Short term effects of soil disinfection with metham sodium and organic alternatives on nematode communities

Nematode communities are valuable bioindicators of soil disturbance induced by agricultural practices. We report the results of a short term experiment set on a field previously cultivated with shell beans, where different agricultural practices were applied, namely disinfection with chemicals or organic alternatives (neem, basil, marigold and clove oils). We provide a detailed description of the soil nematode community before and after the application of agricultural practices, in terms of trophic structure, nematode functional indices and diversity. We also employ network analysis techniques to analyze the structure of nematode assemblages on the basis of co-occurrence of genera in samples. Chemical disinfection had a direct lethal effect on all nematode genera reducing or even eliminating their populations, while organic amendments favored only the free living nematodes without affecting plant feeders. These differences were poorly reflected on changes of diversity and even less on those of nematode indices. Network analysis offered significant insights into the structural changes in the web of interactions among nematode genera. The network after chemical disinfection was smaller, poorly connected and almost entirely dependent on the dominant phytoparasite Paratylenchus. In the absence of chemicals, large and more complex networks were formed