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This article in SSSAJ

  1. Vol. 75 No. 2, p. 580-590
    Received: Jan 18, 2010

    * Corresponding author(s): dpcollins@wsu.edu


Farm-Scale Variation of Soil Quality Indices and Association with Edaphic Properties

  1. Douglas P. Collins *a,
  2. Craig G. Coggerb,
  3. Ann C. Kennedyc,
  4. Thomas Forged,
  5. Harold P. Collinse,
  6. Andrew I. Baryf and
  7. Richard Rossig
  1. a Small Farms Program, Washington State Univ., Center for Sustaining Agric. and Natural Resources 2606 W. Pioneer, Puyallup, WA 98371
    b Crop and Soil Sciences, Washington State Univ., Puyallup Res. and Ext. Center Puyallup, 2606 W. Pioneer, Puyallup, WA 98371
    c USDA-ARS, Washington State Univ., 215 Johnson Hall, Pullman, WA 99164
    d Agriculture and Agri-Food Canada, P.O. Box 1000, Agassiz, BC, V0M 1A0 Canada
    e USDA-ARS, Washington State Univ., 24106 N. Bunn Rd., Prosser, WA 99350
    f Crop and Soil Sciences, Washington State Univ., Puyallup Res. and Ext. Center Puyallup, 2606 W. Pioneer, Puyallup, WA 98371
    g Newmont Mining Corp., Phoenix Mine P.O. Box 1657 Battle Mountain, NV 89820


Farm-scale variation of soil quality indices and association with edaphic properties. Soil organisms can be used as indicators of dynamic soil quality because their community structure and population density are sensitive to management changes. However, edaphic properties can also affect soil organisms and spatial variability can confound their utility for soil evaluation. We evaluate the relationship between two important agronomic functions, N-mineralization potential and aggregate stability, and biological, chemical, and physical edaphic properties. Decomposers, nematodes, collembolans, total C, total N, pH, bulk density (Db), and texture were evaluated at 81 sites across 25-ha of an organic farm in western Washington. We built regression trees with biological, chemical, physical, and management parameters to explain the farm-scale variation in microbial biomass (r 2 = 0.74), nematode density (r 2 = 0.61), collembolan density (r 2 = 0.36), nematode structure index (SI, r 2 = 0.41), nematode enrichment index (EI, r 2 = 0.54), proportion of soil as aggregates > 0.25 mm (r 2 = 0.60) and N-mineralization potential (r 2 = 0.58). Soils with microbial biomass > 597 μg Cmic g−1 formed a homogeneous group with the greatest N-mineralization potential, and soils with >13.5% clay formed a homogeneous group with the greatest proportion of soil aggregates > 0.25 mm. Increased soil aggregation was associated with larger nematode SI, though much of the variability in SI remained unexplained by the data. Tillage had a strong effect on both decomposer and nematode populations; soils not tilled for 5 yr had the largest microbial biomass and soils not tilled 2 wk before sampling had the largest nematode populations. Comparisons of soil quality indicators across farms should be sensitive to the association of indicators with soil texture and recent management practices.

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