9938: The effect of organic farming systems on aspects of the environment - desk study OF0123

Unwin, Roger; Bell, Barbara; Shepherd, Mark; Webb, John; Keatinge, Ray and Bailey, Steven (1995) The effect of organic farming systems on aspects of the environment - desk study OF0123. Report no. OF0123, ADAS.

Summary

Key Conclusions
1. The crop rotations of organic systems maintain landscape diversity and biodiversity whilst the maintenance of field boundaries on organic units produces benefits to a wide range of organisms.
2. Inorganic nitrogen fertilisation and herbicide treatments of conventionally managed grassland has reduced the floral diversity of permanent pastures and maintained the low diversity of re-seeded pastures, greatly reducing their value as wildlife habitats.
3. Pesticide use is responsible for the removal of food sourcesfor birds and mammals in the form of weeds and invertebrates, as well as removing whole populations of potentially beneficial insects.
4. The majority of water pollution incidents from farms are caused during storage and spreading of cattle and pig slurries. A higher proportion of organic cattle and virtually all organic pigs are kept on solid manure systems and therefore are les of a risk.
5. The nitrogen balance of individual 'conventional' and 'organic' systems will depend greatly on the circumstances and management practices of the individual farms. Consequently it is not possible to generalise that one system is always better than the other in terms of nitrate leaching risk. With this qualification the literature does indicate that generally, organic systems offer less risk of nitrate leaching.
6. Organic systems are less likely to cause loss of phosphate into surface and ground waters. Both leaching and loss in eroded soil are likely to be reduced.
7. Organic management practicess such as rotations, the regular use of manures and non-use of pesticides usually increase soil organic matter contents.
8. Organic practices are likely to increase earthworm numbers compared to conventional systems. The increased numbers are universally acknowledged to benefit soil fertility although such effects are difficult to quantify.
9. Soil erosion is less of a problem on organic units.
10. Accumulations of copper and zinc in soils are much reduced in organic systems because organic pig and poultry producers do not supplement feeds with these metals as growth promoters. Copper fungicides are more widely used on organic farms and their use should be carefully monitored to prevent harmful effects.
11. The practices adopted by organic farmers can reduce emissions of nitrous oxide and methane. Ammonia emissions will not necessarily be less in organic than in conventional farming.
12. Organic farmers adopt practices which benefit the landscape. They maintain and introduce features largely because they are required by the Organic Standards to do so. They introduce such management practices because they are technically necessary for successful organic production.

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