NEMATODE COMMUNITY STRUCTURE AND CHEMICAL AND PHYSICAL PROPERTIES IN DIFFERENT TEXTURAL CLASSES OF SOIL IN THE ROOT ZONE OF 'WILLIAMS' PEAR

Nematode community structure depends on a number of factors including soil type and the crop grown and may shift from year to year depending on the site’s cropping history. The aims were to: describe the nematode community, relate soil properties and nematode assemblage and evaluate several ecological indices in two commercial pear orchards with different textural classes, in Upper Río Negro Valley. The soil type at site 1 (H1) was a loam (19.2% clay, 34.88% sand, 45.7% silt) and the soil type at site 2 (H2) was a clay loam (27% clay, 31.96% sand, 41.08% silt). Soil samples were collected in spring 2008 and autumn 2009 to determine soil properties and ecological measures of soil nematode community structure such as total abundance, trophic diversity, trophic group proportions, enrichment index and structure index. Loamy-textured soil had more nematode densities. Obligate plant feeders and bacterivorous nematodes were the most abundant trophic group in H1, averaging 30 and 26% of the nematode community, respectively, while bacterivorous and fungivorous were in H2, averaging 47 and 18%, respectively. The trophic diversity index was greater for H1, indicating greater evenness and greater numbers of the group trophic. All sites showed moderately enriched food webs as indicated by the mean enrichment index (EI) values (64-69). The structure index was consistently greater in H1, suggesting there was a change in function of diversity of the soil food web. Population densities of obligate plant feeders and omnivores-predators nematodes were negatively correlated with percentages of clay. Several soil chemical measures (Na+, K+) were related to several trophic groups.