R/fW.Century.R

In SoilR: Models of Soil Organic Matter Decomposition

#' Effects of moisture on decomposition rates according to the CENTURY model
#' 
#' Calculates the effects of precipitation and potential evapotranspiration on
#' decomposition rates.
#' 
#' 
#' @param PPT A scalar or vector containing values of monthly precipitation.
#' @param PET A scalar or vector containing values of potential
#' evapotranspiration.
#' @return A scalar or a vector containing the effects of precipitation and
#' potential evapotranspiration on decomposition rates (unitless).
#' @references Adair, E. C., W. J. Parton, S. J. D. Grosso, W. L. Silver, M. E.
#' Harmon, S. A. Hall, I. C. Burke, and S. C. Hart (2008), Simple three-pool
#' model accurately describes patterns of long-term litter decomposition in
#' diverse climates, Global Change Biology, 14(11), 2636-2660.  Parton,
#' W. J., J. A. Morgan, R. H. Kelly, and D. S. Ojima (2001), Modeling soil C
#' responses to environmental change in grassland systems, in The potential of
#' U.S. grazing lands to sequester carbon and mitigate the greenhouse effect,
#' edited by R. F. Follett, J. M. Kimble and R. Lal, pp. 371-398, Lewis
#' Publishers, Boca Raton.
fW.Century<- structure(
  function 
     (PPT,     
     PET   
     )
   {
      1/(1+30*exp(-8.5*(PPT/PET)))
   }
    ,
    ex=function(){
      PPT=seq(0,1500,by=10)
      PET=rep(1500,length(PPT))
      PPT.PET=fW.Century(PPT,PET)
      plot(PPT/PET,PPT.PET, 
           ylab="f(PPT, PET) (unitless)", 
           main="Effects of precipitation and potential evapotranspiration on decomposition rates")
    }
)