The use of nitrogen fertilizer on alternative grassland feeding refuges for pink-footed geese in spring.
Abstract
Intensive agriculture often reduces biodiversity on farmed land, but the converse situation, of wildlife damaging agriculture, is also important. A striking example is agricultural damage by increasing populations of wild geese (Anser brachyrhynchus). Alternative feeding refuges, designed to reduce damage, will be most effective if the grass swards are made as attractive to geese as possible. This paper describes an explicitly experimental study in northeast Scotland during 1990-93, which investigated the effectiveness of different rates of application of nitrogenous fertilizer on the amount of grazing by pink-footed geese in spring, compared split-application with single-application of spring fertilizer, and evaluated the use of slow release fertilizer in winter. The amount of goose grazing, measured from cumulative dropping density, increased with application rates of spring fertilizer, up to around 80 kg N ha-1, in parallel with a similar increase in grass production. Beyond this level there was little further increase, and cost-effectiveness, measured as the percentage increase in dropping density per kg N ha-1 applied, was greatly reduced. Dropping density and grass production did not differ significantly between split-application and single-application of spring fertilizer. Split-application should reduce the risk of nitrogen leaching in cold wet seasons, but the cost of application would be double that of single-application. Overall, cumulative dropping density and grass production in late May were not significantly greater in plots treated over the winter with slow release fertilizer than in untreated plots. Dropping density was higher in treated plots than in untreated ones during a short mild period in early spring. Slow release fertilizer may be of benefit in mild winters, but is more expensive than conventional nitrogenous fertilizer. This study has shown that nitrogenous fertilizer can greatly increase goose grazing on sacrificial grassland refuges in spring and is a useful tool in reducing conflict between farmers and increasing goose populations.