10/24/2021 at 10:03 AM CEST
Mixed crops capture much more CO2 than monocultures, so they can further help mitigate climate change. This is the main conclusion of an investigation carried out over seven years in an intensively managed forage system in the Lleida region of Solsonés, in the Pyrenees. Scientists conducted numerous tests in search of the perfect combination: high production and greater ability to absorb CO2 from the atmosphere. The result: mixed crops of cereals and legumes increase both productivity and net CO2 assimilation, when compared to cereal monocultures.
Forage systems, including annual and perennial forage crops, along with intensive and extensive pastures, are the main land use globally, covering approximately 30% of the earth’s surface, and representing 80% of agricultural land.
They also provide essential resources for animal nutrition. Assessing the influence of annual forage crop species on the net CO2 exchange of the ecosystem is key to developing management strategies that help mitigate climate change, while optimizing the productivity of these systems.
That was the starting point of the study, published in ‘Field Crops Research’. Until now little was known about the effect of annual forage crop species on CO2 exchange fluxes, considering separately the net CO2 balances during the growing and fallow periods, and the ecophysiological responses of the species.
Mixed crops ‘sequester’ more CO2
Mixed crops ‘sequester’ more CO2This new study evaluated the influence of cereal monocultures against mixtures of cereals and legumes in the CO2 ‘sequestration’ for the entire growing season and separately for the two growing and fallow periods. He also looked at potential CO2 exchange sensitivities related to short-term variations in light, temperature, and soil water content.
Research provides strong evidence that cereal-legume mixtures lead to higher net CO2 uptake than cereal monocultures, while respiratory fluxes (oxygen uptake) did not increase significantly.
What’s more, mixed crops favored more spontaneous regrowth during the fallow period, which was decisive for the net CO2 absorbed during the entire growing season. In general, the mixtures of cereals and legumes not only improved the net CO2 uptake capacity of the forage crop, but also ensured the productivity and quality of the forage.
The study was carried out by a research team from the Forest Science and Technology Center of Catalonia (CTFC), the University of Lleida (UdL), the Center for Ecological Research and Forest Applications (CREAF) and the Institute of Agricultural Sciences (ETH) of Zurich.
“Knowing what is the role of the species and the combinations of species of forage crops on the CO2 balance is essential to develop land management strategies that can mitigate climate change while optimizing productivity& rdquor ;, said Ángela Ribas, CREAF researcher and professor at the Autonomous University of Barcelona (UAB).
Oats and vetch, the best mix
Oats and vetch, the best mixThe article collects seven years of CO2 flux data in a system in which forage and cereal cultivation is combined with direct grazing of beef cattle after harvest (fallow period).
Already in the growing period, the mixtures of cereals and legumes showed a higher net CO2 uptake than the monoculture. The mixture between oats and vetch was the one with the highest net uptake among the analyzed mixtures. The cereal monoculture that showed the highest uptake was triticale (hybrid between wheat and rye).
At fallow period, the spontaneous regrowth of the sown species was more marked for the mixtures of cereals and legumes than for the cereal monocultures. This led to a higher net CO2 uptake after harvest, which was especially strong in the triticale, oat and vetch mix, and in the oat and vetch mix.
Cereal monocultures, on the other hand, generally did not show this regrowth during the fallow period and the gross and net CO2 capture capacity of the system decreased dramatically.
Less greenhouse gas emissions
Less greenhouse gas emissionsThe results of the research, carried out within the framework of the ‘FARRATGEM’ project, coordinated by the UdL and the CTFC, leave no room for doubt: “Cereal-legume mixtures provide enormous opportunities to mitigate climate change& rdquor ;, by reducing the emission of greenhouse gases. What’s more, they improve the fertility of the soil and allow to increase the efficiency in the use of water.
“The mixtures guarantee the cost effectiveness and the sustainability of forage holdings since the productivity is clearly favored compared to monocultures, reducing negative impacts on the environment & rdquor ;, the researchers noted.
The perfect mix of speciesAccording to these conclusions, it would be the one that combines several functional traits, with different forms of leaves, roots, uptake of resources, and so on. “It is ideal to combine legumes and cereals: the former capture atmospheric nitrogen, and the former are good competitors for light,” they concluded.
Reference report: https://www.sciencedirect.com/science/article/abs/pii/S0378429021002082
FARRATGEM project website: https://farratgem.ecofun.ctfc.cat/
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Main photo: ECOFUN