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Residue Carbon Stabilization in Soil Aggregates of No-Till and Tillage Management of Dryland Cropping Systems

^a Natural Resource Ecology Lab. and Dep. of Soil and Crop Sciences, Colorado State Univ., Fort Collins, CO 80523
^b Dep. of Natural Resources, Univ. of New Hampshire, Durham, NH 03824
^c Dep. of Earth and Atmospheric Science, Purdue Univ., West Lafayette, IN 47907
^d Dep. of Plant Sciences, Univ. of California, Davis, CA 95616

View larger version (10K): [in this window] [in a new window]   Fig. 1. Fractionation scheme for the isolation of aggregate size classes by wet sieving and macroaggregate disruption (Six et al., 2000a).

View larger version (21K): [in this window] [in a new window]   Fig. 2. Initial and final aggregate distributions for the first two depths (0–5 and 5–15 cm) of the tillage management (TM) and no-till (NT) treatments at Sterling, CO. The macroaggregate (macros), microaggregate (micros), silt plus clay (S+C), coarse particulate organic matter (cPOM), microaggregates within macroaggregates (mM), and silt plus clay within macroaggregates (minM) fractions are expressed in terms of grams per kilogram whole soil. Error bars represent ± one standard error of the mean. Different letters represent significant differences (Bonferroni's adjustment, = 0.05) within each sieving class among tillage treatment and depth increment. Uppercase and lowercase letters correspond to the TM and NT treatments, respectively. * Significant differences between the two tillage treatments within each aggregate class and depth combination.

View larger version (29K): [in this window] [in a new window]   Fig. 3. Final aggregate distributions for the tillage management (TM) treatment for each depth increment (0–5, 5–15, and 15–30 cm). The macroaggregate (macros), microaggregate (micros), silt plus clay (S+C), coarse particulate organic matter (cPOM), microaggregates within macroaggregates (mM), and silt plus clay within macroaggregates (minM) fractions are expressed in terms of the whole soil. Error bars represent ± one standard error of the mean. Aggregate proportions followed by a different uppercase letter within the depth increment or isolation method are significantly different; aggregate proportions followed by a different lowercase letter within an aggregate class are significantly different (Bonferroni's adjustment, = 0.05).

View larger version (35K): [in this window] [in a new window]   Fig. 4. Residue-derived C stabilization for the 0- to 5- and 0- to 15-cm depth increments of the tillage management (TM) and no-till (NT) treatments at Sterling, CO. The macroaggregate (macros), microaggregate (micros), silt plus clay (S+C), coarse particulate organic matter (cPOM), microaggregates within macroaggregates (mM), and silt plus clay within macroaggregates (minM) fractions are all expressed in terms of grams residue-derived C per kilogram soil per kilogram residue-derived C added. Error bars represent ± one standard error of the mean. Different letters represent significant differences (Bonferroni's adjustment, = 0.05) among each aggregate class within a sieving method and tillage treatment for each depth. Uppercase and lowercase letters correspond to the TM and NT treatments, respectively. * Significant difference between TM and NT within each aggregate class.

View larger version (28K): [in this window] [in a new window]   Fig. 5. Residue-derived C stabilization across the three depths (0–5, 5–15, and 15–30 cm) of the tillage management (TM) treatment at Sterling, CO. The macroaggregate (macros), microaggregate (micros), silt plus clay (S+C), coarse particulate organic matter (cPOM), microaggregates within macroaggregates (mM), and silt plus clay within macroaggregates (minM) fractions are expressed in terms of grams residue-derived C per kilogram soil per kilogram residue-derived C added. Error bars represent ± one standard error of the mean. Different letters represent significant differences (Bonferroni's adjustment, = 0.05) between the three depths within each aggregate class. For example, there was not a comparison made between macroaggregates and microaggregates for any depth. Uppercase and lowercase letters correspond to the wet sieving and macroaggregate-derived fractions, respectively.