Ammonia Loss from Unincorporated, Surface-applied Enhanced Efficiency Nitrogen Fertilizer

Research Funded by the Tennessee Soybean Promotion Board

Nutifafa Adotey, Assistant Professor and Soil and Nutrient Specialist, Sydney Logwood, Graduate Student, Lori Duncan, Assistant Professor and Row Crop Sustainability Specialist, Robert Florence, Director, Soil, Plant and Pest Center, and Ryan Blair, Extension Area Specialist III and County Standardized Trials Specialist


Ammonia volatilization from urea and Urea ammonium nitrate is recognized as one of the most common and relevant losses of nitrogen (N) in cropping systems, especially in no-till production since these fertilizers are surface-applied and unincorporated. Nitrogen loss reduces application efficiency, results in economic loss and potential environmental problems. Several strategies have been studied to minimize ammonia loss from urea, including the use of enhanced efficiency nitrogen fertilizers. Enhanced efficiency nitrogen fertilizers are modified forms of urea or UAN either by chemically or physically coating. Detailed information on EENF is available at Enhanced efficiency N fertilizer products can optimize nutrient uptake, improves crop yield, improves profitability, and reduces environmental risks. There are myriad EENF products available on the market with varying concentrations of active ingredients or formulation and UTIA’s Soil Specialist and Scientist often receive calls about the efficacy of new enhanced efficiency fertilizers.  However, evaluation of multiple products in a replicated unbiased field research is very expensive and restricted to the growing season. Furthermore, research findings suggest that the efficacy of some N stabilizers may be limited by soil type and properties. Identifying a cost effective EENF for soils in TN may optimize N uptake and reduce N loss. It is necessary to pinpoint areas susceptible to ammonia volatilization and identify products that work best for soils in Tennessee to minimize N pollution.

Materials and Method

A laboratory study was carried out to evaluate the efficacy of five EENF on ammonia volatilization applied onto the surface of 2 soils collected from producer fields. The experiment was evaluated using a precise in-lab environment-controlled system (picture below). To initiate the volatility study, the glass chambers were filled with 500 g of air‐dried soil and moistened to two‐thirds field capacity of each soil. The moistened soil is then incubated at a constant temperature of 26°C for 48 h prior to fertilizer application. At the end of incubation, N fertilizer was surface applied at an equivalent rate of 120 lbs. N a–1 based on the exposed soil surface area within the glass chambers. Ammonia from N fertilizer and soil were captured in 100 mL of 0.02 M orthophosphoric acid on 1, 2, 3, 4, 5, 6, 7, 9, 11, 13, and 16 days after fertilizer application.

Results and Discussion

Cumulative ammonia loss from the EENF products ranged from 3.3 – 10.6 and 2.2 – 16.1 % of applied N in soil 1 and soil 2, respectively. All the urea treated products were effective in reducing ammonia volatilization loss (% of applied N) by 60.6 – 87.6 and 32.3 – 91.0 % for soils 1 and 2, respectively, when compared to untreated urea. Similarly, the treated UAN reduced ammonia volatilization loss by 26.9 and 69.5 in soils 1 and 2 compared to untreated UAN. The effectiveness of the EENF treatments in both soils was: ESN® > UAN+ANVOLTM > urea+ANVOLTM > urea+Excelis® > SUPERU®. Reliable EENF products are a viable tool to reduce N losses as ammonia, regardless of the soil properties.  

NH3 loss at sampling from surface applied UAN, Urea & EENF
Cumulative NH3 loss from surface applied untreated urea, UAN, and EENF on 16DAF

Further reading