R/fW.Candy.R

In SoilR: Models of Soil Organic Matter Decomposition

#' Effects of moisture on decomposition rates according to the Candy model
#' 
#' Calculates the effects of water content and pore volume on decomposition
#' rates.
#' 
#' 
#' @param theta A scalar or vector containing values of volumetric soil water
#' content.
#' @param PV A scalar or vector containing values of pore volume.
#' @references J. Bauer, M. Herbst, J.A. Huisman, L. Weiherm\"uller, H.
#' Vereecken. 2008. Sensitivity of simulated soil heterotrophic respiration to
#' temperature and moisture reduction functions. Geoderma, Volume 145, Issues
#' 1-2, 15 May 2008, Pages 17-27.
fW.Candy<- structure(
  function 
  (theta,     
   PV   
  )
  {
    Mi=theta/PV 
    fw=ifelse(Mi<=0.5, 4*Mi*(1-Mi),1)
    return(fw)
  }
,
  ex=function(){
    th=seq(0,1,0.01)
    xi1=fW.Candy(theta=th,PV=0.4)
    xi2=fW.Candy(theta=th,PV=0.6)
    xi3=fW.Candy(theta=th,PV=0.8)
    plot(th,xi1,type="l",main="Effects of soil water content and pore volume on decomposition rates",
         xlab="Volumetric soil water content (cm3 cm-3)",ylab=expression(xi))
    lines(th,xi2,col=2)
    lines(th,xi3,col=3)
    legend("bottomright",c("Pore volume = 0.4","Pore volume = 0.6", "Pore volume = 0.8"),lty=1,col=1:3)
  }
)