Nematodes as bioindicators of soil food web health in agroecosystems: A critical analysis

Nematodes occupy a central position in the soil food web occurring at multiple trophic levels and, therefore, have the potential to provide insights into condition of the soil food webs. I hypothesized that differences in management strategies may have differential effects on nematode community structure and soil properties. This hypothesis was tested in three different replicated experiments. In the first study a conventional farming system receiving synthetic inputs was compared with an organically managed system and in the second study four different farming strategies with and without compost application transitioning to organic management were compared for nematode communities and soil characteristics including soil bulk density, organic matter, microbial biomass and mineral-N. The third study was aimed at assessing the indicative value of various nematode measures in five habitats. Nematode food webs were analyzed for trophic group abundance and by calculating MI, and enrichment (EI), structure (SI) and channel indices (CI) based on weighted abundance of c-p (colonizer-persister) guilds.; Bacterivore nematodes were more abundant in the organic than the conventional whereas the conventional system had higher population of the root lesion nematode, Pratylenchus crenatus compared with organic system. Organic hay plots had the lowest populations of P. crenatus compared to corn, soybeans and oats. Enrichment opportunists c-p 1 and general opportunists c-p 2 bacterivores were higher in composted than the non-composted strategies. Population of Pratylenchus sp. was significantly lower but that of c-p 2 plant parasites Tylenchus and Filenchus were higher in the composted compared with non-composted amended soils. Principal components analysis indicated that MI, SI and EI contributed the most to differences between the habitats. Forests and shrublands had highly structured food webs as expected but their high enrichment may be unique due to the muck soils. Croplands showed a clear distinction from other habitats with less structured food webs. Turfgrass lawns occupied an intermediary position between disturbed and unmanaged habitats. Lack of increase in SI in the organic farming system could be due to the high tillage requirement, which might have suppressed the population of high c-p value tillage-sensitive nematodes.