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Compaction Alters Physical but Not Biological Indices of Soil Health

USDA Service Center, Pacific Southwest Research Station, 3644 Avtech Parkway, Redding, CA 96002

View larger version (50K): [in a new window]   Fig. 1. Bulk density of a clay loam and a sandy loam soil following manual compaction. Values are means (± s.e.; n = 16) of four replicates from four sampling dates (4, 11, 32, and 67 d after compaction). No statistical differences (Wald-Z test, = 0.05) were found between sampling dates for either soil.

View larger version (64K): [in a new window]   Fig. 2. Pore-size distribution determined from moisture retention curves. Rotated triangles represent volumetric water content during the experiment.

View larger version (27K): [in a new window]   Fig. 3. Effect of moderate and severe compaction on surface CO2 efflux. Values are means (n = 4) with standard error bars.

View larger version (32K): [in a new window]   Fig. 4. Compaction effects on carbon utilization profiles (Biolog) for both soils. Temporal change in average well color development (95 single carbon compounds) is presented (± s.e.; n = 4).

View larger version (23K): [in a new window]   Fig. 5. Principal component analysis results for both soils showing sample relationship to principal components.

View larger version (26K): [in a new window]   Fig. 6. Principal component analysis results for each soil showing coefficients of each PC and variable loadings on the first two components. All symbols represent standardized variables: Db = bulk density; Pt = total porosity; Ph = habitable porosity; Pa = air-filled porosity; efflux = CO2 efflux; resp = respiration; biomass = microbial biomass; Cuse = carbon source utilization; bact = total bacteria; fungi = fungal hyphae.

View larger version (17K): [in a new window]   Fig. 7. Soil strength and microbial biomass measurements show no relationship for two Long-term Soil Productivity Study sites in Northern California. Microbial biomass and soil strength were determined on samples collected within 2 cm of each other (n = 60 sample points per site) in the surface 15 cm.