15 November 2016

Mistra Biotech study shows importance of nitrogen-efficient crops

A new barley variety that absorbs nitrogen better could reduce nitrogen leaching into watercourses and also be advantageous for the climate. This is evident from a Mistra Biotech study in which, using simulation models and life-cycle analyses, researchers investigated the effects of nitrogen-efficient crops.

Since the 1960s harvests worldwide have increased, enabling our planet to feed a growing population. One downside has been the ever larger amounts of nitrogen from fertilisers entering the soil. These nitrogen inputs rose by a factor of 7 between 1960 and 1990, exerting a range of adverse effects on the environment and climate.

Nitrogen seeps into watercourses and contributes to marine eutrophication. Moreover, a great deal of energy is required to produce nitrogen, and nitrogen inputs give rise to nitrous oxide (N2O), a potent greenhouse gas with an impact 300 times greater than carbon dioxide per unit of weight.

The nitrogen-efficient barley does not yet exist in the material world. But preparatory research — known as ‘pre-breeding’ — is under way to develop nitrogen-efficient crops. Mistra Biotech scientists are also working to develop nitrogen-efficient potato varieties.

Good for both environment and climate

The simulations and life-cycle analyses carried out by researchers at the Swedish University of Agricultural Sciences (SLU) and the Swedish Institute of Agricultural and Environmental Engineering (JTI) indicate that nitrogen-efficient barley would have a markedly positive impact in environmental and climate terms. These models, which are based on long-term field experiments, are included in the new study.

Pernilla Tidåker is one of the scientists working on the project.

‘Where there are no field experiments, we’ve used a range of different simulation models. They’ve shown us the relevance of changed characteristics to daily uptake. There’s a potential to reduce both leaching and climate impact,’ she says.

Barley is interesting, Tidåker thinks, because it is grown on a large scale in Sweden. It accounts for some 15% of the area under cultivation.

How, then, is nitrogen-efficient barley developed? One way is to breed varieties with denser, deeper root systems. Another is to strengthen the plant’s enzyme system. The result is barley that absorbs more nitrogen and reduces leaching into watercourses. And since the plant will be larger and have stronger root systems, it will bind more carbon that then, in the form of mull (humus), benefits the soil.

‘This is a new way of thinking about climate-smart crops. We’re focusing on the whole biomass, not just the small portion we use — the core. Harvest residues are an important carbon sink,’ Tidåker says.

Simulations in various soils

The scientists have studied two farming areas, one in Skåne and one in the Mälar valley. They have seen that nitrogen-efficient barley would be most beneficial in Skåne, where the soil is lighter and nitrogen leaches out more. The results were published in the October issue of the European Journal of Agronomy, and the maximum reduction in leaching found is 12%.

‘That alone doesn’t save any seas, but it can be seen as one measure along with others,’ Tidåker says.

However, there are downsides. Nitrogen-efficient crops may tempt farmers to apply even more nitrogen fertiliser to exploit the higher harvest potential. Here, Pernilla Tidåker thinks restrictions may be necessary.

‘If you introduce a crop like this to reduce the risk of nitrogen leaching, you may need to combine it with some kind of policy instrument to keep down the quantities of nitrogen applied.’

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