Tell us about the project!
This is a project that Lantmännen is running in collaboration with SLU, the University of Gothenburg and Yara during the 2023 and 2024 growing seasons. The goal of the project is todevelop a better basis for climate-smart fertilization under Swedish conditions, and to investigate the extent to which the fertilizer contributes to nitrous oxide emissions with a typical Swedish fertilization strategy in winter wheat under Nordic conditions, and whether emissions can be reduced with the help of nitrificationmore than that. 

Why is it important to reduce nitrous oxide emissions?
Nitrous oxide is a strong greenhouse gas and we need measures that reduce emissions. One cause of emissions is denitrification, which occurs when certain microorganisms in the soil use nitrate instead of oxygen in their respiration process. When the soil is saturated with water and the availability of oxygen is low, the risk of denitrification increases.  

To reduce the climate impact of nitrous oxide emissions, it is important that the mineral nitrogen we fertilize with is added based on the crop's uptake and needs. Adapted fertilization divided into several applications, which is common in Sweden, is an effective method. In other parts of Europe, methods based on the addition of so-called nitrification inhibitors, which temporarily inhibit the microorganisms responsible for the conversion of ammonium into nitrate, are common . The idea is that the plants should be given time to absorb the added nitrogen and that the concentration of nitrate in the soil should not be too high. 

Can you tell us about how you take samples?
During two growing seasons, we follow winter wheat experiments on two different soil types – clay soil and sandy soil. Measurements are taken from the first fertilization in the spring and continue after harvest and during the following winter.

And the data, how is it collected and how do you use it?
A 50x50 cm metal frame is placed on the ground surface at different stages of the experiment. Hoods are placed on the frame to collect the air, which is then sent to Yara's laboratory in Germany for analysis of the content of nitrous oxide. 

The data we collect are expected to provide answers to our questions about the effect of inhibitors on nitrous oxide emissions from the ground. The basis for our hypotheses is that we suspect that a high nitrogen utilisation is so important to limit emissions on an annual basis that any emissions that can be limited by inhibitors in the weeks after fertilization risk being evened out or exceeded by an increase in emissions during the rest of the year due to impaired nitrogen utilisation in inhibitor use due to delayed nitrification. 

2023 was the first year of the project, what is the result?  
Conditions in 2023, meanwhile, were very dry after the fertilization sessions, which meant low emissions of nitrous oxide. Later in the season, around and after the harvest period, when large amounts of precipitation fell, emissions increased. However, the effect of inhibitors is seen in the near future after the fertilization sessions, so no conclusions could be drawn about their effect. The emissions we were able to measure during autumn-winter are more attributable to the fertilization strategies rather than the effect of the inhibitors. 

Now the growing season for year two begins. Will you make any changes?
The set-up will be similar to the one for 2023 – two trial sites on two different soils. Hopefully, we will have a more favorable crop production year – all of Sweden's farmers really need that! At the same time, we will have better opportunities to study the effect of nitrification inhibitors. 

How can this project support the transition to sustainable Swedish agriculture? 
The project contributes with knowledge about how we minimize the risk of nitrous oxide emission during nitrogen fertilization. We already know today that we reduce the climate impact of nitrous oxide emissions by adding the mineral nitrogen we fertilize with based on the crop's uptake and needs. The addition of nitrification inhibitors reduces the risk of nitrous oxide release immediately after fertilization, but the risk of lower nitrogen utilization is imminent. This risks increasing nitrous oxide emissions during autumn and winter.