Methods to diversify field margin plant communities. BD1607
Sponsor: DEFRA Countryside Management Division.
Collaborators: Farmed Environment Co., University of Sheffield

Overall objective:

To identify practical methods of increasing the botanical diversity of field margin strips and arable crop edges

1. To develop methods of establishing common dicotyledonous flowers in existing grass margins
2. To investigate the establishment and effects of hemiparasitic plants, notably Rhinanthus minor (Yellow rattle), on grasses in order to identify practical management methods to diversify margins
3. To test methods and impacts of soil fertility limitation treatments on the diversity of grass margins
4. To test methods of selectively reducing the biomass of dominant species in margins and arable crop edges
5. To develop seed introductions and selective management treatments in arable crop edges to re-create traditional weed communities
6. To draft a guidance note on the results for use by Project Officers

Executive Summary

GUIDANCE NOTES FROM DEFRA PROJECT BD1607
Methods to diversify field margin plant communities

This research project, based at Long Ashton Research Station and the University of Sheffield and with assistance from the Farmed Environment Company, set out to examine practical methods of increasing the botanical diversity of field margins. The project report has been drawn together by Dr Jon Marshall, previously based at Long Ashton Research Station and who can be contacted at: Marshall Agroecology Ltd, 2 Nut Tree Cottages, Barton, Winscombe, Somerset, BS25 1DU. Tel: 01934 844844; Email: jon.marshall@agroecol.co.uk; Website: http://www.agroecol.co.uk

Under the Countryside Stewardship Scheme (CSS), many project farmers have installed 2m or 6m wide grass margins. The majority have sown simple grass mixes, which, while providing a buffer against adjacent farming operations and structure for some vertebrates and invertebrates, typically remain botanically uninteresting. Under CSS and in some other schemes, there are prescriptions that are designed to encourage the rare cornfield flowers, which, as a group, contain more threatened species than any other habitat type in the UK. Where such species persist, the prescriptions can be successful. However, the seed bank for many of these species has usually been depleted in intensive arable land. This project addressed grass margins and arable crop edges. In both situations, which are considered separately below, the two limiting factors to botanical diversification are high soil fertility (with consequent competitive pressures) and lack of propagules.

Diversifying sown grass margins
1. Establishing seed into existing grass
Establishing seed into pre-existing grass swards is not straightforward. On heavy clay soils, poor establishment can be expected using sward disturbance techniques and oversowing. On such sites, the tendency towards grass dominance, reflecting high nutrient conditions, indicates that diversification is unlikely to succeed without attention to reducing soil fertility. It is therefore important to consider at the outset of margin establishment, if flowers are required. If so, then flower seed should be included at the outset with the grass seed (see project BD0404). On lighter soils, sward disturbance enhances flower seed establishment in grass. Slot-seeding gave the best flower establishment of the techniques tested, but harrowing and oversowing gave reasonable results. On such soils, sown grass margins can be diversified.

The successful introduction of plug-plants into swards irrespective of other treatment demonstrated that such a technique could be used to establish founder populations in a sward. Following establishment, the presence of R. minor and sward scarification may then become more important for successful recruitment from seed from founder plants. However, it was apparent that not all species were suited to the experimental planting sites. This effect may initially be masked by the delayed response of these larger plants.

· On clay soils, include flower seed at the establishment phase for diverse grass margins
· Once established, grass margins on clay are unlikely to respond to diversification efforts.
· On lighter soils, sward disturbance with a harrow or other cultivator, is needed to be sure of flower seed establishment
· Slot-seeding (e.g. Rotaseeder) or precision drilling into short grass gives best results
· Reducing soil fertility should be an objective of management, if botanical diversity is to be maintained
· Plug-plants are expensive but can establish after planting into swards
· Select plant species that are appropriate for the soils

2. Using Rhinanthus minor (yellow rattle) to reduce sward biomass
Whilst sowing yellow rattle on bare seedbeds is successful, on the basis of the Long Ashton experiments, establishment of Rhinanthus minor in some established swards is difficult. No yellow rattle established on a heavy clay site. It was established successfully on an alluvial, particularly where slot-seeding or a precision drill was used to introduce seed into the soil. The population levels of only 3 m-2 achieved on an alluvial loam soil were not sufficient to produce marked diversity effects over a three-year period. Drilling should be in autumn, as laboratory studies demonstrated that seed germination was highest after a cold treatment at 0-4oC for two weeks.

In newly sown swards in the Sheffield area, yellow rattle reduced the vigour of potential sward dominants, particularly grass species. Although the impact of R. minor varied between sites, overall it was shown that the grass component was mostly affected and this resulted in an increased relative abundance of the flowers in the sward. It can be concluded that the success of the treatments strongly depended on the site being investigated. If R. minor, an annual plant that relies on germination each year, is to be used as a tool for promoting forb abundance, then treatments must also favour its expansion and persistence.

