Spatial and Competitive Aspects of Arable Field Margin Flora.

Abstract

Distribution patterns of plants with different life history groups from field boundary to mid-field were monitored over three years. Longer-lived species were generally confined to the boundary at the cropped site; whereas at the set-aside site perennial grasses ingressed from the boundary, biennial dicots increased rapidly in the field and annual dicots declined. The soil seed bank declined at the former site, but increased over time at the latter.
The majority of Bromus sterilis (100%), Chaerophyllum temulentum (97%) and Anthriscus sylvestris (90%) seeds disseminated <=lm of source, with maximum dispersal distances of <=3m. At high wind speed (0.8m/s) 84% of B. sterilis and 93% of Galium aparine disseminated <=1m from source (with the remainder dispersed up to 3.5 and 1.75m respectively) compared with 99% and 100% respectively, at low wind speeds (0.4m/s). Secondary dispersal by the combine, moved B. sterilis seeds <=7m behind and <=53m in front of the source, with 42% deposited within 1m of it.
A questionnaire survey of farmers indicated that farmers currently use more accurate fertilizer distributors (79%) than a decade ago (43%). Of those with broadcasters 77% took precautions to reduce fertilizer misplacement into the boundary.
Misapplication of fertilizer into the field boundary was effectively reduced by fitting a headland deflector to a twin disc distributor; oscillating spout machines spread fertilizer unevenly over the whole field. All machines showed localized nitrate over-dosing.
Nitrogen application increased the biomass of eight selected field margin species but growth was reduced by competition with wheat >Holcus lanatus >Poa trivialis >unvegetated plots. Perennials harvested in the second season showed no response to nitrogen fertilizer. A. sylvestris survived longer than G. aparine or B. sterilis when seeds were sown into established grass swards. Transplanted B. sterilis seedlings were more impoverished in grass than unvegetated plots. B. sterilis and G. aparine were more responsive to nitrogen application than other species.
In additive mixtures B. sterilis was more aggressive than H. lanatus >P. trivialis >Festuca rubra; all species competed similarly for resources. B. sterilis reproductive production was greater when nitrogen was applied, and when grown in monoculture.
Management plans to improve the floristic composition of field margins are discussed.