Effects of manure treatment and soil compaction on plant production of a dairy farm system converting to organic farming practice

Tn a dairy farm system during conversion from conventional to organic farming practice, the effects of different cattle manure treatment methods, fertilisation level and soil compaction were studied over a period of 6 years. Yields, botanical composition, earthworm quantity and soil porosity were monitored. The manure was treated as diluted, aerated and mechanically separated slurry (solid compost on tilled land and liquid fraction on ley). There were only small differences in total yield between the different methods of manure treatment. Increasing the manure rate from 90 to 130 to 180 kg N ha(-1) year(-1) increased the average dry matter yields of mixed pasture from 6.2 to 6.8 to 7.0 t ha(-1) year(-1) and decreased the percentage of legumes in ley and green fodder. Soil compaction by tractor traffic decreased the average dry matter yields in ley from 9.0 to 6.6 t ha(-1) year(-1). Compaction had a stronger influence on yield than either manure treatment method or nutrient level. Soil compaction reduced the actual air-filled pore space from 12 to 7% and reduced the number and mass of earthworms. It was concluded that to improve yields in this organic farming system it was more important to avoid soil compaction than to increase the manure rate or to choose one specific manure treatment method.