Interest in the sustainability of farming practices has increased in response to environmental problems associated with conventional agricultural management often adopted for the production of ...herbaceous, ornamentals, and fruit crops. Availability of measures of the status of the soil ecosystem is of immediate importance for environmental assessment and monitoring programs, as well as for farm managers who could timely modify their farming practices. This study investigated the effects of various agricultural management regimes comparing standard vs. reduced practices (irrigation rates, fertilization rates, and types of ground cover) on the structure of nematode fauna in a citrus orchard in the sandy ridge area of Central Florida. Ecological measures such as community structure indices, diversity indices, and maturity indices were assessed and related to different agricultural regimes. From the various indices of community structure, maturity indices were most effective in distinguishing differences between agricultural regimes. In an irrigation experiment (six irrigation rates), maturity indices could indicate history of water usage. In a multifactorial experiment (two fertilization levels, two irrigation levels, and two type of ground cover), maturity indices, unlike diversity indices, indicated the status and intensity of soil processes (decomposition, mineralization). Maturity indices were also the only measures at the index level responding consistently and significantly to fertilizer rates. Overall, maturity indices can provide sufficient information and thus prove to be efficient tool for quick estimates of the soil condition. Trophic groups might be useful in describing general and overall trends of the soil ecosystem status, however, this level of resolution is not recommended for monitoring purposes. Trophic grouping averages different, sometimes opposite, nematode responses observed at the generic level. Therefore, the most accurate and indicative information about the status and intensity of the soil processes is provided by characterization of the nematode community at the generic if not species level. The effects of farming practices on the status of macro- and micronutrients in the soil and on sustainability measures were also examined, and related to nematode components of the soil citrus ecosystem. Some nematode measures related to several components of sustainability and soil chemical measures.
In January 2001, we surveyed streams and ponds above 300 m a.s.l. in Taylor Valley, South Victoria Land, Antarctica. One pond was examined in detail. Organic materials covered nearly 100% of the ...adjacent soil to 5-20 m from the shore, with intermittent patches to 80 m. Organic matter averaged 257 g C/m^sup 2^, and totaled 1,388 kg organic C on the soil around the pond. Soil-moisture content (0.56-12.41%) decreased with distance from shore, whereas pH (7.8-10.8) increased with distance. Electrical conductivity was lowest in the soils <10 m from the pond (416±94 µS/cm). Mineral soil organic C and total N concentrations were greatest between 10 and 30 m from the edge of the pond (1.21±0.37 and 0.13±0.05 mg/g soil, respectively). Soil invertebrates were present in only 50% of samples and included tardigrades, rotifers, and two nematodes, Scottnema lindsayae and Plectus antarcticus. A non-parametric, discriminant function analysis based on soil moisture, soil organic carbon, and electrical conductivity correctly predicted 87.0% of sites that had invertebrates and 70.8% of sites for which invertebrates were absent. Tardigrades, rotifers, and P. antarcticus were found only in the wettest soils nearest the pond whereas S. lindsayae was restricted to drier soils further from shore. Other ponds and streams also showed substantial accumulations of organic matter, suggesting that upland wetlands serve as resource islands in these polar deserts that provide a source of organic matter to nearby soils.PUBLICATION ABSTRACT
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