" Site rank for oribatid mite populations. b Abundance of individuals collected. 0 Total number of oribatid mite species identified. d Pielou's evenness index. e Shannon-Wiener biodiversity index. After Lamoncha and Crossley, 1998; from Knoepp, 2000.
uated in two different watersheds) exist. There is ample room for further investigation in this important area in which scientists and managers from a variety of disciplines will collaborate. This is especially true when comparisons are made across wide continental gradients, for example, across ecoregions.
The foregoing examples involved very extensive sampling and analytical regimes that might preclude their wide adoption in soil quality studies. An innovative study in Nebraska employed the fact that differences in electromagnetic (EM) soil conductivity and available nitrogen levels over a growing season can be linked to feedlot manure/compost application and use of a green winter cover crop (Eigenberg et al., 2002). A series of soil conductivity maps of a research cornfield were generated using global positioning system (GPS) and EM induction methods. The study was conducted over a 7-year period. Image processing techniques were used to establish EC treatment means for each of the growing season surveys. Sequential measurement of profile weighted soil electrical conductivity (ECa) was effective in identifying the dynamic changes in available soil nitrogen as affected by animal manure and nitrogen fertilizer treatments during the corn-growing season. This real-time monitoring approach shows considerable promise in enabling farmers to more efficiently use nitrogen sources in cropping management systems and in minimizing nitrogen losses to the environment.
It is imperative to have a robust, quantitative, and universally applicable metric for soil quality. Considering the 4.5 x 109 hectares that are tropical soils, use of an updated fertility capability soil classification (FCC) system (Sanchez et al., 2003) should be helpful for soil ecologists.
It employs quantitative topsoil attributes including percentage of total organic carbon saturation (van Noordwijk et al., 1998) compared with undisturbed or productive site and soil taxonomy. The top three soil constraints in the tropics include moisture limitations, low nutrient capital reserves, and high erosion risk. Because many small farmers in tropical regions depend on organic sources for nutrient inputs to their crops, this becomes an ideal situation to practice sound organic agriculture. This approach has been promoted ably by the Tropical Soil Biology and Fertility Programme, which has a network of research sites throughout eastern and southern Africa, India, and southeast Asia (see van Noordwijk etal., 1998, and Swift, 1999, cited in Sanchez etal., 2003, and Palm etal., 2001).
For those who are interested in pursuing practical, hands-on studies in soil ecology, Chapter 9 contains some selected field and laboratory exercises that should be of use in both research and teaching activities.
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