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 the Western Slope of Colorado. The 'organic' orchards differed from the 'conventional' orchards in that they used natural fertilizers (versus synthetic) and did not use insecticides and/or herbicides. Based on findings from annual agroecosystems, we hypothesized that the conventionally managed (CM) apple orchards would support a lower diversity and density of soil microarthropods than the organically managed (OM) apple orchards. We located nine sites, three OM orchards, three CM orchards, and three native sites. From each site, microarthropods were extracted from soil samples taken from June to September of 1997 and April to September of 1998. The richness and diversity 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 season, June 1997 and April 1998, in the OM orchards in comparison to the CM orchards and native sites. Furthermore, the densities of predatory mites were significantly greater in the OM orchards in comparison to both the CM orchards and native sites on selective dates throughout the period of study. Organic management practices have increased the densities of microarthropods 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 organic matter in the OM orchards and the heavy pesticide use in the CM orchards. (C) 2001 Elsevier Science B.V. All rights reserved.