Options for reducing agricultural ammonia emissions on different soil types

A governance perspective of the European Union, that increasing efforts are dedicated towards reducing emissions of air pollutants, including ammonia. To reach this goal, Directive 2016/2284 (NEC) has been adopted, which sets a total annual emission limit value for all EU countries to be achieved by 2030. To contribute to the ambitions of sustainable agriculture, Hungary needs to reduce ammonia emissions by 32% compared to 2005 levels. Since 90% of ammonia emissions are related to agriculture, change in agrotechnical practices is needed to reach the target.

Our goal is to find optimal land use management practices in order to minimize ammonia emission, thus creating interactions between land degradation reduction and climate neutrality. A small-scale plot field trial was set up to demonstrate the possibilities of reducing ammonia emissions from urea fertilizer (46.6% active N ingredient), due to agrotechnical treatment combinations [split dose (60-40%) fertilizer application and incorporation] taking into account different test crops (wheat, triticale, grain sorghum, maize, sunflower), soil properties, climatic factors and vintage effect. In the experiment, urease inhibitor (Limus  Yellow) was tested, which was designed to inhibit the urease enzymes catalyzing the hydrolysis of urea, thus reducing and slowing the formation of ammonium, and reducing the loss of ammonia. Treatment combinations were set up in 4 replicates in a randomized design, with a total of 32 plots and 4 controls on four different soil types (Arenosol in Őrbottyán, Chernozem in Nagyhörcsök, Luvisol in Keszthely and Gleyic Chernozem in Karcag – according to WRB) with sand, loam, clayey loam and clayey loam texture, respectively. The volatilized ammonia was investigated using a passive  chamber method (phosphoric - acid  and glycerol mixture as trap to NH₃) for 6 weeks in the case of hoe culture and for 12 weeks in the case of cereals, during which the ammonia release was determined at 2-week intervals.

The inhibitor delayed the rate of ammonification in all soil types, thus reducing ammonia emissions in the weeks following application, but at a decreasing rate. The order of the soils from high to low ammonia reduction due to the inhibitor (2-year averages) was Arenosol (52%) > Chernozem (50%) > Luvisol (46%) > Gleyic Chernozem (20%), which shows a correlation with soil texture (from low to high clay content).

Split fertilizer application reduced ammonia emissions by 48% (3-year average) compared to treatments where 100% of the N dose was applied at the start (2020, 85%; 2021, 24%; 2022, 35%).

Incorporation has an ammonia emission reduction effect of 57% (3-year average) (2019, 53%; 2021, 70%; 2022, 49%). On Gleyic Chernozem, ammonia emission reduction was 68%, while on Luvisol it was 71% (2021) and 49% (2022) compared to leaving it on the surface.

Considering the test crops, incorporation was the most effective in reducing ammonia emissions in maize (62%), sunflower (67%) and grain sorghum (68%), against inhibitor effect (49, 54 and 3 %, respectively). In contrast, the inhibitor effect was the strongest in winter wheat (46 %) and triticale (52 %), against split dose application (28 and 31%, respectively).