Soil nematode responses to crop management and conversion to native grasses.

Soil nematode community response to treatments of three, four-year crop rotations (spring wheat-pea-spring wheat-flax, spring wheat-green manure-spring wheat-flax, and spring wheat-alfalfa-alfalfa-flax) under conventional and organic management, and native tall grass restoration (restored prairie) were assessed in June 2003, and July and August 2004. The research site was the Glenlea Long-term Rotation and Crop Management Study, in the Red River Valley, Manitoba, established in 1992. The nematode community varied more with sample occasion than management and rotation. The restored prairie favored high colonizer-persister (c-p) value omnivores and carnivores, and fungivores but less bacterivores. The restored prairie soil food web was highly structured, mature and low-to-moderately enriched as indicated by structure (SI), maturity (MI) and enrichment (EI) index values, respectively. Higher abundance of fungivores and channel index (CI) values suggested fungal-dominated decomposition. Nematode diversity was low even after more than a decade of restoration. A longer time may be required to attain higher diversity for this restored fragmented prairie site distant from native prairies. No consistent differences were found between organic and conventional management for nematode trophic abundance, with the exception of enrichment opportunists of the c-p 1 group which were favored by conventional management. Although EI was lower and SI was higher for organic than conventional their absolute values suggested decomposition channels to be primarily bacterial, and fewer trophic links with both management scenarios. A high abundance of fungivores in the rotation including the green manure indicates greater fungal decomposition.