Are community structures of soil nematodes different between organic and conventional farming systems in commercial tomato fields?

摘要

Compared with studies conducted in experimental crop fields, those in commercial fields have been very limited to examining how organic (ORG) and conventional (CONV) farming systems differ in their effects on biological and physicochemical characteristics of soils. To evaluate practical effects of ORG systems, a comparison is essential with "practical" CONV systems where organic amendments are also used in addition to chemical fertilizers and pesticides. We compared nematode community structures between the two systems for commercial tomato production in greenhouses located in northern Japan in 2005 and 2006. We examined if the farming system was still influential even when differences in soil texture, study plot locations and- growing seasons amongthe plots were considered. The density of the predator-omnivore group, with Dorylaimida as the dominant taxon, and Structure Index were always significantly affected by farming system, and their values were greater in ORG. Redundancy analysis in 2005 revealed that farming system could significantly explain the whole community structure, and determined Dorylaimida as an indicator for ORG, while Diplogasteridae and Anguinidae were indicators for CONV. Although redundancy analysis could not significantlyexplain community structure with farming system in 2006, Dorylaimida and Diplogasteridae were still good indicators for the two systems. Individual variables, such as soil texture and bacterial density, were found to have significant effects on the two nematode taxa, although we could not interpret sufficiently the causal relationships. Further studies should include other measurements such as chemical pesticides applied for better interpretation of the differences between these systems.