Dynamics of nematode communities in tomatoes grown in conventional and organic farming systems, and their impact on soil fertility

Nematode communities were monitored intensively through a tomato (Lycopersicon esculentum L.) growing season in plots managed by conventional and organic farming practices. The temporal dynamics of individual species of bacterial-feeding nematodes differed and suggested differing importance of species in their contribution to N-mineralization in the organically managed soil. Species with r-selected, colonizer characteristics were most responsive to incorporation of organic matter and the subsequent increase of microbial biomass. Bacterial-feeding nematode populations were lowest early in the growing season, when tomato plants exhibited symptoms of nitrogen deficiency. We hypothesize that increasing abundance, biomass and activity of these nematodes in the spring by organic matter incorporation at the end of the previous crop would reduce the observed nitrogen stress. Fungal-feeding nematodes were more abundant in the conventional than the organic plots during periods of organic matter decomposition, possibly related to the higher carbon:nitrogen ratios of the crop residues incorporated into the conventional soils than of the manures and leguminous cover crops incorporated into the organic soils. Predaceous and omnivore nematode populations were low in both farming systems, and plant-parasitic nematode species reflected the crop sequences in rotations used in each system.