Soil production function refers to the rate of

bedrock In geology, bedrock is solid Rock (geology), rock that lies under loose material (regolith) within the crust (geology), crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface mater ...

weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement), ...

into

soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...

as a function of soil thickness. A general model suggested that the rate of physical

of bedrock (de/dt) can be represented as an exponential decline with soil thickness:

de/dt = P_0 \exp

where ''h'' is soil thickness ''P₀'' m/yearis the potential (or maximum) weathering rate of bedrock and ''k'' ⁻¹is an empirical constant. The reduction of weathering rate with thickening of soil is related to the exponential decrease of

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

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 Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologic ...

and type of parent materials. found the value of ''P₀'' ranges from 0.08 to 2.0 mm/yr for sites in

Northern California Northern California (colloquially known as NorCal) is a geographic and cultural region that generally comprises the northern portion of the U.S. state of California. Spanning the state's northernmost 48 counties, its main population centers incl ...

, and 0.05–0.14 mm/yr for sites in Southeastern

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

. Meanwhile values of ''k'' do not vary significantly, ranging from 2 to 4 m⁻¹. A number of

landscape evolution model A landscape evolution model is a physically-based numerical model that simulates changing terrain over the course of time. The change in, or evolution of, terrain, can be due to: glacial or fluvial erosion, sediment transport and deposition, regol ...

s have adopted the so-called ''humped'' model.The humped soil production function
Arjun Heimsath. Arizona State University, Earth and Space Exploration This model dates back to G.K. Gilbert's ''Report on the Geology of the Henry Mountains'' (1877). Gilbert reasoned that the

of bedrock was fastest under an intermediate thickness of soil and slower under exposed bedrock or under thick mantled soil. This is because chemical

requires the presence of water. Under thin soil or exposed bedrock water tends to run off, reducing the chance of the decomposition of bedrock.

References

Bibliography

* * * * * {{soil science topics Mathematical modeling Pedology

See also

References

Bibliography