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One of the challenges of research in soil ecology is to assess the impact of tillage managements on soil invertebrates. It is known that tillage practices change soil water content, temperature, the degree of mixing of crop residues within the soil matrix and the physico-chemical environment for soil organisms. The present study tested whether no-tillage (NT) or a conventional tillage (CT) of a cereal (durum wheat; Triticum durum) field in a semi-arid zone of northwestern Tunisia could improve the biological activity and diversity of soil invertebrates, especially arthropod and earthworm communities.

The experiment was conducted in January 2000 at two different sites (Mahasse/Kef Governorate and Krib/Siliana Governorate). Soils (Brunisols, isohumic or fersialitic soil) were silt/clay in Mahessen and sand/clay in Krib. After three and four years, soil fauna was sampled with two methods (quadrat and pitfall trap) over 7 months for the last two growing seasons (200212003 and 200312004). We hypothesized that: (i) soil fauna richness, abundance and diversity would be lower in CT soils than in NT soils and (ii) the move from CT to NT may improve the soil biological component under semi arid conditions.

380 invertebrates (37 species) and 309 invertebrates (24 species) were collected by quadrat and pitfall trap methods, respectively. NT greatly enhanced the species richness (from 26 species in CT to 34 species in NT) and abundance (from 61 individuals in CT to 319 individuals in NT) of soil invertebrates with quadrat method. Only abundance was significantly enhanced with pitfall trap method (from 78 individuals in CT to 235 individuals in NT). So, abundance, species richness and diversity of soil arthropods were significantly higher(P < 0.05)with NT than with CT. Soil fauna patterns showed that management mode affected also the abundance of earthworm community. These findings confirm our first hypothesis.

Predators (mostly Carabidae), detritivore (especially: Formicidae, Dolicoderidae, Lumbricidae) and herbivore (represented here by Julidae, Pyrrhochridae and some Scarabaeidae) were significantly (P < 0.05) more abundant with NT than with CT. The biological index V (index which compares the relative increase or decrease of the population density between the two tillage modes) showed that all major taxonomic groups were extremely inhibited by CT, confirming our second hypothesis.

So, NT seems to be beneficial to biological soil component where it favoured the establishment of diverse soil communities than did CT in durum wheat cropped field. Furthermore, soil fauna may enhance crop-residues decay processes. (C) 2010 Elsevier B.V. All rights reserved.