· Yellow rattle can enhance flowers in mixed swards by checking grass productivity
· Yellow rattle is easily established as part of a seed mixture
· It is harder to establish in pre-existing margins, and did not establish on clay soil
· On lighter soils, yellow rattle can be introduced into existing margins with a slot-seeder or precision drill
· Sowing should be in autumn, so that seed can have a suitable cold treatment to promote germination
· Consider including yellow rattle as part of grass and flower seed mixtures for establishing margin strips

3. Sward management after seed or plug-plant introductions
Ultimately, the long-term success of any species introductions will depend on the application of a suitable management regime that maintains low levels of competitive exclusion and provides gaps in the sward for subsequent establishment and expansion. A treatment of the herbicide fluazifop-P-butyl was shown to strongly influence the dynamics of the sward through suppression of the grass component. However, as found with R. minor, the impact of fluazifop-P-butyl varied between sites and this was suggested to be due to differences in the range of grasses present. Although an application of fluazifop-P-butyl tended to promote the relative abundance of the flowers, a single treatment was associated with a decrease in the overall number of species present.

The treatment of scarification was applied to remove dead and living vegetation in an effort to promote the establishment of the sown species. However, the effectiveness of this treatment varied depending on the composition of the sward. It is suggested that the timing and intensity of scarification may also be important in determining the success of this treatment. The response to the spring cut in terms of values of above-ground biomass also varied between sites and this was mainly dependent on whether species were present that could respond positively to the initially lower levels of competition. A spring cut was shown to have a negligible effect on the number of sown species that were present but tended to regulate the number of R. minor individuals.

4. Reducing nutrient availability in grass margins
The lime, sulphur and sawdust soil ameliorants and a compaction treatment did not result in significant reductions in biomass productivity at the Long Ashton and Yorkshire sites. There was little evidence that these treatments encouraged diversity enhancement, opportunity for which was provided in the form of added seed, coupled with disking. However, as there were also no significant effects on soil pH, the question remains whether continual annual applications (only applied twice here) might in time result in modifications to productivity and sward composition. In the light of the Park Grass experiences, sward changes may take in the order of five to ten years to appear. The experiment at Radcot demonstrated that: a) fertiliser contamination has a major adverse impact on productivity and plant diversity, b) cutting and removal of vegetation on margin strips can result in reduced productivity over a period of five years (plant diversity is maintained) and c) soil-stripping to subsoil maintains low sward productivity (but this is an expensive and impractical option for creating diverse margins). To enhance or maintain plant species diversity in field margins, the key procedures that farmers should be encouraged to carry out are protection from fertiliser contamination by encouraging accurate field application, and annual removal of biomass.

· Fertiliser contamination of grass margins will enhance productivity and will reduce botanical diversity
· Encourage accurate fertiliser application in adjacent fields, to protect margins
· There is potential for amending soil pH using sulphur or lime, but further longer-term research is needed
· Cutting and removal of clippings can reduce productivity over time on some soils
· This technique is the most practical approach to limiting fertility and the encouragement of plant diversity in margins

5. Selective herbicides for reducing dominant components of swards
Herbicide development has promoted broad-spectrum products, rather than compounds with narrow specificity (Marshall, 2001). Therefore, most herbicides that are available for the manipulation of mixed plant communities found on field margins are likely to affect at least some of the desirable component species. Nevertheless, the field experiments demonstrate that there are opportunities to use reduced rates of commercially-available products to limit the growth of some common and less-desirable species in margins, such as blackgrass, couch grass, thistles, docks and Japanese knotweed.

Diversifying arable crop edges
6. Sowing rare arable weeds
Simple seed introductions of rarer cornfield flowers, such as corn marigold, can successfully establish new populations in arable field edges. Certain species were able to persist for over four seasons where herbicide regimes remained relaxed at the field edge, as with conservation headlands. Initial establishment is the key stage. Where the crop is not sown, or at least severely reduced in growth, the sown flower establishment is best. Avoidance of fertiliser is recommended (Kleijn & Van der Vort, 1997). Timing of sowing needs to suit the target species, though good data on rare weed germination periodicity is lacking. Here, species were selected with reportedly both autumn and spring germination patterns, though not all behaved as expected. Many of the species mentioned in Biodiversity Action Plans are reported as spring-germinating, but not all.

· Sowing seed of rare cornfield weeds can give rise to new populations
· Sow seed without the crop and without fertiliser additions
· Maintain the crop edge as a conservation headland, or as an uncropped wildlife strip
· Select sowing times to suit the chosen species (autumn or spring germinating)

Relevant pubications

Westbury, D.B. & Dunnett, N.P. (2000) The effect of the presence of Rhinanthus minor on the composition and productivity of created swards on ex-arable land. Aspects of Applied Biology 58, Vegetation Management in Changing Landscapes (ed Boatman, N.D., Clay, D.V., Goodman, A., Marrs, R.H., Marshall, E.J.P., Newman, J.R., Putwain, P.D. & Pywell, R.F. ), pp. 271-278. AAB, Wellesbourne.

Marshall, E.J.P. & Nowakowski, M. (2000) Herbicides for the overspray treatment of weeds in sown grass and wild flower margins. Aspects of Applied Biology 58, Vegetation management in changing landscapes, pp. 381-388. AAB.

Moonen, A.C. & Marshall, E.J.P. (2001) The influence of sown margin strips, management and boundary structure on herbaceous field margin vegetation in two neighbouring farms in southern England. Agriculture, Ecosystems & Environment, 86, 187-202.

Westbury, D.M., 2001. Shifting the competitive balance: The use of Rhinanthus minor and other techniques to promote forb abundance on productive sites. Ph.D., University of Sheffield, Sheffield, 465pp.