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Early Response of Soil Organic Fractions to Tillage and Integrated Crop–Livestock Production

USDA-ARS, Natural Resource Conserv. Center, 1420 Experiment Station Rd., Watkinsville, GA 30677

View larger version (10K): [in this window] [in a new window]   Fig. 1. Clay and sand concentration at the end of 1 yr as affected by tillage management. * Significant at P 0.05. ** Significant at P 0.01. *** Significant at P 0.001.

View larger version (16K): [in this window] [in a new window]   Fig. 2. Depth distribution of soil bulk density as affected by year, tillage, and cover crop management. Error bars denote significance (P = 0.05) among tillage and cover crop management variables within a depth and year of sampling. Depth of conventional tillage was initially 25 to 30 cm with a moldboard plow and thereafter 15 to 20 cm with an offset disk.

View larger version (15K): [in this window] [in a new window]   Fig. 3. Depth distribution of total organic C as affected by year, tillage, and cover crop management. Error bars denote significance (P = 0.05) among tillage and cover crop management variables within a depth and year of sampling.

View larger version (35K): [in this window] [in a new window]   Fig. 4. Relationship of the flush of CO2 following rewetting of dried soil to total soil organic C, total soil N, soil microbial biomass C, particulate organic C, and potential C and N mineralization; b0 = intercept, b1 = slope, and r2 = strength of relationship. Total number of observations is 646 for each variable.

View larger version (28K): [in this window] [in a new window]   Fig. 5. Total organic C in water-stable aggregate fractions on a whole-soil basis as affected by year of sampling, soil depth, and tillage management. Large macroaggregates are 1 to 4.75 mm, small macroaggregates are 0.25 to 1 mm, and microaggregates are 0.05 to 0.25 mm. * Significant at P 0.05. ** Significant at P 0.01. *** Significant at P 0.001.

View larger version (24K): [in this window] [in a new window]   Fig. 6. Temporal change in total soil organic C, total soil N, particulate organic C, soil microbial biomass C, and net N mineralization as affected by management system (conventional-tillage [CT], no-till [NT], and continuation of pasture) and soil depth (0–6, 0–12, and 0–20 cm). Differences in slopes are noted in each panel. * Significant at P 0.05. ** Significant at P 0.01. *** Significant at P 0.001. There were no significant differences between pasture and NT.