Field tests on the side effects of pesticides on earthworms: Influence of plot size and cultivation practices

Standardized field tests, which ran for up to one year, were used to investigate the side effects of pesticides on earthworms under agricultural conditions. The studies were run on 10 × 10 m replicate plots of flat, uniform grassland areas. Benomyl was used as a reference substance. To exclude migration of earthworms from untreated plots to plots where earthworm abundance had been reduced by the test compound, a mechanical barrier was used. The results showed, that an invasion of earthworms from surrounding grassland into benomyl-treated plots without barriers did not occur during a one-year study. In a further study, parathion-methyl was used to investigate the combined effects of cultivation practices and pesticide treatments on earthworms, since laboratory data could not exclude a possible hazard for earthworms under practical conditions. For this study, the pesticide was sprayed on different plots on which either (1) the grass cover was mulched, (2) the grass was cut and removed, or (3) the grass was ploughed and re-seeded just before application on the bare soil. Earthworm samples were collected about two, five and 11 months after application for species identification and enumeration. Earthworms did not seem to be influenced differently by mulching or by cutting and removing the grass. Ploughing, however, reduced earthworm abundance significantly. The results indicated that 0.3 and 1.5 kg a.i. ha−1 of methyl-parathion had no effects on the earthworm abundance. This indicated that earthworm field studies performed on grassland yield the same results as those which are performed in agricultural soils.