Soil nematode community changes associated with compost amendments

Abstract Five composts (C1: fresh olive pomace, straw, chicken manure, urea; C2: fresh olive pomace, lettuce residues, cow manure, straw, sawdust; C3: sewage sludge, municipal green residues; C4: grass, leaves, tree branches, soil; C5: by-product from penicillin production (mycelium), straw and sawdust) were tested in a pot experiment to investigate their short-term effect on the nematode community of a grassland soil. Composts were mixed with soil at the rates of 10, 25, 50 and 100 g (kg soil)–1 and barley was sown in each potting mixture after a 2-month decomposition period. Nematodes were extracted from each pot 5 months after barley sowing, identified at genus level and grouped into bacterial, fungal and root fungal feeders, predators, omnivores and plant parasites. Bacterial feeders, predators and omnivores were favoured by amendments with composted penicillin substrate and partly by compost from olive pomace, whereas composts from green wastes and sewage sludge suppressed these trophic groups except for predators. All compost treatments suppressed fungal feeders as well as significantly reducing the density of plant-parasitic nematodes compared with non-amended soil. The highest suppressiveness on plant-parasitic nematodes was found for the composts from urban green residues, penicillin substrate and olive pomace plus cow manure. Suppressive effect was hypothesised to be related to ammoniacal nitrogen content of the composts. Composts from fungal mycelium or olive pomace seem to be the most suitable for application in nematode management strategies due to their low impact on beneficial trophic groups.