R/fW.Daycent1.R

In SoilR: Models of Soil Organic Matter Decomposition

#' Effects of moisture on decomposition rates according to the DAYCENT model
#' 
#' Calculates the effects of Soil Water Content on decomposition rates
#' according to the Daycent Model.
#' 
#' 
#' @param swc A scalar or vector with soil water content of a soil layer (cm).
#' @param a Empirical coefficient. For fine textured soils a = 0.6. For coarse
#' textured soils a = 0.55.
#' @param b Empirical coefficient. For fine textured soils b = 1.27. For coarse
#' textured soils b = 1.70.
#' @param c Empirical coefficient. For fine textured soils c = 0.0012. For
#' coarse textured soils c = -0.007.
#' @param d Empirical coefficient. For fine textured soils d = 2.84. For coarse
#' textured soils d = 3.22.
#' @param partd Particle density of soil layer.
#' @param bulkd Bulk density of soil layer (g/cm^3).
#' @param width Thickness of a soil layer (cm).
#' @return A data frame with values of water filled pore space (wfps) and
#' effects of soil water content on decomposition rates. Both vectors are
#' unitless.
#' @references Kelly, R. H., W. J. Parton, M. D. Hartman, L. K. Stretch, D. S.
#' Ojima, and D. S. Schimel (2000), Intra-annual and interannual variability of
#' ecosystem processes in shortgrass steppe, J. Geophys. Res., 105.
fW.Daycent1= structure(
  function 
  (swc,         
   a=0.6,       
   b=1.27,      
   c=0.0012,    
   d=2.84,      
   partd=2.65,  
   bulkd=1,     
   width=1     
   )
  {
    porespace=1-(bulkd/partd)
    wfps=(swc/width)*(1/porespace)
    wfunc=(((wfps-b)/(a-b))^(d*((b-a)/(a-c))))*((wfps-c)/(a-c))^d
    return(data.frame(wfps,wfunc))
  }
  ,
  ex=function(){
     swc=seq(0,0.8,by=0.01)  
     fine=fW.Daycent1(swc)
     coarse=fW.Daycent1(swc,a=0.55,b=1.7,c=-0.007,d=3.22)
     plot(fine,type="l",xlim=c(0,1))
     lines(coarse,lwd=2)
     legend("topleft",c("coarse","fine"),lty=c(1,1),lwd=c(2,1),bty="n")
  }
)