Fertilizer nitrogen (N) is a major input for crop production in Ontario. However, nitrogen use efficiency (NUE) in the farmlands is low, as only about 40-65% of the total applied fertilizer N is recovered in crops. Nitrogen fertilizers that are not taken up by the crop can either be immobilized by microbes or vulnerable to losses as ammonia (NH3), nitrate (NO3−N), nitrous oxide (N2O), and di-nitrogen (N2). Losses of N can contaminate water bodies, release potent greenhouse gas (e.g., N2O) and create particulate aerosols (e.g., NH3) that impact human health.
There are various enhanced nitrogen products developed with the objective of reducing N losses and to improve crop N use efficiency in field and horticultural crops. Those Enhanced Nitrogen Fertilizers are mainly divided into two groups.
- Enhanced Efficiency Fertilizers (EEF): are forms of N fertilizers that include additives, physical barriers or different chemical formulations that control fertilizer release or alter reactions. This category is further divided into two groups:
- Slow-release fertilizers are low soluble and more complex than regular fertilizers that usually requires microbial degradation to release plant available N. Examples are Urea Formaldehyde (35% cold water insoluble N and 38% total N) and Methylene Urea (40% N of which 60% is water soluble).
- Controlled release fertilizers are granulated fertilizers coated with other additives (e.g., polymer, sulphur, etc.) that releases nutrients gradually into the soil in a controlled way. Examples are Sulphur coated Urea (30-40% N) and Polymer coated urea (18-44% N). Environmentally Smart N which we call ESN with 44%N, is an example of polymer coated urea that is designed to slow down the rate of N release to better match the crop demand than conventional urea.
- Stabilized Fertilizers (SF): Fertilizer products in which inhibitors are added to the fertilizers to retard bacterial or enzymatic activities in the soil. Examples are:
- Nitrification inhibitors (NIs): They retard bacterial oxidation of ammonium to nitrate by nitrosomonas and nitrobactor. They maintain ammonium in the ammonical form to prevent nitrate leaching and nitrous oxide emissions.
- Ureas inhibitors (UIs): They slow the conversion of urea to ammonium by ureas enzyme. The UIs are used only in conjuction with Urea fertilizers mainly to decrease volatilization loss from surface application of Urea fertilizers.
It is important to note that soil conditions (e.g., temperature, moisture content and osmotic potential) may influence N release from enhanced N fertilizers. In general, N release is positively correlated with soil temperature and moisture. Enhanced Efficiency Fertilizers will be most effective in seasons where N loss from the soil may be high due to high rainfall, light soil texture and low organic matter content.
In terms of cost, enhanced N fertilizers provide additional value or benefits to the fertilizer and thus they are expensive than regular fertilizers. Also, even within enhanced N fertilizers, Enhanced Efficiency Fertilizers (EEFs) may cost more than Stabilized Fertilizers (SFs). Even within Enhanced Efficiency Fertilizers, slow-release fertilizers have price similar or higher than controlled release fertilizers. Most recent studies in central and eastern Canada have indicated that the cost of enhanced N fertilizers can be offset by reduce N rates because of lower losses (more of a sure thing) and/or higher yields (not clear a sure thing).
Carson, L.C. and Ozores-Hampton, M. 2014. Description of Enhanced-Efficiency Fertilizers for Use in Vegetable Production (Online). HS1247/HS1247: Description of Enhanced-Efficiency Fertilizers for Use in Vegetable Production (ufl.edu).
Mezbahuddin, S., Spiess, D., Hildebrand, D., Kryzanowski, L., Itenfisu, D., Goddard, T., Iqbal, J. and Grant, R. (2020). Assessing Effects of Agronomic Nitrogen Management on Crop Nitrogen Use and Nitrogen Losses in the Western Canadian Prairies. Front. Sustain. Food Syst. 4:512292. doi: 10.3389/fsufs.2020.512292
Soil Fertility Specialist, OMAFRA