Agronomy Update
Agronomy update: Reduced emissions with EEF fertilizer but little agronomic benefit

Nitrous oxide (N2O) is a major greenhouse gas (GHG), and Canada has set a target to reduce N2O emissions associated with fertilizer application by 30 per cent below 2020 levels by 2030. The use of enhanced efficiency fertilizers (EEF) could be one tool to help reduce emissions as part of a 4R nutrient stewardship framework.

Research was conducted by the University of Manitoba to investigate whether placement and depth of granular urea or an EEF product affect N2O emissions and yield for canola production in Manitoba. Field trials were conducted in southern Manitoba over three years from 2014 to 2016. There were two sites per year at Carman and Kelburn in 2014, Carman and Oak Bluff in 2015 and Brunkild and Domain in 2016.

Fields had soybean grown the previous year and were chosen because of low carryover soil nitrate-N resulting in greater potential yield response to nitrogen (N) fertilizer. Canola was seeded on eight-inch (20 cm) rows at one-half inch (1.3 cm) depth. Phosphorus, potassium and sulfur fertilizers were applied according to soil test recommendations as a pre-plant broadcast/incorporated treatment.

Nitrogen fertilizer placement treatments included broadcast/incorporated, shallow banded and deep banded fertilizer. Broadcast N was incorporated to a six-inch (15 cm) depth with a rotary tiller. Shallow banded placement was 0.75 to one inch (two to 2.5 cm), and the deep banded placement ranged from 1.6 to four inches (four to 10 cm) depths depending on the site. Banded treatments were applied with a mid-row disk bander.

Untreated urea and SuperU (46 per cent N), a commercially available granular urea product containing a urease inhibitor and a nitrification inhibitor, were compared.

Nitrogen fertilizer rates were 70 and 100 per cent N supply based on soil test recommendations. The target grain yield was 53.5 bushels per acre (three tonnes/ha). There was also a zero N fertilizer control at each site.

Canola yield and nitrogen recovery efficiency (NRE) were calculated. Nitrous oxide emissions were measured for the treatments receiving 100 per cent N from planting to freeze-up at one to three times per week. Daily and cumulative emissions were calculated. Yield-based N2O emission intensity (EI) for each treatment was calculated.

Few differences in canola yield
Overall yields were comparable to commercial fields in the area, excluding Carman 2015 which had low yield because of poor germination. Two of the sites had yields higher than the 53 bu/ac target, and four were lower.

Yield increases over the control were observed at five of six site-years at the 100 per cent recommended N rate, and there were few yield differences in fertilizer source or placement. This indicated that SuperU offered few agronomic benefits in this trial.

Fertilizer nitrogen recovery efficiency was not affected by N treatments at any site at the 100 per cent N rate.

There were spikes in daily emissions coinciding with heavy rainfall events. At site years with lower rainfall, shallow and/or deep band N had reduced N2O emissions but had higher emissions at site-years with more rainfall after seeding. Under these wetter conditions, N2O production could have more readily occurred from the concentrated bands in the shallow and deep banded treatments compared to the more dispersed N fertilizer in the broadcast/incorporated treatment. Even though there were higher N2O emissions under wetter conditions, banding N tended to increase yield and fertilizer recovery, implying N2O emission losses were too small to reduce N availability, uptake or yield.

At four of six site-years, SuperU reduced N2O emissions by 30 to 57 per cent compared to conventional urea, for all placement methods. Since reductions were observed for all placement methods, the researchers felt that delayed nitrification was the reason for the reductions. They indicated SuperU was effective in retaining soil N in the NH4+ form longer and therefore provided more opportunities for crops to take up NH4+ and reduce losses through N2O emissions.

Shallow banded N at 0.75 to one inch had higher emissions than broadcast/incorporated or deep banded N. This occurred across all six site-years. The researchers indicated that since there wasn’t an agronomic benefit to shallow band over other placement methods, it should be avoided otherwise N2O emissions may increase.

The overall results showed urea treated with a dual inhibitor such as SuperU can reduce N2O emissions in canola production in southern Manitoba. However, little agronomic benefit was observed with similar yields between SuperU and untreated urea. The additional costs of EEF without a corresponding economic benefit remain a barrier to their adoption unless the cost is shared by society. 

Bruce Barker divides his time between CanadianAgronomist.ca and as Western Field Editor for Top Crop Manager. CanadianAgronomist.ca translates research into agronomic knowledge that agronomists and farmers can use to grow better crops. Read the full Research Insight at CanadianAgronomist.ca.