Keywords: Soil protection, Soil degradation, Soil fertility, Soil contamination, Good agricultural practice.
Protecting the many functions of soil is accepted as a fundamental responsibility by Governments throughout the World. Policy measures to achieve this aim vary widely as has their success rate to date. In the United Kingdom legal protection is provided largely through the planning process with a reliance on voluntary Codes of Practice and economic incentives to improve day to day management practices. The structure and content of this review is based on the Code of Good Agricultural Practice for the Protection of Soil published by the Ministry of Agriculture Fisheries and Food in 1993.
Maintaining or improving the fertility of agricultural soils is generally the aim of good practice. However in certain circumstances environmental demands on farmers may require a return to more natural habitats which require lower levels of fertility. There is strong pressure areas currently devoted to natural or semi-natural habitats, and legal protection is often afforded to them. The rational use of fertilisers and manures, lime, cultivations and rotations are all necessary to ensure that soils are maintained in good heart and can sustain production. The significance of declining soil organic matter levels under arable agriculture is uncertain.
Physical degradation by soil compaction is generally considered less of a problem in the United Kingdom than was the case 25 years ago. Continuing vigilance is needed, particularly where surface compaction, specifically in wheelings, are responsible for initiating much of the water erosion which occurs. A recent study suggests that 11% of soils in England and Wales are at a significant risk of erosion in at least some years when cropped to winter cereals. For these areas and particularly the 2% of land where there is a high risk, the management practices out-lined in the Soil Code need to be adopted by farmers. Further thought needs to be given to alternative land uses such as farm woodlands and biomass production, on soil conditions.
Atmospheric deposition remains the largest single source of soil contamination, albeit that it occurs at a relatively low rate over the whole of the country. Sewage sludge applications to land have been limited by specific legislation for several years and in the future other wastes will be adequately by recent regulations. Like sewage sludge the contamination of inorganic fertilisers by metals has been reduced in recent years. The application of animal manures, particularly pig and poultry manures, results in a gradual accumulation of metals in soil. Farmers should follow good practice to limit the rate of this accumulation and to monitor increases by soil analysis. Although clean-up technologies are being developed to rehabilitate contaminated soils the cost will seldom justify subsequent agricultural uses.
R J Unwin, ADAS, Bristol, UK.
24 pages, 2 tables, 36 refs.