HR: 0800h
AN: B11A-1023    [Abstracts]
TI: Effects of Tillage on Soil C Flux and Microbial Ecology Following Additions of ¹³C- and ¹⁵N-Labeled Grain Sorghum
AU: * White, P M
EM: pmwhite@ksu.edu
AF: Kansas State University Department of Agronomy, 2004A Throckmorton Plant Sciences Center, Manhattan, KS 66506 United States
AU: Rice, C W
EM: cwrice@ksu.edu
AF: Kansas State University Department of Agronomy, 2004A Throckmorton Plant Sciences Center, Manhattan, KS 66506 United States
AB: Soil management has been shown to change soil C levels, possibly due to changes in kinetics or processing of organic C. A proposed mechanism of increased C in no-tillage agricultural systems is the formation of larger size classes of soil aggregates. Simultaneous measurements of soil microbial ecology along with C dynamics provide insights into the microbial community responsible for larger aggregation formation and C accrual in soil. The objective of this field experiment was to monitor the ¹³C and ¹⁵N levels in soil and aggregates and the soil microbial ecology during the decomposition of applied ¹³C- and ¹⁵N-grain sorghum (Sorghum bicolor) residue. The labeled sorghum residue was obtained by pulse labeling 100 atom% ¹³CO₂ and fertilizing with 10 atom% (¹⁵NH₄)₂SO₄ growth chamber grown plants. Residue was harvested and applied to the top 15 cm or the soil surface of PVC microcosms for l (T) or no-tillage (NT), respectively. Microcosms were destructively sampled at 0, 3, 16, 25, 40, 68, and 159 d for measurement of total soil ¹³C and ¹⁵N in the whole soil and that contained in > 1000, 250-1000, 53-250, and 20-53 mm aggregate size fractions. Soil microbial phospholipids and neutral lipids were also evaluated. Total soil C values were not altered by the addition of plant residue, with values of 30, 30, 38, and 28 Mg C/ha for CT 0-5 cm, CT 5-15 cm, NT 0-5 cm, and NT 5-15 cm, respectively. Kinetics of residue decomposition were not different between tillage systems in the decomposition of added ¹³C with values for rapid and slow rates of 0.0316 and 0.0024/day, respectively. Data relating to soil aggregate ¹³C and ¹⁵N and microbial ecology will be presented at the meeting.
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
SC: Biogeosciences [B]
MN: Fall Meeting 2005