Scientists hope to store carbon in soil in the future, to help battle climate change, but doing so could release another greenhouse gas, nitrous oxide.
New research shows that poorly-drained agricultural soils emit enough nitrous oxide that the resulting climate change effects could far exceed the benefits of using the same soil to store carbon.
Nitrous oxide has 298 times the warming potential of carbon dioxide (CO2) over 100 years, according to previous research.
Soil carbon sequestration is a process in which CO2 is removed from the atmosphere and stored in the soil carbon pool largely mediated by plants through photosynthesis, with carbon stored in the form of SOC (soil organic carbon).
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The study, published on Monday in academic journal Proceedings of the National Academy of Sciences, found that a range of agricultural soils produce nitrous oxide emissions in quantities big enough to contribute to climate change.
Steven Hall, an associate professor of ecology, evolution and organismal biology at Iowa State University (ISU), said: "In this study, we show that the climate warming effects of nitrous oxide emissions from local corn and soybean soils are two-fold greater than the climate cooling that might be achieved by increasing soil carbon storage with common agricultural practices."
Scientists, farmers and policymakers are considering strategies that might encourage producers to store carbon, also a greenhouse gas, in the soil, where it can't contribute to climate change.
The new research indicates that any such policies should first take into account nitrous oxide emissions, Hall said.
Failure to do so could result in policies that are much less effective in addressing climate change.
Instead, Hall said management plans also should encourage nitrous oxide mitigation strategies in concert with carbon sequestration.
New products known as enhanced efficiency fertilisers, as well as the application of biochar to fields, might also help to limit nitrous oxide emissions.
Microorganisms in the soil give off nitrous oxide as a byproduct as they cycle nitrogen. Nitrogen stimulates nitrous oxide production, so adding nitrogen fertilisers to soil tends to result in more emissions.
"If we want to maximise our climate benefit, we want to be strategic about it," Hall said.
"We're not simply going to flip the switch on climate just by putting more carbon in the soil. Nitrous oxide emissions need to be a priority as well."
Hall and his fellow researchers used small containers placed at various locations on top of the soil of ISU research farms in central Iowa.
The containers pump air samples into a central shed where an analyser automatically measures nitrous oxide content.
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