Enhanced efficiency fertilizers (EEFs) are fertilizer sources or additives designed to delay or slow the release of plant-available forms of nitrogen in order to minimize losses to the environment. EEFs fall into two main categories: slow- or controlled release fertilizers, or nitrogen stabilizers (also called inhibitors).
A 2020 fertilizer use survey conducted by Stratus Ag Research found that 37.9% of Ontario corn producers and 20.5% of Ontario winter wheat producers used an EEF in their production system.
Losses of nitrogen from the field not only decrease the amount available for crop uptake but can contribute to issues with water quality and greenhouse gas emissions.
Slow- or controlled-release fertilizers
These are fertilizer products that are contain N in a form that is not immediately available for plant uptake, until specific conditions are met to release the N over a longer timeframe than standard ammonium, nitrate, or urea fertilizers.
The most common method of delaying release is through a polymer or sulphur coating to the outside of the fertilizer granule. This protective coating will weather and breakdown at a specific rate due to soil moisture and temperature, which can delay the release of large amounts of N closer to the crop’s uptake curve.
ESN® (Environmentally Smart Nitrogen) and PurYield™ are two sources of polymer coated urea available in Ontario. Best use of these products will depend on specific crop, rate, and application timing.
Nitrogen Stabilizers
Nitrogen stabilizers come in three major types:
- Urease inhibitors
- Nitrification inhibitors
- Dual inhibitors
Urease inhibitors slow down the conversion of urea to ammonium. In the presence of high pH in the soil, the ammonium can rapidly convert to ammonia (NH3) gas, which can be lost to the atmosphere through volatilization. This is especially true if the urea is at the soil surface. Urease inhibitors keep more of the N in the urea form for longer, where it’s safer from loss, until a significant (more than 0.5” or 12mm) rain can move it into the soil.
Nitrification inhibitors slow down the conversion of ammonium to nitrite and then nitrate. Nitrate is a plant-useable form of N, but is also highly mobile in the soil and can be lost in multiple ways, including:
- Leaching – downward movement of nitrate-N through the soil profile
- Denitrification – atmospheric loss of nitrate-N as nitrous oxide and nitrogen gas under anaerobic conditions (waterlogged soils)
Nitrification inhibitors keep more of the N in the ammonium form for longer, which is more stable once in the soil and still plant available.
Dual inhibitors combine urease and nitrification inhibitors to protect N in the soil from all major loss pathways. These are the most effective at reducing greenhouse gas emissions from nitrogen fertilizers as well.
Research led by Dr. Craig Drury of Agriculture and Agri-Food Canada (AAFC) in Woodslee, ON in 2013 and 2014 shows the effect of urease (UI) and nitrification inhibitors (NI) when applying nitrogen fertilizer in both a broadcast urea and injected UAN scenario:
- Adding UI+NI to broadcast urea can increase yield by 8 bu/acre and reduce NH3 losses by 75%
- Adding UI+NI to injected UAN can increase yield by 13 bu/acre and reduce NH3 losses by 90%
Table 1 lists some commonly available nitrogen stabilizers used in Ontario, along with the nitrogen products they can be used with, and the active ingredient of the inhibitor.
Table 1. Commonly nitrogen stabilizers used in Ontario.
| Product name | Used with | Active ingredient |
|---|---|---|
| Urease Inhibitors | ||
| Agrotain | UAN, urea | NBPT |
| Anvol | UAN, urea | Duromide + NBPT |
| Nitrolizer | UAN, urea | NBPT |
| SylLockUp | UAN, urea, liquid manure | NBPT |
| Nitrification Inhibitors | ||
| Centuro | Anhydrous ammonia, UAN | Pronitridine |
| eNtrench NXTGEN | UAN, urea, liquid manure | Nitrapyrin |
| N-Serve | Anhydrous ammonia | Nitrapyrin |
| SylLockDown | Anhydrous ammonia, UAN, urea, liquid manure | DCD |
| Urease + Nitrification (Dual) Inhibitors | ||
| Excelis Maxx | UAN, urea | DCD + NBPT + stimulant |
| Neon Surface | UAN, urea | DCD + NBPT |
| SuperU | Urea (pre-coated) | DCD + NBPT |
| SylLockPlus | UAN, urea, liquid manure | DCD + NBPT |
| Tribune | UAN | NBPT + Pronitridine |
References
- Stratus Ag Research. 2020. Fertilizer Use.
- Drury, C., X. Yang, W.D. Reynolds, W. Calder, T.O. Oloya, A.L. Woodley. 2017. Combining Urease and Nitrification Inhibitors with Incorporation Reduces Ammonia and Nitrous Oxide Emissions and Increases Corn Yields. Journal of Environmental Quality. 46(5): 939-949