Composite soil samples consisting of either four 5-cm diameter cores (1987, 1989, 1994) or four to twenty 2.5-cm diameter cores (post 1994) were collected to a depth of 20 cm in a systematic pattern from each plot in June or October. Initial samples were collected in October 1987 and 1989, with subsequent sampling events occurring at approximately 5-year intervals. The final sampling occurred in June 2017.

Nematodes were initially extracted from 100 cm3 subsamples using a modified Christie-Perry technique (Christie and Perry, 1951) consisting of sieving followed by tissue extraction. Due to poor recovery of criconematid nematodes, the centrifugal flotation procedure (Jenkins, 1964) was used after 1994. Extracted nematodes were identified to genus and assigned a feeding habit based on Yeates, et al. (1993). A complete list of nematode genera and species present in the BGPE can be found in Darby, et al. (2013). Detailed methods and results from nematode-focused sampling in the BGPE are reported in Todd (1996), Jones, et al. (2006), and Darby, et al. (2013).

References
Christie, J.R., Perry, V.G., 1951. Removing nematodes from soil. Proc. Helminthol. Soc. WA 18, 106-108.

Darby, B.J., Todd, T.C., Herman, M.A., 2013. High-throughput amplicon sequencing of rRNA genes requires a copy number correction to accurately reflect the effects of management practices on soil nematode community structure. Mol. Ecol. 22, 5456–5471. https://doi.org/ 10.1111/mec.12480.

Jenkins W.R., 1964. A rapid centrifugal-flotation technique for separating nematodes from the soil. Plant Dis. Rep. 48, 692.

Jones, K.L., T.C. Todd, J.L. Wall-Beam, J.D. Coolon, J.M. Blair, and M.A. Herman.  2006.  Molecular approach for assessing responses of microbial-feeding nematodes to burning and chronic nitrogen enrichment in a native grassland.  Molecular Ecology 15:2601-2609.

Todd, T.C.  1996.  Effects of management practices on nematode community structure in tallgrass prairie.  Applied Soil Ecology 3:235-246.

Yeates, G.W., Bongers, T., de Goede, R.G.M., Freckman, D.W., Georgieva, S.S., 1993. Feeding habits in soil nematode families and genera - an outline for soil ecologists. J. Nematol. 25, 315-331.