Sown Margins Research Articles

Selected flowering plants as a habitat for pollinators and natural enemies in field margins of a watermelon crop—implications for crop yield

The practice of field margins management using mixtures of selected plants to provide habitats for pollinators and natural enemies of pests, and possible impact on crop yield, was studied for two mixtures (mixture A: Borago officinalis, Coriandrum sativum, Glebionis coronaria; mixture B: Vicia sativa, Sinapis alba, Phacelia tanacetifolia) in watermelon, cv. Karistan. The sown margins attracted primarily Apis mellifera and Halictidae bees (Lasioglossum spp.), and a few other Apidae (Anthophora sp., Eucera sp., Bombus sp.) over a flowering period of 6 weeks (beginning of April to mid-May). Pollinators on watermelon flowers were mainly Halictidae (Lasioglossum spp.) and fewer honey bees, from mid-May to mid-June. Shannon’s (Η) diversity index of parasitoids was higher in mixture B while their abundance did not differ between the plant mixtures, although it varied during the season. Higher weight/fruit, lower proportion of undeveloped/mature seeds per fruit, and higher Brix level in the field with the sown margins compared to a commercial watermelon, cv. Karistan, field, under common agronomic practices, suggest a positive effect of the sown margins on the crop yield.

The value of two agri-environment scheme habitats for pollinators: Annually cultivated margins for arable plants and floristically enhanced grass margins

We investigate the potential benefits to pollinators of two agri-environment scheme habitats, annually cultivated and floristically enhanced grass margins. The former encourages annual plant species whereas the latter targets the provision of perennial plants, both may benefit foraging pollinators, many of which have declined in the UK since the 1980s. We surveyed thirty cultivated margins and thirty floristically enhanced grass margins across the UK for pollinators, which included bumblebees Bombus spp., solitary bees and hoverflies Syrphidae. Pollinator abundance was then related to margin attributes such as age, width, soil fertility and adjacent habitat type. For cultivated margins we also investigated relationships with cultivation and rotation, and for floristically enhanced margins time cut. Plant preferences of foraging pollinators were recorded in 2019. On cultivated margins, target annual plants were frequently recorded on plots and were repeatedly visited by pollinators with management significantly influencing visitation rates. For example, plots which had been created with ploughing attracted fewer solitary bees and bees overall than those created with minimum tillage. Annually rotated cultivated margins were associated with lower flower abundance, broad leaved species cover and vegetation heights which resulted in lower total bee abundance. We therefore advise that cultivated margins be left in situ on farmland over longer periods. Older floristically enhanced grass margins became dominated by grass and contained fewer flowerheads to support foraging pollinators. Compared to those established via natural regeneration, sown margins were associated with increased bee and Syrphidae abundance, which is probably linked to the high flowerhead abundance and coverage of broad-leaved species on sown plots. Our pollinator foraging data from 2019 showed that tolerance of some agricultural weeds should be advocated. Our results highlight the complementary benefits of these agri-environment scheme habitats to pollinators. We suggest that where arable pollinator conservation is a priority both habitats be provided.

Vegetation development of sown grass margins in arable fields under a countrywide agri-environment scheme

Farmers were paid to establish 6 m wide sown grass strips in arable field margins under the Countryside Stewardship Scheme in England, UK. One hundred and sixteen sites in eight regions were surveyed to determine if grass margins had been established successfully and the extent to which they were colonised by forbs. Sown margins had more grass and fewer weed species than naturally regenerated sites. Grass margins contrasted with normally cropped sites, having greater species richness of grasses, forbs and perennials and more bird, butterfly larva and bumblebee foodplants. Mesotrophic grassland forbs were scarce in margins established from basic grass seed mixtures but significantly more abundant if included in the seed mixture. Annuals were more prevalent in sites up to 2 years old but species composition was not related to age in sites over 2 years old. Variation partitioning showed that overall species composition was related to seed mixture type, region and soil properties but there was little overlap in the variation explained by these environmental variable sets. Habitat context and management practices did not explain any variation in species composition. Perennial grassy vegetation was established successfully using basic grass seed mixes but only competitive species colonised subsequently. Diverse seed mixtures containing mesotrophic grassland forbs merit support in agri-environment schemes because they do enhance the botanical diversity of sown grass margins.

The effect of arable field margin composition on invertebrate biodiversity

A replicated field experiment designed to compare five types of field margin in terms of their invertebrate biodiversity was established in North Yorkshire, UK. Four replicate margins on arable land each contained five treatment plots 72 m long by 6 m wide. The treatments were: (1) cropped to the edge; (2) sown ‘tussocky’ grass mix; (3) sown ‘grass and wildflower’ mix; (4) Split margin (3 m ‘tussocky’ grass adjacent to hedge and 3 m ‘grass and wildflower’ next to crop); and (5) natural regeneration. Invertebrates were sampled by pitfall trapping, sweep netting, and butterfly and bumblebee transects, and identified to species level. The use of different flower species by foraging bumblebees was also examined. Despite all treatments containing a flush of annual weeds early in the establishment year, the five margin types were distinct in their vegetation composition by their first mid-summer. Where statistically significant results were obtained for invertebrates, avoidance of the ‘cropped’ treatment was by far the commonest observed response. This tendency could be clearly demonstrated amongst the carabids, spiders, butterflies, bumblebees, millipedes and harvestmen, with margins often containing double or more the number of invertebrates of similar areas cropped to the edge. Having avoided the crop, preferences for other margin types were mixed, but there was a marked tendency by many nectar and/or pollen-feeding, flying insects towards greater abundance on those margins containing sown ‘wildflowers’ (e.g. butterflies Meadow Brown and Ringlet, Bumblebees, Pollen Beetle Meligethes sp.) or flowers either sown or unsown (Soldier Beetle Rhagonycha fulva). There was a less strong tendency for predatory species occurring in the vegetation canopy and depending on small, especially flying insects for food, to also prefer the flowery treatments (e.g. total spiders caught by sweeping, seven-spot ladybird). Harvestmen in autumn reject natural regeneration in favour of any sown treatment. Only one species, the carabid Nebria brevicollis, was trapped in higher numbers in the cropped treatment than on any sown margin, and then only in autumn. Of the six common bumblebee species, the two longest-tongued species showed different patterns of flower visitation from the remaining four. These results clearly demonstrate that sown field margins can rapidly produce substantial biodiversity benefits on arable land, with the resulting fauna influenced by the type of field margin created.