Forbs enhance productivity of unfertilised grass-clover leys and support low-carbon bioenergy

Abstract

Intensively managed grasslands are dominated by highly productive grass-clover mixtures. Increasing crop diversity by inclusion of competitive forbs may enhance biomass production and sustainable biofuel production. Here we examined if one or all of three forbs (chicory, Cichorium intybus L.; caraway, Carum carvi L.; plantain, Plantago lanceolata L.) included in ryegrass-red clover mixtures enhanced above- and below-ground productivity, and assessed their biofuel potentials, based on a three-year experiment with and without fertilisation as cattle slurry. We determined herbage yield, standing root biomass, and estimated methane energy output and greenhouse gas (GHG) emissions per energy unit using life cycle assessment. Results showed that plantain-containing grass-clover mixtures significantly increased herbage yield, while chicory- or caraway-containing mixtures maintained similar yields to the grass-clover mixture. Standing root biomass of the grass-clover mixture was enhanced by inclusion of caraway and plantain, with that of plantain further enhanced by fertilisation. The highest methane energy output was achieved in plantain-containing grass-clover mixtures. All unfertilised mixtures achieved the 60% reduction in GHG emissions compared to fossil fuel, whereas all fertilised mixtures did not meet the 60% reduction target. These findings suggest that including competitive forbs such as plantain in grass-clover mixtures enhances productivity, supporting low-carbon footprint bioenergy production.

Soil nutrient levels define herbage yield but not root biomass in a multispecies grass-legume ley

“…Previous work showed that root biomass of grass- Table 1 Fertiliser history of the Askov LTE. The rate (kg ha −1 yr -1 ) of total nitrogen (N), phosphorus (P) and potassium (K) added in 1 A M (animal manure) and 1 NPK (mineral fertiliser) from 1973 to 2016. legume ley was substantially higher on rows than between rows (Cong et al, 2017) wherefore we quantified root biomass separately for onrow areas and between-row areas. Then whole-plot root biomass was the weighted sum of root biomass in the two areas.…”

“…The row distance of grass-legume ley was 12 cm, dividing the plot area into stripes each comprising 6 cm-wide on-row area and 6 cm-wide between-row area. Six random cores were taken in the on-row area and another three in the between-row area to account for the higher variation in the on-row area (Cong et al, 2017). In total, we collected 180 cores (20 plots × 9 cores).…”

Forbs differentially affect soil microbial community composition and functions in unfertilized ryegrass-red clover leys

“…Inclusion of plantain significantly enhanced herbage yield of the reference mixture, while the same pattern was also observed for root biomass (see Fig. 4 in Cong et al, 2017). Surprisingly, neither herbage yield nor root biomass significantly correlated with any of soil chemical or microbial variables, except for a positive correlation between herbage yield and k (Table 3).…”

Short‐term residual N unaffected by forbs in grass‐clover mixtures

“…The grasslands, established in spring 2013 in a long-term organic dairy crop rotation on loamy sand (Eriksen et al, 2015), were composed of red clover (Trifolium pratense L., variety Rajah), perennial ryegrass (Lolium perenne L., variety Stefani), chicory (Cichorium intybus L., variety Spadona), ribwort plantain (Plantago lanceolata L., wild type) and caraway (Carum carvi L., variety Volhouden) in different seeding mixtures (Table 1) and managed as described in Cong et al (2017). The resultant swards varied in red clover proportion, input of N from N 2 -fixation (246-617 kg N/ha), and N balance (À54 to 137 kg N/ha) depending on species composition in the seed mixtures (Table 1).…”

“…Recently, nonlegume forbs have been included in grassclover mixtures to improve mineral nutrition for grazing animals from the forage (Pirhofer-Walzl et al, 2011), plant diversity and herbage production (Cong et al, 2017). In grasslands, legume biomass is an indicator of N released to the subsequent crop (Vrignon-Brenas et al, 2016); hence, inclusion of nonlegume forbs could affect the residual N fertility due to their replacement of N-rich legumes in the sward.…”