The Indicator

The Nematode Maturity Index (NMI) is a weighted mean frequency of taxa assigned weights ranging from 1 to 5, with a smaller weight being assigned to taxa with relative tolerance to disturbance and a larger weight to taxa that are more sensitive to disturbance. The index combines both free-living and plant-parasitic nematodes but excludes taxa that simply respond ephemerally to added nutrients. This index can detect differences among fields in a regional survey more reliably than one that measures only free-living nematodes (Neher and Campbell 1996). (See references for a variety of publications that support the use of soil organisms, particularly nematodes, as indicators of soil quality.)

This index is based on the principle that different taxa have different sensitivities to stress or disruption of the successional sequence because of differences in their life history characteristics. Because succession may be disrupted at various stages by common agricultural practices, such as cultivation and applications of fertilizer and pesticides, the successional status of a soil community may reflect the history of disturbance. However, although a disturbance, such as the addition of animal manure to soil, initially produces a predominance of nematodes with smaller values, the abundance of nematodes with large maturity index values soon increases.

Maturity indices have the strength of responding to a variety of land management practices across plant species, soil types, and seasons (Neher et al. 1995). Nematode community structure and function are known to change in response to land management practices such as nutrient enrichment through fertilization by organic or inorganic nitrogen, cultivation, liming, and drainage, as well as to changes in plant community composition and age and to toxic substances such as heavy metals, pesticides, and petroleum products.

The Data Gap

Sampling should be carried out in autumn after cultivation of fields harvested in the fall; this will minimize within-field sampling variation. Free-living nematode populations are generally at their peak at this time because crop residues are incorporated into soil by cultivation and temperatures are moderate.

Cobb’s sieving and sugar centrifugal-flotation methods are recommended to optimize recovery of entire nematode communities from soil (Neher et al. 1995). Neher et al. (1998) suggest that it is unnecessary to calibrate indices of nematode community structure at a scale finer than the USDA’s Land Resource Regions.

References

Bernard, E.C. 1992. Soil nematode biodiversity. Biology and Fertility of Soils 14:99–103.

Blair, J.M., P.J. Bohlen, and D.W. Freckman. 1996. Soil invertebrates as indicators of soil quality, pp. 273–291. In Methods for assessing soil quality. Soil Science Society of America Special Publication 49, Madison, WI.

Freckman, D.W. 1998. Bacterivorous nematodes and organic-matter decomposition. Agric. Ecosystems Environ. 24:195–217.

Gupta, V.V.S.R., and G.W. Yeates. 1997. Soil microfauna as bioindicators of soil health, pp. 201–203. In C. Pankhurst, B.M. Doube, and V.V.S.R. Gupta (eds.), Biological indicators of soil health. New York: CAB International.

Hendrix, P.F., R.W. Parmelee, D.A. Crossley, Jr., D.C. Coleman, E.P. Odum, and P.M. Groffmann. 1986. Detritus food webs in conventional and no-tillage agroecosystems. BioScience 36:374–380.

Hunt, H.W., D.C. Coleman, E.R. Ingham, R.E. Ingham, E.T. Elliot, J.C. Moore, S.L. Rose, C.P.P. Reid, and C.R. Morley. 1987. The detrital food web in shortgrass prairie. Biology and Fertility of Soils 3:57–68.

Neher, D.A., and C. L. Campbell. 1996. Sampling for regional monitoring of nematode communities in agricultural soils. Journal of Nematology 28:196–208.

Neher, D.A., K.N. Easterling, D. Fiscus, and C.L. Campbell. 1998. Comparison of nematode communities in agricultural soils of North Carolina and Nebraska. Ecological Applications 8:213–223.

Neher, D.A., S.L. Peck, J.O. Rawlings, and C.L. Campbell. 1995. Measures of nematode community structure for an agroecosystem monitoring program and sources of variability among and within agricultural fields. Plant and Soil 170:167–181.

Yeates, G.W., and T. Bongers. 1999. Nematode diversity in agroecosystems. Agriculture Ecosystems & Environment 74:113–135.