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ARS Home » Southeast Area » Tifton, Georgia » Southeast Watershed Research » Research » Publications at this Location » Publication #217523
Title: Tillage Effects on Microbial and Carbon Dynamics During Plant Residue Decomposition

Author
item White, Paul
item RICE, CHARLES - KANSAS STATE UNIV.

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/2/2008
Publication Date: 1/2/2009
Citation: White Jr, P.M., Rice, C.W. 2009. Tillage Effects on Microbial and Carbon Dynamics During Plant Residue Decomposition. Soil Science Society of America Journal. 73:138-145. doi:10.2136/ssaj2007.0384.

Interpretive Summary: One goal of soil carbon (C) sequestration, a greenhouse gas mitigation strategy, is to increase the mass of C stored in agricultural soils. Reducing soil disturbance, e.g. no-tillage, facilitates soil fungal growth and results in higher C sequestration rates. However, the specific mechanisms associated with short-term plant residue C and N retention are less clear. The objective of the experiment was to apply previously grown grain sorghum (Sorghum bicolor) residue to no-tillage and tillage soils, and measure the C and N retention, along with selected microbial parameters, during a growing season. The plant residue was decomposed rapidly regardless of tillage practice. Soil bacteria and fungal levels were higher in the NT surface layers during the most active period of plant residue decomposition. Smaller increases in microbial levels were observed in the CT plots. A significantly greater amount of C and N, derived from the plant residue, was present in the larger soil aggregate size fraction at the conclusion of the experiment. Data obtained indicate higher biological activity associated with NT soils, as compared to CT, and increased retention of plant residue C and N in macroaggregates, are two possible mechanisms for increased C and N retention in less disturbed agricultural systems.

Technical Abstract: One goal of soil carbon (C) sequestration, a greenhouse gas mitigation strategy, is to increase the mass of C stored in agricultural soils. Reducing soil disturbance, e.g. no-tillage, facilitates soil fungal growth and results in higher C sequestration rates. However, the specific mechanisms associated with short-term plant residue C and N retention are less clear. The objective of the experiment was to apply a 13C- and 15N-enriched grain sorghum (Sorghum bicolor) residue to no-tillage and tillage soils, and measure the 13C and 15N retention, along with soil microbial dynamics, during a growing season. The plant residue mineralized rapidly in both tillage systems, as indicated by 13C data. Mass balance calculations indicated that approximately 70% of the added 13C was mineralized to CO2 by 40 d. Total, Gm+ and Gm- bacteria, and fungal phospholipid fatty acids (PLFA) were higher in NT 0-5 cm during the most active period of residue mineralization as compared to the CT 0-5 or CT 5-15 cm depth. No changes were observed in the NT 5-15 cm depth. The >1000 'm aggregate size class retained the most 13C, regardless of tillage. The NT >1000 'm aggregates retained more 15N at the end of the experiment than other NT and CT aggregates size classes. Data obtained indicate higher biological activity associated with NT soils, as compared to CT, and increased retention of plant residue C and N in macroaggregates.