Effects of long-term turfgrass management practices on soil nematode community and nutrient pools

The impact of long-term turfgrass management practices on soil nematode population and community structure and nutrient pools were studied in replicated Kentucky bluegrass (Poa pratensis) plots managed under 9 different organic- and mineral-fertilizer regimes for 15 years in Delaware, Ohio. Soil samples were collected in September 2003, July 2004 and October 2004. Nematodes were extracted using the Baermann funnel technique, identified to genus level, and populations of total, free-living (FLN), bacterivorous, fungivorous, predatory, omnivorous, and plant-parasitic (PPN) nematodes, were counted. FLN/PPN ratio, total number of genera, genus diversity, richness, evenness, Maturity Index, Plant-Parasitic Index, and Combined Maturity Index were calculated. In addition, soil nematode faunal profile analysis was conducted to determine soil food web condition using Enrichment Index and Structure Index. Concentrations of NH4-N, NO3-N, dissolved organic nitrogen, microbial biomass nitrogen, and soil organic matter (SOM) were measured in soil samples to describe soil nutrient status. Results from repeated measures analysis of variance showed that in general, nematode populations and food web indices were not differently affected by the 9 turfgrass management regimes but microbial biomass nitrogen and SOM were different. Further group analysis revealed that nematode community indices, Maturity Index and Combined Maturity Index, were significantly lower and Enrichment Index was significantly higher under high (223 kg N ha−1 year−1) and medium (171 kg N ha−1 year−1) N-input compared to low N-input (98 kg N ha−1 year−1) management group, indicating disturbance of the nematode food web. In addition, organic-fertilizer based turf management resulted in significantly higher soil microbial biomass compared to mineral-fertilizer management or the control, but no differences were found in the nematode community between the two fertilizer types. Herbicide, insecticide, or fungicide applications had no significant negative effect on soil nematode community, microbial biomass and SOM. We conclude that the amount of N fertilizer influences the soil nematode food web and nutrient pools in turfgrass while pesticides have no effect. Our results also show that irrespective of the management regime, the soil nematode food webs under turfgrass are more enriched but less structured than those under natural grassland ecosystems, indicating an overall food web disturbance.