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Tillage and Cover Cropping Effects on Aggregate-Protected Carbon in Cotton and Tomato

^a Dep. of Agronomy, 1025 Agronomy Hall, Iowa State Univ., Ames, IA 50011
^b Dep. of Land, Air and Water Resources, Univ. of California, Davis, CA 95616-8627
^c Dep. of Plant Sciences, Univ. of California, Davis, CA 95616

View larger version (33K): [in this window] [in a new window]   Fig. 1. Total C in the 0- to 15- and 15- to 30-cm depths for conservation (Cons.) and standard (Std.) tillage with and without cover cropping. Background lines represent the 1999 mean total C from across the field for each depth. Error bars represent standard error of the mean (n = 8). Bars not associated with the same letter are significantly different at P = 0.05.

View larger version (30K): [in this window] [in a new window]   Fig. 2. Total mass of C in each organic matter fraction after 5 yr of conservation (Cons.) or standard (Std.) tillage with or without cover cropping (LF = light fraction). Error bars represent standard error of the mean (n = 8). Bars not associated with the same letter are significantly different at P = 0.05.

View larger version (37K): [in this window] [in a new window]   Fig. 3. Percentage of added cotton C (13C) recovered in the organic matter fractions light fraction (LF), intraaggregate light fraction (iLF), and mineral-associated C (mC), by tillage treatment (Cons. = conservation, Std. = standard) and depth. Error bars represent standard error of the mean (n = 8). Bars not associated with the same letter are significantly different at P = 0.05. There were no significant differences in iLF among the treatments.

View larger version (35K): [in this window] [in a new window]   Fig. 4. The amount of added 13C derived from new cotton residue as a fraction of total C in the organic matter fractions light fraction (LF), intraaggregate light fraction (iLF), and mineral-associated C (mC), with respect to tillage treatment (Cons. = conservation, Std. = standard) and soil depth. Error bars represent standard error of the mean (n = 8). Bars not associated with the same letter are significantly different at P = 0.05. There were no significant differences in mC among the treatments.

View larger version (39K): [in this window] [in a new window]   Fig. 5. Amount of new cotton C (13C) as a fraction of total C found in the organic matter fractions light fraction (LF), intraaggregate light fraction (iLF), and mineral-associated C (mC), and the percentage of added 13C that was recovered, by date, tillage treatment, and cover crop treatment. Error bars represent standard error of the mean (n = 8). Bars not associated with the same letter are significantly different at P = 0.05. There were no significant differences in the recovery percentage of 13C in iLF among the treatments.

View larger version (37K): [in this window] [in a new window]   Fig. 6. Root and shoot C dynamics. Amount of new cotton C (13C) as a fraction of total C found and percentage of added 13C recovered in the organic matter fractions light fraction (LF), intraaggregate light fraction (iLF), and mineral-associated C (mC), by date, tillage treatment (Cons. = conservation, Std. = standard), and root or shoot treatment. Error bars represent standard error of the mean (n = 8). Bars not associated with the same letter are significantly different at P = 0.05. There were no significant differences in recovery percentage of 13C in iLF among the treatments.