Soil microarthropod assemblages under different arable crop rotations in Alberta, Canada

Abstract

We examined the effect of increasing crop diversity on the soil microarthropod assemblage within organic and low-input cropping systems in Alberta, Canada. Microarthropod assemblages were contrasted in rotations of either one or three crop species (low-input system) or two or four crop species (organic system), over 2 years. Mites were sorted to family level and oribatid mites to species level. The abundance of microarthropods and the species richness of oribatid mites in the second year were extremely low in comparison with the first year in both cropping systems. In the organic system, there was a greater number of individuals and mite taxonomic richness per core in the four-species rotation than in the two-species rotation in the first year. There were no differences in the microarthropod assemblages between the two organic rotations in the second year. In the low-input system, the dominance of mite families differed between the one- and three-species rotations in the first year. Species richness was strikingly different between the two cropping systems in the first year, with 23 oribatid species found in the organic rotations compared with only 12 found in the low-input rotations. Far fewer species were recovered in the second year and differences in species richness between cropping systems were not as marked. Whilst our study shows that cropping systems can affect microarthropod assemblages, the results suggest that year to year variation in mite assemblage structure is extremely large relative to the effects imposed by cropping systems. The richness of oribatid species (27 in total in this study) is amongst the highest recorded in arable agricultural soils anywhere in the world. The oribatid assemblages were dominated by Brachychthoniidae species which appeared to be able to tolerate arable agricultural practices such as tillage. The dominance of this group may be unique to Canadian prairie soils.