Comparative Analysis of Nematode Community Structure of Neighboring Organic Carrot, Conventional Corn and Woodlot Soils

Relatively little is known about the differences in nematode community structure among comparative organic, conventional and woodlot systems. In addition, very little is known about the nematodes associated with the O-horizons of soil. The present research describes the nematode community structure associated with the O-horizon (litter layer), A-horizon (0-15 cm soil depth) and B-horizon (15-30 cm soil depth) of neighboring certified organic, conventional agricultural and woodlot soils. The sites are believed to be derived from similar soil parent material through similar processes but managed differently during the twenty years before the study. They exhibited, however, different physical and chemical characteristics, most likely due to management practices. Twenty-six nematode taxa were identified and partitioned into five trophic feeding groups. Eight of the taxa, Diphtherophora sp., Hemicycliophora sp., Criconemella sp., Xiphinema sp., Helicotylenchus sp., Rotylenchus sp., Hoplolaimus sp. and Tylenchorhynchus nudus were site specific. The nematodes recovered from the three soil horizons were associated with the sites, and each site had a different nematode community structure with regard to their O-, A- and B-horizons. The vast majority of nematodes recovered from the organic site were bacterivores, and fungivores associated with the O-horizon. The highest absolute population density of nematodes associated with the woodlot and conventional corn site were recovered from the A-horizon. The organic site had significantly fewer herbivores than the woodlot or conventional corn sites. The results show important differences in nematode community structure among the three systems. They also illustrate the importance of including nematodes from the O-horizon when evaluating the utility of nematode community structure as an indicator of soil health.