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Individual study: Winter application of slow-release fertilizer on grassland feeding refuges for pink-footed geese Anser brachyrhynchus at Loch of Strathbeg RSPB Reserve, Aberdeenshire, Scotland

Published source details

Patterson I.J. & Fuchs R.M.E. (2001) The use of nitrogen fertilizer on alternative grassland feeding refuges for pink-footed geese in spring. Journal of Applied Ecology, 38, 637-646

Summary

In the UK. increasing populations of wintering geese Anser spp. may cause agricultural damage by grazing on pasture land and winter-sown crops. In some areas alternative feeding refuges have been established which, if made as attractive as possible to the geese, are more effective at reducing damage to nearby fields.

An experimental study was undertaken on a nature reserve in north-east Scotland to investigate the effect of application of slow-release fertilizers to a grassland feeding refuge upon the amount of pink-footed goose Anser brachyrhynchus grazing.

Study site: The study was undertaken during 1990-92 at the Loch of Strathbeg Royal Society for the Protection of Birds reserve in north-east Scotland. Within the reserve are eighteen or so grass fields at its northern end which were used as a night roost by around 30,000 pink-footed geese Anser brachyrhynchus in the spring. These fields were all dominated by perennial rye-grass Lolium perenne and grazed by sheep and cattle in summer, when they also had regular applications of inorganic fertilizer.

Three grass fields that had regularly been used by geese throughout the winter of 1992-1993 were selected for the experiments. No livestock were grazed on the fields from September until the beginning of May.

Slow-release fertilizers: Slow-release fertilizers generally fall into one of two categories:

i) urea-based resins – e.g. isobutylidene diurea (IBDU), or
ii) water-soluable chemicals with water resistant coatings that break down gradually giving a slow fertilizer release over time

The two materials used in this study were:

i) IBDU (BASF Floranid: Kings Horticulture, Colchester, UK), a fertilizer recommended for early winter application to amenity turf
ii) a coated water-soluble nitrogen (N) fertilizer (Lawnbuilders: Scotts UK Ltd., Godalming, UK).

Slow-release fertilizer application: The two fertilizers, formulated as small free-running granules, were spread using a horticultural hand-pushed spinning-disc applicator designed for the application of slow-release fertilizer to amenity turf. The applicator was calibrated for each of the two fertilizer types to deliver a nutrient rate of equivalent to 50 kg N/ha.

Nine separate blocks were established in these fields avoiding features such as standing water, patches of rushes e.g. soft rush Juncus effusus, and ditches. Each of the blocks was divided into three adjoining 25 x 25 m experimental plots. The two different fertilizer treatments were randomly assigned to the two outer most plots in a block. The third (middle plot) was left untreated as a control, thus ensuring that geese entered a fertilized area from unfertilized grass and not directly from another treatment. The fertilizers were applied to the three fields on 22 December 1992.

Goose dropping densities: Goose dropping density was used to estimate the amount of goose grazing on the experimental strips. Nine permanent 5 m² quadrats each marked with a single peg (such marker pegs have previously been shown to have no effect on dropping density) were established in each block. Dropping counts were made immediately prior to the experiment to test for variation between areas selected for the treatments, and subsequently at about 2-week intervals from time of fertilizer application to the end of the dropping count census. Each quadrat or sample area was a circle with 1.26 m radius delimited by a length of cord stretched between two canes. Within this area all droppings were counted and removed (thus these would not be counted again during subsequent visits). When two or more droppings were encountered together (often in piles of five or more) these were recorded as a single dropping as they were likely to have originated from a single roosting bird. Cumulative dropping totals were calculated.

Grass production: Grass production over the duration of the study was measured by erecting a series of exclosures made from sections of rabbit-proof wire mesh 0.5 m high and 4 m long. This was folded to produce a 1 x 1 m square exclosure, topped with a mesh lid. The exclosures were pegged to the ground with one wire peg at the base of each side. Two exclosures were erected in each experimental plot immediately after fertilizer application and left until the grass was harvested. The grass was mown using a hedge trimmer with a 350 mm wide reciprocating knife blade. At the end of April, each exclosure was removed and the first peripheral 10 cm of grass was cut and removed to avoid any edge effect. The trimmer was then rested on the ground and pushed through the grass to achieve a cut of about 2 cm high, similar to the sward height in the goose grazed areas. The grass samples were dried in a drying oven at 80ºC for 16 hours. The weight of each was then measured and the dry matter (DM) i.e. grass production, under each exclosure, calculated as grammes DM/m².

Stock were excluded from the field during the course of the experiment and the only other large grazing animals present were rabbits Oryctolagus cuniculus.

Dropping density: There were no significant differences in the cumulative goose-dropping densities between treatments, whether in the middle of March or at the end of April (see Table 1, attached). There was considerable variation in the deposition rates over the study period (winter-spring 1992-1993), but only on one occasion, the 4 March 1993 count, was there a significantly higher count compared with the controls.

Grass production: Again, there were no significant differences in dry matter grass production between the two fertilizer treatments (see Table 1, attached). There was also no correlation between mean dropping density and grass production in the same plots.

Conclusions: There appeared to be little overall benefit of winter application of the two slow-release fertilizers tested as there was no significant variation between treatments in either dropping density or grass production. A brief increase in dropping density in treated plots recorded in the early spring may have occurred as a result of increased grass growth stimulated by nitrogen release following an exceptionally warm period of weather in early February. This hinted that slow-release fertilizers might increase goose-grazing only in mild winters or during mild periods during an average winter. However, the high cost of such fertilizers would probably be a constraint on their widespread use, even if further research genuinely showed them to be effective. Other fertilizers and application times would appear to be more effective at increasing the amount of pink-footed geese grazing (see Cases 101 and 102).


Note: If using or referring to this published study, please read and quote the original paper. This can be viewed at: http://www.blackwell-synergy.com/doi/abs/10.1046/j.1365-2664.2001.00627.x