TITLE:
Fractal Kinetics Parameters Regulating Carbon Decomposition Rate under Contrasting Soil Management Systems
AUTHORS:
Léon E. Parent
KEYWORDS:
Aggregation, Annual Cropping, Carbon Pools, Carbon Sequestration, Fallow, Fractal Coefficient, Pasture, Soil Quality
JOURNAL NAME:
Open Journal of Soil Science,
Vol.7 No.7,
July
7,
2017
ABSTRACT: Agricultural soils can sequester and release large amounts of carbon. Accessibility
of soil carbon to microbial attacks depends on biological, chemical,
and physical protection mechanisms such as organic matter composition and
particle size, soil aggregation, and chemical protection through the silt-clayorganic
matter complex. While soil and organic matter are fractal objects
controlling exposure of reactive surfaces to the environment, soil aggregation
and biomass production and quality are regulated by agricultural practices.
Organic matter decomposition in soil is generally described by the classical
first-order kinetics equations fitted to define distinct carbon pools. By comparison,
fractal kinetics assigns a coefficient to adjust time-dependent decomposition
rate of total soil carbon to protection mechanisms. Our objective
was to relate fractal parameters of organic matter decomposition to soil
management systems. Retrieving published data, the decomposition of organic
matter was modeled in a silt loam soil maintained under pasture, annual
cropping or bare fallow during 11 years. The classical first-order kinetics
model returned quadratic relationships indicating that reactive carbon
decreased with time. Fractal kinetics rectified the relationships successfully.
Initial decomposition rate (k 1 at t = 1) was 7 × 10-4 for pasture, 1 × 10-4 for
annual cropping, and 0.5 × 10-4 for bare-soil fallow. Fractal coefficients h
were 0.71, 0.45, and 0.25 for pasture, annual cropping and fallow, respectively.
Due to aggregation, physical protection against microbial attacks was highest
under pasture management, leading to higher carbon sequestration despite
higher biomass production and “priming” effects. Parameters k 1 and h proved
to be useful indicators for soil quality classification integrating the opposite
effects of labile carbon decomposition and carbon protection mechanisms that
regulate the decomposition rate of organic matter with time as driven by soil
management practices.