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Edaphic Controls on Soil Organic Carbon Retention in the Brazilian Cerrado: Soil Structure

^a School of Natural Resources, Ohio State Univ., 2021 Coffey Rd., Columbus, OH 43210-1085
^b Embrapa Cerrados Agric. Research Center, P.O. Box 08223, 73310-970, Planaltina-DF, Brazil

View larger version (25K): [in this window] [in a new window]   Fig. 1. Organic C and aggregation in soil profiles: (a) mean bulk soil organic C concentration; and (b) mean weight diameter of water-stable aggregates. Bars represent standard error (n = 3).

View larger version (30K): [in this window] [in a new window]   Fig. 2. Linear relations between mean weight diameter and (a) clay + silt contents in bulk soil and (b) soil organic C concentration for 10 depths.

View larger version (31K): [in this window] [in a new window]   Fig. 3. Soil organic C (SOC) concentration in individual water-stable aggregate size classes corrected for mineral sand and particulate organic matter in three selected soil depths. Bars represent standard error (n = 3).

View larger version (20K): [in this window] [in a new window]   Fig. 4. Graphic depiction of the soil organic C (SOC) dilution effect in sand-free water-stable aggregates (WSA, mean of five size classes) as a function of clay + silt contents in bulk soil (n = 9 for each depth).

View larger version (112K): [in this window] [in a new window]   Fig. 5. S-matrix and coarse to fine (c/f) distribution of pedogenic water-stable aggregates >2 mm, 0- to 5-cm depth: (a) Quartzipsamment—note dark, isotropic plasma and large packing voids; b) sandy Haplustox—note dark, isotropic plasma; (c) loamy Haplustox—note hollow root remains and surrounding void; and (d) clayey Haplustox—note opaque nodules. All images between crossed polars, except for (d) (plane polarized light).

View larger version (26K): [in this window] [in a new window]   Fig. 6. Total free and occluded particulate organic matter (POM) C of selected soil depths (a) as a percentage of total soil organic C (SOC), and (b) in absolute units. Bars represent standard error (n = 3).

View larger version (22K): [in this window] [in a new window]   Fig. 7. Linear relation between free POM C percentage and clay content for the combined 0- to 5-, 30- to 40-, and 90- to 100-cm depths (R2 = 0.74, n = 27). Dotted line is 95% confidence interval.

View larger version (94K): [in this window] [in a new window]   Fig. 8. Loamy Haplustox, 0- to 5-cm depth (detail of Fig. 5c): occluded particulate organic matter as a partially decomposed root. Note adhesion of soil particles to root surface (between crossed polars).

View larger version (38K): [in this window] [in a new window]   Fig. 9. Mean C/N ratio of occluded particulate organic matter (POM) of sand fractions from dispersed water-stable aggregate size classes of selected soil depths. Bars represent standard error (n = 3).

View larger version (102K): [in this window] [in a new window]   Fig. 10. Faunal peds in water-stable aggregates >2 mm, 0- to 5-cm depth: (a) loamy Haplustox, aggrotubule; (b) clayey Haplustox, fecal pellet; (c) Quartzipsamment, cocoon (a–c, in oblique incident light); and (d) clayey Haplustox, detail of aggrotubule with unknown euhedral crystal (between crossed polars). Scale in millimeters.