Why are pools of nitrates in soils important?
Agricultural soils contain a lot of nitrates which represent the main source of greenhouse gas (GHG) emissions in the UK. Nitrates (NO3-) in the soil are converted into the potent greenhouse gas nitrous oxide (N2O), during a process called denitrification. Denitrification happens under oxygen limiting conditions.
Nitrates in the soil can originate from three different sources:
1. Nitrates added from fertiliser application
2. Newly formed nitrates from ammonia, and
3. Existing or ‘native’ soil nitrates.
Scientists at North Wyke are carrying out research to determine the factors controlling the utilisation of those different pools of nitrates.
To achieve this they are using a denitrification incubation system (DENIS, pictured below left) which allows them to measure directly the nitrogen-containing gases (NO, N2O and N2) by keeping soil cores (pictured below right) under a nitrogen-free atmosphere, to investigate how microorganisms utilise different soil nitrate pools as a source of available N.
The differences between nitrification (when ammonia is converted to nitrates), and denitrification are examined through looking at different soil moisture contents and varying carbon to nitrogen ratios (C:N) to determine the potential switch between the utilisation of fertiliser nitrates and native nitrates.
Go to Rothamsted’s DENIS Laboratory to find out more.
What does this mean for farmers?
Ultimately this project will lead to a better understanding of nitrous oxide emissions, improved nutrient management and possibly less reliance on fertiliser nitrates. The answer could simply be related to adding a carbon source to the soil for the ‘native’ N to be utilised by the crop.