Submitted to: Plant and Soil
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/29/2006
Publication Date: 8/15/2006
Citation: Wang, K., Mcsorley, R., Burelle, N.K. 2006. Effects of cover cropping, solarization, and soil fumigation on nematode communities. Plant and Soil Journal. 286:229-243. DOI 10.1007/s11104-006-9040-4. Interpretive Summary: The effects of several soil management strategies on nematode community structure were evaluated in a two-year field experiment. Treatments consisted of methyl bromide + chloropicrin, solarization (S) for 6 weeks, cowpea (Vigna unguiculata) cover cropping for 3 months (CP), combination of solarization and cowpea cover cropping (S+CP), and a control (C) consisting of weedy fallow throughout the summer. Treatments were evaluated for the level and duration of perturbation to nematode community structure when bell pepper was planted in the fall following these treatments. Responses of nematode communities to soil treatments were most apparent immediately following all summer treatments (Pi) rather than at 4 months after the summer treatments (Pf). Perturbation from soil treatment based on nematode community studies in general followed the hypothetical trend of MB > S > S+CP > CP > C. Omnivorous nematodes were the most sensitive nematode trophic group, with impact from soil treatment lasting until the end of the pepper crop in both years. Nematode community indices such as F/(F+B), richness, and SI were also good bioindicators of these soil perturbations. While disturbance from MB on the nematode communities lasted at least until the end of the subsequent pepper crop, that from the solarization often disappeared after pepper planting. Growing a cover crop of CP enhanced many of the beneficial nematodes involved in nutrient cycling but fail to reduce the population densities of herbivorous nematode at pepper harvest. Combining CP and S reduced the perturbation from S on nematode communities, while achieving a suppression of Meloidogyne spp. equivalent to MB at crop harvest. In addition to the experimental soil treatments, application of glyphosate, and a disease epidemic following hurricanes in 2004 acted as additional sources of perturbation to nematode communities, possibly due to their impact on root biomass or organic matter in the soil.
Technical Abstract: While free-living nematodes play important roles in soil nutrient cycling, many pre-plant soil practices act as perturbations to nematode communities. A two-year field experiment was conducted to examine nematode communities in soil treated with methyl bromide (MB) fumigation, solarization (S) for 6 weeks, cowpea (Vigna unguiculata) cover cropping for 3 months (CP), combination of solarization and cowpea cover cropping (S+CP), and a control (C) consisting of weedy fallow throughout the summer. In general, responses of nematode communities to soil treatments were more obvious at termination of all summer treatments (Pi) than at 4 months after the summer treatments (Pf). In 2003, total abundance of bacterivores and fungivores followed a hypothesized pattern, with MB, S, and S+CP having greater impact on the community as compared to C and CP. However, this perturbation did not persist after a cycle of vigorous growth of a pepper crop in 2003. Abundance of omnivorous nematodes was enhanced by CP at Pi, and impact of soil treatment on this group of nematodes lasted to Pf in 2003, while impact on predatory nematodes was variable. Major differences between results in 2004 from 2003 were that the C treatment did not support the greatest numbers of free-living nematodes at Pi and a more severe impact of MB compared to S and S+CP resulted in 2004. While disturbance from MB on the nematode communities lasted at least until the end of the subsequent pepper (Capsicum annuum) crop, that from the solarization often disappeared after pepper planting. Growing and incorporating a cowpea cover crop enhanced many of the beneficial nematodes involved in nutrient cycling but failed to reduce the population densities of herbivorous nematodes at pepper harvest. Several indices of nematode community structure, especially richness, structure index, and ratio of fungivores to bacterivores, were especially useful in detecting trends in perturbation by the various soil treatments.