ABSTRACT
Organic wastes and agriculture The application of organic wastes, notably livestock manures, to land has historically been important for maintaining soil fertility in terms of both nutrient status and organic matter levels. However, with the increased specialisation and intensification of livestock farming (Chapter 1) a number of important trends have emerged. Firstly, livestock manures and slurries are produced in considerable quantities and, unlike most domestic sewage, are usually disposed of without treatment. It is estimated that the annual livestock waste production on UK farms totals some 191 million tonnes per year (Smith and Chambers, 1995). Of this approximately 80 million tonnes is slurry or manure requiring handling, storage and spreading, whilst the majority is voided directly to the land by grazing animals (Smith et al., 2000). An estimated 95% of all cattle manure is returned to land in the UK, with rates of application between 30 and 300 t ha - 1 (Johnes et al., 1996; Jackson and Smith, 1997). Secondly, intensification within the livestock industry leads to large numbers of animals being concentrated in relatively small areas and consequently the production of large volumes of waste at a single site. For example, a dairy cow typically produces 50-60 litres of excreta per day, and uses upto 3 kg of straw for bedding (loose housing) and up to 351 of water to wash the milking parlour and dairy equipment. A typical dairy farm might have 100 milking cows. Over a six-month winter period alone these would generate over 1,000,0001 of urine and faeces, plus 55 tonnes of soiled straw bedding and 640,0001 of dirty water; all of which has to be disposed of safely. Similar calculations can be made for other types of livestock (Table 5.1). Thirdly, The predominance of livestock farming in the west of the UK and arable farms in the east, means that the traditional use of farm wastes on arable land is increasingly restricted.
