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[[Image:Prod_fun.jpg|right|thumb|300px|Soil production function]]
'''Soil production function''' refers to the rate of [[bedrock]] [[weathering]] into [[soil]] as a function of soil thickness.

A general model suggested that the rate of physical [[weathering]] of bedrock (de/dt) can be represented as an exponential decline with soil thickness:

<math> de/dt = P_0 \exp{[-k h]}\ </math>

where ''h'' is soil thickness [m], ''P0'' [mm/year] is the potential (or maximum) weathering rate of bedrock and ''k'' [m−1] is an empirical constant.

The reduction of weathering rate with thickening of soil is related to the exponential decrease of [[temperature]] amplitude with increasing depth below the soil surface, and also the exponential decrease in average water penetration (for freely-drained soils). Parameters ''P0'' and ''k'' are related to the [[climate]] and type of parent materials. {{Harvtxt|Heimsath|Dietrich|Nishiizumi|Finkel|1997}} found the value of ''P0'' ranges from 0.08 to 2.0 mm/yr for sites in [[Northern California]], and 0.05–0.14 mm/yr for sites in Southeastern [[Australia]]. Meanwhile values of ''k'' do not vary significantly, ranging from 2 to 4 m−1.

A number of [[landscape evolution model]]s have adopted the so-called ''humped'' model. This model dates back to [[Grove Karl Gilbert|G.K. Gilbert's]] ''Report on the Geology of the Henry Mountains'' (1877). Gilbert reasoned that the [[weathering]] of bedrock was fastest under an intermediate thickness of soil and slower under exposed bedrock or under thick mantled soil. This is because chemical [[weathering]] requires the presence of water. Under thin soil or exposed bedrock water tends to run off, reducing the chance of the decomposition of bedrock.

==See also==
*[[Biorhexistasy]]
*[[Parent material]]
*[[Pedogenesis]]
*[[Weathering]]

==References==
*{{cite journal |last=Ahnert |first=F. |year=1977 |title=Some comments on the quantitative formulation of geomorphological process in a theoretical model |journal=Earth Surface Processes |volume=2 |issue= |pages=191–201 |doi= }}
*{{cite journal |last=Heimsath |first=A. M. |last2=Dietrich |first2=W. E. |last3=Nishiizumi |first3=K. |last4=Finkel |first4=R. C. |year=1997 |title=The soil production function and landscape equilibrium |journal=[[Nature (journal)|Nature]] |volume=388 |issue=6640 |pages=358–361 |doi=10.1038/41056 |ref=harv }}
*{{cite journal |last=Humphreys |first=G. S. |last2=Wilkinson |first2=M. T. |year=2007 |title=The soil production function: a brief history and its rediscovery |journal=Geoderma |volume=139 |issue= |pages=73–78 |doi= |url=http://www.uky.edu/AS/Geography/People/Faculty/Wilkinson/HumphreysWilkinson2007HistorySPF.pdf }}
*{{cite journal |last=Wilkinson |first=M. T. |last2=Chappell |first2=J. |last3=Humphreys |first3=G. S. |last4=Fifield |first4=K. |last5=Smith |first5=B. |last6=Hesse |first6=P. P. |year=2005 |title=Soil production in heath and forest, Blue Mountains, Australia: influence of lithology and palaeoclimate |journal=Earth Surface Processes and Landforms |volume=30 |issue= |pages=923–934 |url=http://www.uky.edu/AS/Geography/People/Faculty/Wilkinson/2005-WilkinsonSoilprodnBlueMtns.pdf }}
*{{cite journal |last=Wilkinson |first=M. T. |last2=Humphreys |first2=G. S. |year=2005 |title=Exploring pedogenesis via nuclide-based soil production rates and OSL-based bioturbation rates |journal=Australian Journal of Soil Research |volume=43 |issue= |pages=767–779 |doi= 10.1071/SR04158|url=http://www.uky.edu/AS/Geography/People/Faculty/Wilkinson/2005-WilkinsonHumphreysPedogenesisAJSR.pdf }}

[[Category:Pedology]]

Kinetic resolution - Revision history

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