Conventional and organic cropping systems at Suitia VII: Earthworms

Abstract

The earthworm communities were studied in an experiment with eight cropping systems (four conventional and four organic), carried out on silty clay soil. Earthworms were sampled during the three last years of the seven year experiment. Samples were taken with formalin in the autumns of 1986 and 1987 (one replicate of the experiment) and in that of 1988 with formalin and by taking soil-cores (all three replicates). Aporreclodea caliginosa (Sav.) was dominant in all cropping systems. The rest of the identified individuals were Lumbricus rubellus (Hoff.) and L. lerrestris (L.). A few L. castaneus (Sav.) were also found. There were no clear differences in the species composition between the conventional and organic cropping systems. Application of slurry caused a drop in the proportion of Lumbricus. Low total numbers were observed in 1987, possibly due to high winter mortality. In 1988, the average number (and SE) of earthworms was 23 (11.2) - 92 (49.8) ind. m-2 and their total dry weight 1.0 (0.54) - 3.2 (1.53) g m-2. The average number of cocoons in 1988 ranged from 5 (2.5) to 52.5 (26.3) coc. m-2. The highest abundances of earthworms and cocoons were observed in the organically cultivated vetch ley. The differences between the treatments in worm abundance were not statistically discernible. The mean size (mg dwt) of juvenile and adult A. caliginosa was similar in different cropping systems. The abundance patterns of earthworms differed in the replicates. This was related to the confounding effects of local water-logging and soil compaction in the field. Consistent differences in the soil conditions of the cropping systems resulting from the activity of earthworms are unlikely.