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Title: SOIL CARBON DYNAMICS DURING A LONG-TERM INCUBATION STUDY INVOLVING 13C AND 14C MEASUREMENTS.

Author
item Follett, Ronald
item PAUL, ELDOR - NREL/CSU, FT. COLLINS, CO
item Pruessner, Elizabeth

Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2006
Publication Date: 3/1/2007
Citation: Follett, R.F., Paul, E.A., Pruessner, E.G. 2007. Soil carbon dynamics during a long-term incubation study involving 13c and 14c measurements. Soil Biology and Biochemistry. 172:189-208.

Interpretive Summary: The measurement of decreases in SOC and SMB-C during an 853d incubation without added substrate made it possible to determine rates of loss of both and the role of organisms as a source of mineralizable C. Measurement of the 13C of the evolved CO2 during incubation made it possible to determine whether evolved C was from more recent corn residues or from the soil derived from the original native grassland. Acid hydrolysis and carbon dating before and after the extended incubation characterized the more resistant SOC components. These results, thus allow insights into the contribution of biomass and changes in isotope ratios in soil that were not previously available in the scientific literature.

Technical Abstract: This study used soils collected from the Central Great Plains Research Center near Akron, Colorado and from the High Plains Agricultural Laboratory located 8.3 km north of Sidney, NE. The Akron site is on a Weld loam, a fine montmorillonitic, mesic, Aridic Paleustoll with <1% slope. Treatments were no-till small grain crop-fallow rotations with wheat (Triticum aestivum L.), no-till continuous corn (Zea mays L.), and no-till corn, fallow, wheat and no-till corn (CFWC) in a 4-year rotation. The Sidney site is on a Duroc loam, a fine silty, mixed mesic Pachic Haplustoll with <1% slope. The Sidney plots were broken from native sod in 1970 and planted to wheat-fallow. Three replications of no-till and plow tillage treatments and sod-plot treatment were sampled. Soils were collected to 10 cm depth at both sites. The measurement of decreases in SOC and SMB-C during an 853d incubation without added substrate made it possible to determine the rates of loss of both and the role of organisms as a source of mineralizable C. Measurement of the 13C in evolved CO2 during the incubation allowed us to determine whether evolved C came from the more recent corn residues or was soil derived from original native grassland SOC. Acid hydrolysis and carbon dating before and after the extended incubation characterized the more resistant SOC components. Incubation malfunction between days 500 to 550 resulted in a 3- to 6.5ºC temperature increased in which microorganism respiration rate increased ~50% and raised the question of whether temperature or biochemical recalcitrance of the SOC was limiting. These results allow insights into the contribution of biomass and changes in isotope ratios in soil not previously available in the scientific literature.