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How can agriculture reduce nitrous oxide emissions?

With a better understanding of processes, good farming practices may be able to contribute to reducing nitrous oxide emissions from agriculture.

2018.01.09 | Janne Hansen

Timing of the various field operations in relation to each other can affect nitrous oxide emissions. Photo: Colourbox

Agriculture must contribute to fulfilling an EU decision in which Denmark is committed to reducing its emissions of greenhouse gases from sectors not already included in the emissions trading scheme by 40 percent. These sectors are agriculture, transport and buildings. 

An important source of greenhouse gas emissions from agriculture is nitrous oxide (N2O). Nitrous oxide is mainly a product of nitrogen in commercial fertilisers, animal manure and crop residues applied to the soil. Other things being equal, if the agricultural sector has to reduce nitrogen application rates in order to document efforts to reduce nitrous oxide emissions, lower crop yields could be the result. 

The question is if other things are necessarily equal, or if nitrous oxide emissions can be reduced in ways that improve nitrogen use efficiency and, in turn, crop yields. 

Nitrogen is not the only player in the field 

- An important point in this regard is that the amount of nitrogen is not the only risk factor involved in nitrous oxide emissions. Soil conditions and precipitation and, not least, application of organic matter from animal manure and plant residues also influence how much nitrous oxide is emitted from fields. Therefore, there are other measures to consider than simply reducing nitrogen application, says Senior Researcher Søren O. Petersen from the Department of Agroecology at Aarhus University.  

The most important process behind nitrous oxide emissions is denitrification. During denitrification, nitrate (NO3-) is reduced to free nitrogen (N2), but N2O is an intermediate product that can escape to the atmosphere depending on soil conditions and management. In addition to nitrate, denitrification also requires degradable organic matter and anaerobic conditions. Such conditions can develop locally in the soil around manure or plant residues, or more generally throughout the soil after rainfall. 

If these three conditions must all be fulfilled, then strategies to reduce nitrous oxide emissions may be aimed at one or more of the conditions. For example, high nitrate concentrations in the soil should be avoided in periods after manure or residue application, where degradation activity can lead to anaerobic conditions. Strategies for reducing nitrous oxide emissions thus include fertilisation and timing of field operations. Another possibility is to use nitrification inhibitors in slurry or mineral fertilisers to delay formation of nitrate.   

At the end of the day, better alignment of nitrogen availability with crop requirements can improve nitrogen use efficiency and thereby reduce the need for nitrogen fertilisation. This would benefit the farmers’ economy and the environment. 

For more information please contact: Senior Researcher Søren O. Petersen, Department of Agroecology, email: sop@agro.au.dk, telephone: +45 8715 7756, mobile: +45 2812 4304

Plantekongres, Agro, Crops, Nature, environment and climate, DCA