than anhydrous ammonia.
  • Urea can be broadcast over the crop without much damage.
  • Slow-release urea such as polymer coated and sometimes sulfur-caoted can be used to slow the release. Example: ESN
  • Release can sometimes be too slow, limiting amount of N reaching roots
  • Slow release is more appropriate for early applications than for sidedress
  • All urea materials release N to nitrate form (NH4+) first, then nitrification begins. Since nitrate is in the soil, N won’t be lost until it’s in nitrate form (NO3-).