Management effects on epigeal arthropods and soil-dwelling communities during the transition to organic agriculture

Open Access
Author:
Jabbour, Randa
Graduate Program:
Ecology
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
November 12, 2008
Committee Members:
  • Mary Ellen Barbercheck, Dissertation Advisor
  • Mary Ellen Barbercheck, Committee Chair
  • Shelby Jay Fleischer, Committee Member
  • Nancy M Ostiguy, Committee Member
  • Katriona Shea, Committee Member
Keywords:
  • cover cropping
  • tillage
  • organic agriculture
  • entomopathogenic fungi
  • entomopathogenic nematodes
  • refuges
  • habitat complexity
  • dispersal
  • soil ecology
Abstract:
The growing demand for organic products exceeds supply, creating exciting opportunities for farmers. However, conventional farmers need to know the consequences of their management practices on the likelihood of successful conversion to organic production. Here, we explored management effects on epigeal and soil-dwelling arthropods and entomopathogens in feed-grain rotations during the transition to organic agriculture in central Pennsylvania. We examined the interaction between soil disturbance (full vs. reduce tillage) and initial cover crop management (timothy/clover vs. rye/vetch) on naturally occurring entomopathogenic fungi and epigeal arthropods during the three-year transition to organic production in a feed grain rotation in central Pennsylvania. Detection of Metarhizium anisopliae (Metschn.) Sorokin was variable between sampling dates and years. We detected M. anisopliae more frequently in the systems initiated with timothy/clover cover crops and utilizing full tillage; however, we only observed a tillage effect in the first temporal replicate. M. anisopliae detection was negatively associated with soil moisture and Zn, S, and Cu concentrations in the soil. Epigeal arthropod community composition was defined by initial cover crop in the first year in the transition sequence, by the interaction between cover crop and tillage intensity in the second year, and by tillage intensity in the final year. Spatial habitat complexity may conserve beneficial organisms in the soil. We compared the effect of simple (maize) and complex (maize plus mixed annual plant refuge) habitats on the dispersal of the entomopathogenic nematode, Steinernema carpocapsae (Weiser) (Sc). We showed that complex habitats can enhance dispersal, conditional on complex habitats conserving soil moisture in comparison to simple habitats. The maximum movement rate was 33.3 cm/day, which exceeds previously reported rates of 7.5 cm/day. We sampled soil microarthropod communities in simple and complex habitats in response to nematode application. Soil surrounding Sc-killed and freezer-killed insects contained more dipteran larvae, acarid mites, staphylinid beetle larvae, onychiurid and entomobryid collembolans, and immature and male mesostigmatid mites than soil at sham burial and no disturbance sites. Microarthropod communities were similar between simple and complex habitats. Tillage intensity, cover cropping, and increased habitat complexity do have implications for the occurrence and activity of natural enemies during the transition to organic. Farmers can use this information when assessing the costs and benefits of competing strategies, dependent on their site-specific challenges.