Soil microarthropod community structure and dynamics in organic and conventionally managed apple orchards in Western Colorado, USA

We studied the influences of organic and conventional management practices on microarthropod diversity, densities, and dynamics in apple orchards on t he Western Slope of Colorado. The 'organic' orchards differed from the 'con ventional' orchards in that they used natural fertilizers (versus synthetic ) and did not use insecticides and/or herbicides. Based on findings from an nual agroecosystems, we hypothesized that the conventionally managed (CM) a pple orchards would support a lower diversity and density of soil microarth ropods than the organically managed (OM) apple orchards. We located nine si tes, three OM orchards, three CM orchards, and three native sites. From eac h site, microarthropods were extracted from soil samples taken from June to September of 1997 and April to September of 1998. The richness and diversi ty of functional groups and families did not differ among the OM orchards, CM orchards and/or native sites. We did find significantly greater (P less than or equal to 0.05) densities of soil microarthropods early in growing s eason, June 1997 and April 1998, in the OM orchards in comparison to the CM orchards and native sites. Furthermore, the densities of predatory mites w ere significantly greater in the OM orchards in comparison to both the CM o rchards and native sites on selective dates throughout the period of study. Organic management practices have increased the densities of microarthropo ds above those found in CM orchards and native sites. These results may be due to the interaction between a greater accumulation of plant litter and o rganic matter in the OM orchards and the heavy pesticide use in the CM orch ards. (C) 2001 Elsevier Science B.V. All rights reserved.