Is duration of organic management reflected on nematode communities of cultivated soils?

The aim of this study was (a) to explore long-term responses of soil nematodes to the conversion from conventional to organic cultivation and (b) to differentiate them from the short-term responses to seasonal agricultural practices. Nematode communities were studied in terms of trophic and generic structure, life strategy and diversity, in asparagus cultivations along a gradient from conventional to organic under conversion (1 and 2 years), and certified organic (4 and 5 years). Samplings throughout the year were conducted with respect to seasonal agricultural practices. Changing management regime from conventional to organic cultivation seemed to initiate successional long-term changes in nematode communities, such as the gradual decline of phytoparasites in favour of bacterivores and fungivores, the gradual decrease of PPI, the increase of diversity. Alterations in the generic structure of the community were also revealed, driven mostly by the opposite trends of changes in abundance of Helicotylenchus vs. Heterocephalobus. Seasonal agricultural practices appeared to induce short-term responses of functional guilds of low colonizer-persister values (c-p I and 2) mostly, and were reflected in nematode indices, such as Maturity Index, Plant Parasitic Index, Enrichment Index, Channel Index but not Structure Index. Nematode responses at the generic level to seasonal agricultural practices seemed less intense than the ones imposed by changing management regime, and in the case of conventional cultivation they were almost entirely masked.