1d:T78a,# Soil Pore Size Distribution The unimodal soil pore size distribution based on van Genuchten's model. ```r psd(thetaS, thetaR, alpha, n, h) ``` ## Arguments - `thetaS`: the water content at saturation. - `thetaR`: the residual water content. - `alpha`: the scale parameter of the van Genuchten's model (hPa-1). - `n`: the shape parameter in van Genuchten's formula. - `h`: a vector of water tension (hPa) on the range of water retention curve. ## Returns A numeric vector containing the soil pore size distribution as a function of soil water tension. ## Author(s) Renato Paiva de Lima ## References Ghiberto, P. J., Imhoff, S., Libardi, P. L., Silva, A. P. D., Tormena, C. A., Pilatti, M. A. (2015). Soil physical quality of Mollisols quantified by a global index. **Scientia Agricola**, 72(2):167-174. Asgarzadeh, H., Mosaddeghi, M. R., Nikbakht, A. M. (2014). SAWCal: A user-friendly program for calculating soil available water quantities and physical quality indices. **Computers and Electronics in Agriculture**, 109:86-93. ## Examples ```r # EXAMPLE 1 x <- seq(log10(1),log10(15000),len=100) h <- 10^x y <- psd(thetaR = 0.15,thetaS = 0.55, alpha = 0.048, n = 1.5, h=h) plot(x=h,y=y, log="x", xlab="h (hPa)", ylab=expression(delta*theta/delta*h), ylim=c(0,0.005)) # EXAMPLE 2 x <- seq(log10(1),log10(15000),len=100) h <- 10^x y <- psd(thetaR = 0.20,thetaS = 0.61, alpha = 0.1232, n = 1.3380,h=h) plot(x=h,y=y, log="x", xlab="h (hPa)", ylab=expression(delta*theta/delta*h), ylim=c(0,0.01)) # EXAMPLE 3 x <- seq(log10(1),log10(15000),len=100) h <- 10^x y <- psd(thetaR = 0.154,thetaS = 0.600, alpha = 0.103, n = 2.365,h=h) plot(x=h,y=y, log="x", xlab="h (hPa)", ylab=expression(delta*theta/delta*h), ylim=c(0,0.03)) ax <- c(1,10,100,1000,10000) radius <- r(h=ax) axis(3,at=ax, labels=round(radius,2)) mtext("Equivalent pore radius"~(mu*m),3,line=2.5, cex=0.9) # End (not run) ```

psd function