New measurements from SmartField show that a significant share of nitrous oxide emissions from agricultural soils occurs outside the growing season — particularly during winter thaw periods. This new knowledge will be used to establish a more accurate basis for reducing emissions.
In SmartField, emissions are measured year-round, providing a detailed picture of how nitrous oxide emissions from agricultural soils are distributed over time.
The first results based on a full year of continuous data show that emissions are not only linked to the growing season but also occur to a large extent in connection with short, intense events — especially after harvest and during winter thaw periods.
- Our first full-year measurements show that emissions occur mainly during the growing season in connection with fertilisation, in August after harvest and during thaw periods. This confirms the need for continuous measurements that can provide a more complete picture of the temporal distribution and scale of emissions. This is crucial, as large parts of the existing data basis rely on incomplete datasets, which risk underestimating total emissions, says Klaus Butterbach-Bahl, Professor and Head of Land-CRAFT, Aarhus University.
Factors affecting nitrous oxide emissions
Nitrous oxide (N2O) is approximately 265 times more potent than CO2 as a greenhouse gas and is formed when nitrogen from fertiliser and crop residues is transformed in the soil. When crops are harvested, plant residues are left on the soil surface, creating optimal conditions for microbial turnover — and thus an increased risk of nitrous oxide emissions.
In winter, weather conditions play a crucial role. When snow and ice cover the soil surface, emissions are temporarily limited. During thaw periods, nitrogen is released from frozen organic material, both because the physical conditions change and because microorganisms become active again. This can lead to intense emissions over a short period, which may account for a substantial share of the annual total. This phenomenon was observed at SmartField’s trial sites during the winter period 2025–2026.
Continuous data to pave the way for more accurate inventories
SmartField is an innovation project that combines extensive high-temporal-resolution data collection from large-scale field trials — including emissions to the atmosphere, leaching and soil and weather conditions. The data are used for modelling that maps nitrous oxide emissions from agricultural soils and identifies new opportunities to reduce them.
The full-year measurements are included as a data basis for field-level emissions modelling as part of a so-called Tier 3 model, which is intended to provide a more accurate picture than current inventory methods.
- By collecting high-temporal-resolution data from different cropping systems and scenarios, we gain a much better understanding of how nitrous oxide behaves over time and under different cultivation conditions. We now have data from the first year, but data over a longer period are needed to understand year-to-year variation, says Diego Abalos, Professor at Aarhus University.
Precise knowledge as a prerequisite for action
Today, nitrous oxide emissions are reported at Tier 1 level in the national inventories submitted to the Intergovernmental Panel on Climate Change (IPCC), meaning that a fixed share (currently 1 percent) of applied nitrogen fertiliser is estimated to be emitted as nitrous oxide. This does not reflect real-world conditions, where variation is substantial.
In SmartField, the goal is to develop a Tier 3 model, which is the most advanced inventory level. While Tier 1 uses a fixed global emission factor, a Tier 3 model integrates detailed data on soil, climate, crops and cultivation practices into process-based models — thereby providing a far more accurate picture of when, where, and under what conditions emissions occur.
- In practice, this means that we are building a robust data flow and more accurate models from field scale to national emissions inventories. Only when we have precise knowledge of when and why emissions occur can we develop targeted strategies to reduce them, explains Jørgen E. Olesen, Professor and Head of the Department of Agroecology, Aarhus University.
About SmartField
The vision of SmartField is to contribute to a documented reduction in nitrous oxide emissions from Danish agriculture of 20–30% — without negatively affecting yields and without increasing nitrogen losses to the Danish aquatic environment. The project runs through May 2029 and is funded by the Novo Nordisk Foundation.
The project is led by Danish Technological Institute in collaboration with the Land-CRAFT Pioneer Center, Aarhus University, the University of Copenhagen, Colorado State University, and SEGES Innovation.