Soil

TOC

Description

Soils in LPJmL are represented as a set of soil layers, with distinct carbon and water pools. Litter pools can be situated above and below ground and areplant functional types](plant functional types)-specific. Litter pools are created with the establishment of PFTs.
Detailed description of new soil properties and the associated hydrology in Schaphoff et al., 2013[1].

Details

Each stand in each Grid_cells has a separate soil, i.e. it has it’s own [the soil water routine](water balance) and carbon pools. There are routines to consistently transfer water and carbon under land-use change, e.g. src/soil/copysoil.c and src/landuse/reclaim_land.c. Soil has 6 layers, of which 5 are hydrologically active (i.e. where soil water dynamcis are computed) and the BOTTOMLAYER is only a large heat capacity reservoir.
The evaporation layer depth is currently set to 300mm in src/soil/waterbalance.c but we also reduced that value to sometimes 10mm for some AgMIP sites to better match observations. A better relationship to soil texture and soil organic matter content (capilar rise) would be desirable.
See the soil water routine for details.
The description of carbon pools needs to be expanded, also for litter pools.

There is a distinction between LASTLAYER and BOTTOMLAYER for historic reasons, as these are different for the 2-layer and (new/standard) 6-layer implementation, see source:trunk/include/soil.h

Soil parameters are currently static over all soil layers and assigned via [soil code](soil codes) (classes), which is a static input, with pre-defined soil parameter. The current implementation has 12 different soil classes (and one void one) but in principle we can define as many soil classes as we want. In that case the code is prepared to read a soil class input file with a header, see src/soil/fopensoilcode.c Soil parameters are defined in source:trunk/par/soil_new.par

Technical Note

The so-called “new hydrology” is now standard in LPJmL4 and the only available option since the source code was cleaned on July 16, 2015. It was introduce for the Permafrost implementation by Sibyll et al.

soil parameters

Soil parameters are based on sand, silt and clay shares as provided by the HWSD. Shares have been averaged to aggregate from 5 arcmin to 0.5 degrees.
Based on these texture shares, soils have been classified following the USDA classification, leading to the 13 soil classes currently used in LPJmL. Hydraulic and thermal parameters have been derived for these soil classes, following Lawrence and Slater, as well as Cosby 1984.

Developer(s)

Sibyll Schaphoff and others.

See Also

parameter, the soil water routine, [plant functional types](plant functional types), litter, heat capacity

References

1. Schaphoff, S., Heyder, U., Ostberg, S., Gerten, D., Heinke, J., and Lucht, W.: Contribution of permafrost soils to the global carbon budget, Environmental Research Letters, 8, 014026, 10.1088/1748-9326/8/1/014026, 2013.

2. Lawrence, D.A. and A.G. Slater: Incorporating organic soil into a global climate model, Climate Dynamics, 30, 145-160, 2008