The effects of four conventional and four organic cropping systems on the crop yield and yield quality, on the microbial activity of soil, on weeds, plant diseases, insect pests and earthworms were compared in a field experiment on the Suitia Experimental Farm in Southern Finland in 1982—1988. In the conventional cropping systems, industrial fertilisers and chemical pesticides were used according to practices adopted on actual farms in Southern Finland. In the organic cropping systems, plant nutrition was based on biological N fixation by legumes and organic manures. No chemical pesticides were used. The average yield of barley in organic cropping varied between one quarter and half of that in conventional cropping. The yields of winter wheat, oats and potato were about 40 % of those obtained conventionally. The yields of clover-grass leys in organic farming were similar to those of grass-leys in the conventional system. Unfortunately, the clover-grass leys outwintered after the first year. The primary reason for the poor crop growth in the organic cropping systems was apparently the acute N deficiency caused by poor performance of legumes, low N content of organic manures and N losses in anaerobic conditions often occurring during winter and early spring. Pronounced soil compaction and anaerobic conditions in organic cropping systems had a harmful effect on the microbiological activity of soil as well as on earthworms. Weeds, plant diseases and insects were not a remarkable problem in any of the cropping systems
