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SOIL BIOLOGY & BIOCHEMISTRY

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

^* Corresponding author (alan.franzluebbers{at}ars.usda.gov).

Tillage, cropping system, and cover cropping are important management variables that control the quantity, quality, and placement of organic matter inputs to soil. How soil organic matter and its different fractions respond to management has not been comprehensively studied in integrated crop–livestock systems. We conducted a 3-yr field experiment on a Typic Kanhapludult in Georgia in which long-term pasture was terminated and converted to annual crops. Tillage systems were conventional (CT, moldboard plowed initially and disked thereafter) and no-till (NT). Cropping systems were summer grain with winter cover crop and winter grain with summer cover crop. Cover crops were either grazed by cattle or left unharvested. Total organic C was highly stratified with depth under NT and relatively uniformly distributed with depth under CT. All soil C and N fractions were greater under NT than under CT at a depth of 0 to 6 cm. Tillage system had the most dominant influence on all soil C and N fractions, and cropping system the least. At the end of 3 yr, total organic C at a depth of 0 to 30 cm was lower under CT than under NT (42.6 vs. 47.4 Mg ha^–1 [P < 0.001]). Potential C mineralization was also lower under CT than under NT (1240 vs. 1371 kg ha^–1 during 24 d [P = 0.02]). At a depth of 0 to 30 cm, cover crop management had no effect on soil C and N fractions, but within the surface 6 cm some changes occurred with grazing of cover crops by cattle, the most dramatic of which were 1 ± 9% increase in soil microbial biomass C and 3 ± 16% decrease in potential C mineralization. To preserve high surface-soil C and N fractions and total plow-layer contents, NT cropping following termination of perennial pasture is recommended. In addition, since cattle grazing cover crops did not consistently negatively influence soil C and N fractions, integrated crop–livestock systems are recommended as a viable conservation approach while intensifying agricultural land use.

Abbreviations: CT, conventional tillage • NT, no-till