Fertilising

General considerations

1. Dune-building grasses are adapted to growing in nutrient-poor soils, so transplanted offsets usually survive quite well without the benefit of extra nutrients. But where a quick ‘take’ is essential, it may be worth fertilising transplanted grasses to increase their vigour and rate of tillering. Fertilising is much more important where an area has been seeded. It can also be useful to promote the growth of established vegetation in partly stabilised areas. On machair sites, fertilising does not always do much good and it may be that plant growth here is limited by a trace element deficiency in addition to, or instead of, a lack of major nutrients (Countryside Commission for Scotland, 1978, p10).
2. Where fertilisers are used on unstable soils, it helps to apply a sand binder or mulch to reduce soil movement and ensure that the fertiliser remains available to the plants. Note that some organic mulches are rich in nutrients and their use may make other fertilisers unnecessary.
3. Because leaching is rapid through porous soils, most dune fertilisation programmes use a slow-release formulation such as ‘Enmag’. However, some researchers have had equally good results from straight agricultural fertilisers (see below), which are cheaper. On dune grasslands or machair surfaces not subject to very rapid leaching, there seems to be little advantage in using slow-release fertilisers.
4. Fertilising dune soils increases the density and luxuriance of grasses at the expense of lower-growing herbs and bryophytes. This may not be desirable on nature reserves. Where possible, restrict fertiliser applications to the minimum necessary to maintain the typical flora for the site. For example, less fertiliser is needed to maintain an open marram-dominated community on mobile dunes than a mowable sward on backdune pastures (see the suggested rates below).

‘Enmag’

‘Enmag’ slow-release fertiliser, produced by Scottish Agricultural Industries PLC, Firth Road, Houstoun Industrial Estate, Livingston, West Lothian (tel: 0506 39281) has seen widespread use on open marram dunes. It contains 5% nitrogen, 24% phosphate, 10% potash and 10% magnesium in an inorganic, granular formulation which is slowly soluble but has variable particle sizes to give a prolonged, steady release. ‘Enmag’ costs £17.27 plus VAT per 25kg sack (1986 price), and is available from the above address and from distributors nationwide. Charlton (1970, p43) reports good results on marram grass, compared to unfertilised controls and straight agricultural fertilisers, but a slow effect on sea lyme grass. The manufacturers recommend a rate of 10-15g per plant applied around the base, or spread at 70g per square metre, which is 700kg per hectare. For newly planted or seeded areas, repeat this treatment three times in the first year (eg at the time of autumn sowing, in spring and in mid-summer).

Other fertilisers

Research by Paul Johnson and Professor A D Bradshaw of the University of Liverpool suggests that nitrogen is the crucial nutrient in short supply in marram dunes, and that application of a straight nitrogen fertiliser such as ammonium nitrate is sufficient to promote plant vigour and increase the rate of tillering by up to four times over unfertilised controls. Ammonium nitrate is relatively cheap (prices vary greatly depending on the amount purchased and the supplier, so shop around) and concentrated, and for most volunteer-type projects it can be carried in buckets and hand broadcast at the rate of 50kg per hectare (4416 per acre) per treatment with two treatments per year for the best results. This can be reduced to 25kg per hectare (2216 per acre) each time for economy but in either case the first application should be a week or two after planting to give the plants time to root.

For fertilising transplanted marram grass, the Countryside Commission for Scotland (CCS, 1985) recommend a top dressing in April, June and August of the first year, and again in April of the second year. Apply 30g per square metre of ‘Nitram’, ‘Nitrashell’ or ‘Nitro-top’ agricultural fertilisers. Alternatively, all-nitrogen fertilisers can be used at a rate of 10g per square metre. Leave newly-seeded areas until about a month after sowing, and then apply fertiliser in about mid-April, mid-June and mid-August. Supplement the first application with superphosphate. Expressed at g/sq m of N:P:K:, the initial dressing should be 4:10:10 and subsequent dressings 4:2:2. For further details see ‘Reseeding of Dune Pastures’ (CCS, 1980).

On machairs straight agricultural fertilisers are likely to be as effective as slow-release formulations (Countryside Commission for Scotland, 1977). Formulations used in various trials have differed so that it is not possible to give a standard rate or frequency of application (for details, see Adriani and Terwindt, 1974, pp34-44, Seaton, 1962 and Nash, 1962). Prices also vary according to formulation and amount purchased. The usual first-dose fertiliser is granulated superphosphate (NPK), applied at a rate of between 300kg per hectare (2651b per acre) and 450kg per hectare (40016 per acre) either all at once at the time of sowing or divided into two equal applications in spring and early summer. Spring-sown areas usually need a further application of nitrogen at 112-200kg per hectare (100-17016 per acre) in August or September.