Forb-containing grass-clover mixtures deliver multiple ecosystem services

Inclusion of competitive forb species – chicory, caraway or plantain – in commonly practiced grass-clover mixtures is a promising strategy in intensively managed European grasslands to achieve multiple ecosystem services, such as high and stable biomass production, sustainable bioenergy production, climate change mitigation as well as improved soil biological fertility, according to scientists at Aarhus University.

Perennial grass-clover mixtures are widely adopted in arable organic farming because they can provide high biomass yield with less or no reliance on artificial nitrogen fertilizer, hence less environmental impact, meanwhile building up soil fertility that further benefits subsequent arable crops.

Including deep-rooting competitive perennial forbs will further improve productivity through more completely complementary use of resources (such as light, water and nutrients) and also promote biodiversity and associated ecosystem services. This is the theory of a group of scientists working on the MultiPlant project funded by the Green Development and Demonstration Programme (GUDP).

The MultiPlant project is in a value chain perspective to develop and demonstrate the potential of high yielding – high biodiversity - low input perennial grass-clover-forb mixtures on arable organic farms with the aim to provide both economic return and multiple ecosystem services, according to project leader Professor Jørgen Eriksen.

In previous research projects, we identified three high-yielding forbs (chicory, caraway and plantain) and found that inclusion of these forbs in mixtures improves animal nutrition through increasing mineral concentrations (such as Mg, K and Zn). With the project going on, more ecosystem services delivered by grass-clover-forb mixtures have emerged.

Plantain-containing grass-clover mixtures enhance biomass production

We found that, compared to the ryegrass-red clover mixture, inclusion of plantain in the mixture increased biomass yield by 3% to 18% (i.e. 0.2 to 2.7 t ha-1 yr-1), with the yield advantage robust across seed proportion, experimental years and slurry application. Other forb-containing mixtures (containing either chicory, caraway or all the three forbs) largely maintained the same yield as the grass-clover mixture.

Higher yields of plantain-containing mixtures are mainly attributed to positive interactions - not only between ryegrass and red clover, but also between plantain and the grass-clover mixture, which jointly contributes to more efficient resource capture and utilization.

Environmentally friendly bioenergy production from forb-containing grass-clover mixtures

Biogas production through anaerobic digestion of biomass from e.g. agricultural grasslands is one of the most common practices to produce bioenergy in Europe. The net energy balance for biogas production from forb-containing mixtures ranged between 88 and 118 GJ ha-1 year-1, which is comparable to that produced from certain energy crops. Moreover, biomass from all unfertilized forb-containing mixtures used as biogas feedstock meets the EU sustainability criteria for biofuels (i.e. 60% reduction compared to fossil diesel). Among the three forbs, plantain holds the largest potential for providing sustainable bioenergy resources with strong greenhouse gas mitigation potential.

In addition, the results showed that including plantain in the GC mixture also enhanced standing root biomass.  Greater root biomass may eventually lead to higher carbon accumulation into soil, thereby further mitigating greenhouse gas emissions.

Inclusion of caraway in grass-clover mixtures improve soil biological fertility

By sampling soils from a 3-year multispecies grassland experiment and measuring soil microbial properties and associated microbial functions, it was found that caraway-containing mixtures hosted higher microbial biomass and accelerated carbon and nitrogen cycling rate than chicory- and plantain-containing mixtures. Moreover, enhanced microbial biomass was most likely attributed to changes in root quality rather than root biomass. These results imply that inclusion of caraway in grass-clover mixtures improves soil biological fertility.

Ongoing work in the MultiPlant project is also exploring other ecosystem services, such as pollination and nitrogen fixation and subsequent residual fertility effect on the following arable crops.

Postdoc Wenfeng Cong or Professor Jørgen Eriksen
Soil fertility Section, Department of Agroecology
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Telephone: +45 8715 7874 or +4587157672

About MultiPlant

This study was supported financially by the Green Development and Demonstration Program as part of the Organic RDD-2 programme, coordinated by the International Centre for Research in Organic Food Systems (ICROFS). 

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