EEF liquid N strategies for winter wheat

Liquid UAN with an urease inhibitor in a split application optimized N use efficiency, grain protein, yield and yield stability. EEFs did not affect greenhouse gas emissions.

With the development of enhanced efficiency fertilizers (EEF), winter wheat growers have the opportunity to improve nitrogen use efficiency (NUE) and reduce greenhouse gas emissions with liquid N fertilizers.  Research was conducted to see how N source influences grain yield, protein content, and other agronomic performance under dryland and irrigated conditions, and to determine if N sources and placement impact greenhouse gas emissions.

Research was conducted over 5 years from 2013 through 2018. Irrigated sites were at Agriculture and Agri-Food Canada and Farming Smarter, Lethbridge, Alberta. Dryland sites included Lethbridge, Falher, Edmonton, and St. Albert, Alberta, and Brandon, Manitoba.

AC Flourish, a Canada Western Red Winter milling quality variety, was grown at each site with regular agronomic practices.

Soil testing was completed prior to seeding. Nitrogen fertilizer application rates were based on 80% of the recommended soil test rates. These rates ranged from 65 lbs N/ac (73 kg N/ha) to 175 lbs N/ac (196 kg N/ha) for the irrigated sites, and 55 lbs N/ac (62 kg N/ha) to 162 lbs N/ac (182 kg N/ha) for rain-fed sites.

Six different N sources were tested, and the study included a 0N control:

1) untreated granular urea (46-0-0 ),

2) untreated liquid urea ammonium nitrate (UAN; 28-0-0),

3) urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) treated UAN (Agrotain Ultra),

4) nitrification inhibitor dicyandiamide (DCD) treated UAN (Nitrapyrin; eNtrench),

5) urease inhibitor + nitrification inhibitor dicyandiamide (DCD) treated UAN (NBPT+DCD; (Agrotain Plus), and,

6) Polymer Coated Urea (PCU; Environmentally Smart N, ESN).

UAN placement used a split-applied approach with 50% of N side- or midrow- banded at seeding and 50% applied in-crop in early-spring (Feekes 4). The exceptions were PCU all side-banded at planting, and full rate of untreated urea broadcast early-spring. Broadcast liquid N used SJ3 Teejet liquid or John Deere stream nozzles.

Nitrous oxide (N2O) and methane (CH4) emissions were measured at the ‘Lethbridge Dry’ site from 2014 to 2017. These measurements took place from seeding in September to harvest in July for each treatment, and were expressed as net CO2-equivalent emissions (CO2-eq).

Highest yield with urease inhibitor-treated UAN under irrigation

Under irrigated conditions, UAN treated with a urease inhibitor (Agrotain Ultra) had the highest yield at 76 bu/ac (5.12 tonne/kg), but was statistically similar to untreated UAN at 75 bu/ac (5.06 t/ha) and the urease + nitrification inhibitor (Agrotain Plus) at 74 bu/ac (4.96 t/ha). Agrotain Ultra treated UAN was statistically higher than untreated urea by 6.4%, than the nitrification inhibitor (eNtrench) by 8% and PCU (ESN) by 14%.

Protein content under irrigated conditions were similar among all treatments ranging from 10.7 for untreated urea to 11.1 for the urease + nitrification inhibitor Agrotain Plus. Industry accepted standard is 11% grain protein content or higher.

Dryland yields were similar across many treatments with untreated UAN, untreated urea, urease inhibitor-treated UAN, and dual treated urease- plus nitrification inhibitor statistically similar at around 65 bu/ac (4.36 t/ha). Statistically, the lowest yielding were the nitrification inhibitor-treated UAN at 63 bu/ac (4.25 t/ha), and PCU at 63.8 bu/ac (4.28 t/ha) – which, agronomically, are very similar to the highest yielding treatments.

Protein content was lowest in the nitrification-inhibitor UAN (11.2%) and urease plus nitrification (11.4%) treatments. The other treatments were similar at 11.4% to 11.6%.

The researchers suggest that the combined results from irrigated and rain-fed sites in this study show that urease inhibitor-treated UAN has more potential to enhance winter wheat grain yield and agronomic performance than treating UAN with a nitrification inhibitor. This was attributed to the urease inhibitor slowing urea hydrolysis and resulting NH3 volatilization loss.

Stability analysis also found that a split-application of liquid UAN with a urease inhibitor not only improves grain yield and optimizes protein content, but also provides improved yield stability compared to the other treatments.

Greenhouse gas emissions similar

The short story is that greenhouse gas emissions were unaffected by N source at the three dryland site-years, and EEF-treated UAN was similar to untreated UAN or untreated broadcast urea. This is similar to other research that has found that the impacts of EEFs on N2O production can be limited in dryland conditions.

The researchers felt that the growth habit of winter wheat made it less responsive to EEFs effects on greenhouse gas emissions, and that the 80% N application rate may have also have helped reduce emissions.

Overall, the results show that using liquid UAN treated with an urease inhibitor in a 50-50 split application provides adequate protein, and high, stable winter wheat yield. This approach is a viable option to EEFs in granular forms for winter wheat production. And greenhouse gas emissions were not reduced in this study with the application of EEF treatments.

This project was funded through AAFC’s Growing Forward II Agri-Science Project program, which was industry-led by the Alberta Wheat Commission and leveraged funds provided by Duck’s Unlimited Canada, Alberta Wheat Commission, Saskatchewan Winter Cereals Development Commission, Winter Cereals Manitoba Inc., Nutrien, Koch Agronomic Services, and Corteva.

J.L. Owens, Z. Wang, B.W. Thomas, X. Hao, K. Coles, E. Rahmani, R. Karimi, K. Gill, and B.L. Beres. 2023. Winter wheat responses to enhanced efficiency liquid nitrogen fertilizers in the Canadian Prairies. Canadian Journal of Plant Science. OPEN ACCESS e-First

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