Clover in agriculture: combined benefits for bees, environment, and farmer

Abstract

Concerns over the increasing cost and environmental impact of high inorganic nitrogen (N) inputs have led to a reappraisal of the role of legumes, particularly clover, in maintaining soil fertility in improved grasslands. Clover and other legumes host the symbiotic root bacteria Rhizobium that fix N, reducing the need for N fertiliser application. Grass plus clover swards are comparable to grass monocultures given medium to high inorganic N inputs in terms of companion grass growth, livestock performance and, yield of subsequently planted crops. Reduced N fertiliser input also reduces associated N leaching into water and greenhouse gas emissions during manufacture, transport, and application. In addition, increased use of clover in grasslands also benefit flower-visiting insects by providing an abundant source of nectar and pollen in summer. This is a critical period due to high levels of competition for these in summer. Because temporary and improved grassland covers almost half (47%) of UK land area this habitat type has great potential in wildlife conservation. Further research is needed on the agronomic and conservation benefits of more diverse swards, as incorporation of additional forb species may complement clovers and legumes to benefit a wider range of flower-visiting insect species. In addition, more information on the attitudes of farmers for or against using clover and legumes in grasslands is needed, as they make the management decisions for most agricultural land in the UK. Implications for insect conservation: increased use of clover is a low-cost way to improve the food supply for flower-visiting insects, while to sustaining agricultural productivity and reducing environmental impact.

Improving pollen and nectar supply by identifying the red clover (Trifolium pratense) cultivars that attract most pollinators

“…One result of greater agricultural intensity has been the reduction of floral resources, primarily pollen and nectar, which is considered a primary cause of pollinator decline (Baude et al, 2016; Biesmeijer et al, 2006; Carvell et al, 2006; Ollerton et al, 2014; Potts et al, 2010). A benefit, therefore, of increased use of red clover in agriculture is greater floral resources for pollinators during bloom, providing a potential ‘win‐win’ for farmers and pollinators (Harris & Ratnieks, 2021). Red clover is an important source of floral resources for bumblebees in the UK and Europe, including declining species (Carvell et al, 2006; Goulson et al, 2005; Rundlöf et al, 2014).…”

“…Thirteen accessions tested were diploid (2n = 2x = 14), which is the natural ploidy level of red clover, and seven tetraploid (2n = 4x = 28), which is induced to improve persistence and forage yield (Boller et al, 2010), and differences among accessions within and between these ploidy levels were examined. These results will help plant breeders and farmers to ‘make the most’ of red clover by increasing its value to pollinators (Harris & Ratnieks, 2021).…”

Phenological imbalance in the supply and demand of floral resources: Half the pollen and nectar produced by the main autumn food source, Hedera helix, is uncollected by insects

“…For example, removal of non-productive habitat such as hedgerows and semi-natural habitats (Blackstock et al, 1999;Petit et al, 2003;Ratcliffe, 1984), replacement of hay meadows with intensely managed pastures (Fitzpatrick et al, 2007;Green & Stowe, 1993), simplification of crop rotations (Harris & Ratnieks, 2021;Ollerton et al, 2014), and increased use of fertilisers and herbicides (Ollerton et al, 2014).…”

“…In agricultural landscapes, which is c.70% of UK land area (DEFRA, 2020a), many changes resulting from intensification have reduced floral resources. For example, removal of non‐productive habitat such as hedgerows and semi‐natural habitats (Blackstock et al, 1999; Petit et al, 2003; Ratcliffe, 1984), replacement of hay meadows with intensely managed pastures (Fitzpatrick et al, 2007; Green & Stowe, 1993), simplification of crop rotations (Harris & Ratnieks, 2021; Ollerton et al, 2014), and increased use of fertilisers and herbicides (Ollerton et al, 2014). Increasing urbanisation is also considered a major threat to insect biodiversity (Sánchez‐Bayo & Wyckhuys, 2019; Fenoglio et al, 2021; but see Goulson et al, 2002; Hall et al, 2017; Samuelson et al, 2018; Tew et al, 2021).…”

Effect of agroecological measures on honey bee colony development and survival in the Swiss context

“…Delayed mowing also provides an additional nutritional resource, with the blooming of clover, which provides honey bees with an abundant source of nectar and pollen in summer. Increased use of clover in grasslands is a low-cost way to improve the food supply for pollinators while supporting agricultural productivity, creating a win-win scenario (Harris and Ratnieks, 2021). All these results show the potential of implementing these floral measures in meadows to benefit honey bees.…”