A comparison of the effects of minimum-till and conventional-till methods, with and without straw incorporation, on slugs, slug damage, earthworms and carabid beetles in autumn-sown cereals

SUMMARY The present study compared slug, earthworm and carabid beetle abundance and slug damage to plants in minimum tillage (MT) and conventional tillage (CT) autumn-sown cereals. Winter barley was sown by CT and MT for 3 years followed by winter wheat for 6 years on a light-textured soil (Trial 1). Each cultivation was split so that straw was incorporated into the soil during cultivation in one split while the other did not receive straw. A similar investigation with winter wheat, over the same period, was undertaken on a nearby heavy-textured soil (Trial 2). The effects of method of cultivation and soil incorporation of straw on slug abundance and damage, and on earthworm populations were measured. Additionally, at Trial 1, the effects of cultivation and straw treatments on carabid beetle occurrence were measured in years 5–9. Over the 9 years, the method of cultivation had a significant effect on slug numbers in each trial. Slugs were more numerous in MT than CT plots, significantly so in 3 of the 9 years in Trial 1 and in 5 years in Trial 2. In Trial 1, slug numbers were significantly greater on no-straw than straw plots in 3 years as well as for the 9 years combined. Slug numbers did not differ between straw and no-straw plots in Trial 2. Slug numbers varied significantly between years and were influenced by factors other than the method of cultivation and straw application. Slug damage to seed and seedlings was quite low in each year (1–2%). Slug damage to cereal leaves at GS 23 was widespread in both trials, and severe in some years. MT had more leaf damage than CT in 5 of the 9 years in each trial, significantly so in 3 years in Trial 1 and in 4 years in Trial 2. Straw did not affect leaf damage in either MT or CT. Slug damage was not related to, nor did it affect either ear density or grain yield. The dominant slug species was Deroceras reticulatum. Earthworm numbers were significantly greater in MT than CT, for combined years, in each trial. Annually, these differences were significant for 5 years in Trial 1 and 2 years in Trial 2. Straw plots had significantly more earthworms than no-straw, for combined years, in each trial. The latter differences were significant for 5 years in Trial 1 and 3 years in Trial 2. In MT, the positive effect of straw on earthworm numbers was significant in Trial 2 but not in Trial 1. In CT, the latter effect was significant in each trial. Lumbricus species were more numerous in MT than CT and in straw than no-straw treatments. The impact of cultivation on numbers of carabid beetles was species-specific. The large beetle, Pterostichus melanarius, was significantly more numerous in MT than CT in 2 of the 5 years and for the aggregate of 5 years. Small carabids (Bembidion species and Trechus quadristriatus) were significantly more abundant in CT than MT in 3 of the 5 years as well as for the aggregate of 5 years. Straw did not affect the number of any or all carabid species either for combined cultivations (MT + CT) or within either MT or CT. It is concluded that MT increases slug numbers, slug damage and earthworm numbers relative to CT cultivations. MT favours large carabid beetles and CT favours small beetles. Straw incorporation increases earthworm numbers but not slugs, slug damage or carabid beetles. Slug damage to cereal leaves does not affect ear density or grain yield in either MT or CT crops when sown to a depth of 40 mm and before 18 September.