Soil Organic Carbon Accretion vs. Sequestration Using Physicochemical Fractionation and CQESTR Simulation

Accurate estimates of soil organic C (SOC) stocks are required to determine changes in SOC resulting from agricultural management practices. Our objectives were to: (i) determine total SOC; (ii) estimate the contribution of light fraction C (LF-C) to total SOC; and (iii) simulate SOC dynamics using...

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Bibliographic Details
Published in:Soil Science Society of America journal 2013-03, Vol.77 (2), p.618-629
Main Authors: Gollany, H. T, Fortuna, A. M, Samuel, M. K, Young, F. L, Pan, W. L, Pecharko, M
Format: Article
Language:English
Subjects:
carbon sequestration
Climate change
crop residues
crop rotation
fallow
Fractionation
Fractions
Hordeum vulgare
no-tillage
physicochemical properties
Precipitation
Simulation
simulation models
soil depth
soil nutrient dynamics
soil organic carbon
soil sampling
Soil sciences
spring
spring barley
spring wheat
Tillage
Triticum aestivum
winter wheat
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Summary:Accurate estimates of soil organic C (SOC) stocks are required to determine changes in SOC resulting from agricultural management practices. Our objectives were to: (i) determine total SOC; (ii) estimate the contribution of light fraction C (LF-C) to total SOC; and (iii) simulate SOC dynamics using CQESTR to examine the effect of climate change for three cropping systems in the Pacific Northwest. The LF-C masked small gains or losses in measured SOC for all cropping systems. Simulated data indicated no significant changes in SOC in the top 30 cm of the sweep-tillage winter wheat (Triticum aestivum L.)-tillage fallow rotation (WW-TF) and no-till (NT) spring wheat-chemical fallow rotation (SW-CF/NT), whereas SOC increased in the NT spring barley (Hordeum vulgare L.)-spring wheat rotation (SB-SW/NT). The apparent increase in measured SOC with continuous NT spring cropping was the result of accumulated undecomposed crop residues that contributed to the labile C pool and was confirmed via LF-C analysis. The contributions of the LF-C to total SOC across cropping systems ranged from 13.4 to 18.4% (fall soil samples) and 14.4 to 18.9% (spring soil samples). Modeling predicted no significant change in SOC stocks for the WW-TF and SW-CF/NT rotations, even with a 30% crop biomass increase based on potential climate change scenarios. Differences between the observed and predicted SOC were due to artifacts associated with protocols used to determine SOC that did not completely remove accrued crop residue and could be explained by LF-C, which provided a first approximation of organic C accretion.
ISSN:0361-5995
1435-0661
DOI:10.2136/sssaj2012.0303