Effects of pig and cow slurry on the growth of Sitka spruce on oligotrophic peat and gley soils in Northern Ireland.

Abstract

Nutrients are normally applied to forest crops in the form of organic or inorganic fertilisers. Urea, rock phosphate and potassium chloride are the most' commonly used forms of N, P and K respectively in Northern Ireland. There are no important naturally occurring sources of P or K in the province which are suitable for use as fertilisers. Nevertheless agriculture in the province shows a surplus of nutrients (McAllister, 1971) due to the large quantities imported in fertilisers and in feedingstufTs for cattle, pigs and poultry. The input surplus has been estimated at 20 kg P and 25 kg K/ha on agricultural land per year. On the more intensive livestock farms much higher local . surpluses of nutrients exist and disposal of the excreta on grassland (which accounts for 90% of all agricultural land) can cause major problems. For example, grazed swards may be damaged or killed by severe scorching as a result of excessive applications of urine with subsequent recolonisation by inferior grasses; excessive dressings of excreta as slurry may produce a slow drying organic layer on the soil surface which renders it more liable to poaching, while the finer solids can block soil pores and restrict aeration; the high levels of potassium which may be built up in the soil increase the risk of hypomagnesaemia; and the spreading of slurry on land under unsuitable conditions increases the risk of pollution and nutrient enrichment of drainage water. These problems have been described and discussed by many workers e.g. McHugh (1973), Kelso (1973), Gracey (1974) and Watters and Thompson (1974)...