Influence of farming practice, crop type and soil properties on the abundance of Enchytraeidae (Oligochaeta) in Greek agricultural soils

Abstract

Little information is available on the distribution of soil organisms such as enchytraeids in Greek agricultural soils. Therefore the aim of this work was to study their population densities under different farming practices, in different regions, and in relation to physico-chemical soil properties such as texture, pH, organic matter content, C:N ratio, and total copper content in soil. Soil samples were taken from 380 sites located in 18 regions all over Greece, but only data from 120 sites in 9 regions were appropriate for statistical evaluations. At each site soil samples were taken once, transported to the laboratory and kept there at 20°C and at a moisture of 40–50 % WHC for six weeks. Enchytraeids were extracted from the soils by a wet extraction method and counted. Species composition was determined in a few samples, revealing species of the genera Fridericia and Enchytraeus. Enchytraeids were absent from many soil samples which may be caused by the fact that many soils in Greece have a xeric moisture regime, conditions that are unfavourable to soil organisms. Highest abundances (about 14 000 ind. m-2) were recorded at olive groves and vineyard sites in mainland regions. Lowest abundances were recorded on islands such as Santorini, where no enchytraeids were detected in 13 out of 17 samples. Statistical analyses revealed significant differences of enchytraeid abundance among crop types (higher in olive than in vineyards or citrus) but not among farming practices or soil properties, including copper content. Sites with the same crop located in different regions differed in enchytraeid abundance in the case of olive groves and vineyards but not in citrus orchards. Total copper content was significantly higher in citrus orchards than in the other two crop types, but the determined copper levels were generally below those considered to harm oligochaetes. Further sampling using standard methods while addressing the species level are needed to reveal details of enchytraeid distribution, species composition and their ecological role in Greek soils.