Bongers, T. (1990). The maturity index: an ecological measure of environmental disturbance based on nematode species composition. Oecologia, 83(1), 14-19.

Once you identify the nematodes to family or genus, you assign the corresponding c-p value using the list proposed by Bongers and Bongers (1998) or Ferris (2010).

T. Bongers and M. Bongers (1998) Functional diversity of nematodes. Appl. Soil Ecol. 10.

Ferris, H. (2010) Form And function: metabolic footprints of nematodes in the soil food web. European Journal of Soil Biology 46, 97–104.

Sánchez-Moreno, S. and H. Ferris. 2018. Nematode ecology and soil health. In Plant Parasitic Nematodes in Subtropical and Tropical Agriculture. Sikora, R.A., D. Coyne, J. Hallmann and P. Timper (eds.). CAB International. Boston, USA. pp. 62-86.

You need to identify ALL your nematodes at family level, and even better at genus level; when you obtain guilds (Feeding type + succession position), you may start calculation of indices for bioindication

G. W. YEATES, 1 T. BONGERS, 2 R. G. M. DE GOEDE, 3 D. W. FRECKMAN, 4 AND

S. S. GEORGIEVA Feeding Habits in Soil Nematode Families and

Genera--An Outline for Soil Ecologists. Journal of Nematology 25(3):315-331. 1993.

Ferris H. 2010. Contribution of nematodes to the structure and function of the soil food web. Journal of Nematology, 42(1): 63–67.

Ferris H., Bongers T. and Goede De R.G.M. 2001. A framework for soil food web diagnostics: Extension of the nematode faunal analysis concept. Applied Soil Ecology, 18: 13–29. https://doi.org/10.1016/S0929-1393(01)00152-4

Howard Ferris may have some pages on his website worth digging into:

http://nemaplex.ucdavis.edu/Ecology/EcophysiologyParms/EcoParameterMenu.html

Howard Ferris' site also has a link to NINJA (Nematode INdicator Joint Analysis)https://shiny.wur.nl/ninja/

Here is a link to one of the papers Alexander Ryss referenced:

http://nemaplex.ucdavis.edu/FerrisPublications/pdf%20files/125FerrisBongersetal2001.pdf