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Soil Water Hysteresis in Water-Stable Microaggregates as Affected by Organic Matter

^a Institute for a Secure and Sustainable Environment, Center for Environmental Biotechnology, Dep. of Earth and Planetary Sciences, Univ. of Tennessee, Knoxville, TN 37996
^b Darling Marine Center, Univ. of Maine, Walpole, ME 04573
^c Biosciences Division, Argonne National Lab., Argonne, IL 60439

View larger version (11K): [in this window] [in a new window]   Fig. 1. Validation of the model on the measured drying and wetting data of water characteristics.

View larger version (27K): [in this window] [in a new window]   Fig. 2. Management practice effects on predicted water characteristics of soil microaggregates. Note that the scale of the y axis for Kentucky soils is different from that for Fermilab soils. In (A) and (B), VP = virgin prairie, RP = restored prairie, and Cult = cultivated land. In (C) and (D), CT = conventional tillage, NT = no-till, 0 and 336 are N-fertilization treatments (kg N ha–1). Intercept and slope comparisons among treatments derived from significant analysis of covariance results followed by multiple Bonferroni-corrected Student's t-tests are given in parentheses after legend entries; the intercepts of treatments followed by the same lowercase letter and the slopes of treatments followed by the same uppercase letter were not significantly different at P < 0.05.

View larger version (9K): [in this window] [in a new window]   Fig. 3. (A and B) Difference in water content between the drying and wetting curves (g,d – g,w), and (C) the correlation between organic C (OC) content and g,d – g,w at 1 MPa. In (A), VP = virgin prairie, RP = restored prairie, and Cult = cultivated. In (B), CT = conventional tillage, NT = no-till, 0 and 336 are N-fertilization treatments (kg N ha–1). For (A) and (B), intercept and slope comparisons among treatments derived from significant analysis of covariance results followed by multiple Bonferroni-corrected Student's t-tests are given in parentheses after legend entries; the intercepts of treatments followed by the same lowercase letter and the slopes of treatments followed by the same uppercase letter were not significantly different at P < 0.05.

View larger version (23K): [in this window] [in a new window]   Fig. 4. (A–D) Organic matter (OM) removal effect on the drying and wetting curves of microaggregates of three choronsequence soils, and (E and F) the agreement between the OM-filled pore volume (measured using small-angle x-ray scattering technique [McCarthy et al., unpublished data, 2005]) and the decrease in water content resulting from OM removal (measured using water retention method). In (A) and (B), results of analysis of covariance (ANCOVA) comparisons of intercepts and slopes are indicated below the legend. For (C) and (D), intercept and slope comparisons among treatments derived from significant ANCOVA results followed by multiple Bonferroni-corrected Student's t-tests are given in parentheses after legend entries; the intercepts of treatments followed by the same lowercase letter and the slopes of treatments followed by the same uppercase letter were not significantly different at P < 0.05.The error bars in (E) and (F) indicate the standard deviations of combustion-induced water content change across a range of water tension from 0.1 to 44 MPa.

View larger version (8K): [in this window] [in a new window]   Fig. 5. Organic matter removal effect on the difference in water content between the drying and wetting curves (g,d – g,w) of three Fermilab chronosequence soil microaggregates. Results of analysis of covariance comparisons of intercepts and slopes are indicated below the legend. OC = organic C.