yield.saemix: Wheat yield in crops treated with fertiliser, in SAEM format

In saemix: Stochastic Approximation Expectation Maximization (SAEM) Algorithm

Wheat yield in crops treated with fertiliser, in SAEM format

Description

Theyield.saemix contains data from winter wheat experiments.

Usage

yield.saemix

Format

This data frame contains the following columns:

site

the site number

dose

dose of nitrogen fertiliser (kg/ha)

yield

grain yield (kg/ha)

soil.nitrogen

end-of-winter mineral soil nitrogen (NO3- plus NH4+) in the 0 to 90 cm layer was measured on each site/year (kg/ha)

Details

The data in the yield.saemix comes from 37 winter wheat experiments carried out between 1990 and 1996 on commercial farms near Paris, France. Each experiment was from a different site. Two soil types were represented, a loam soil and a chalky soil. Common winter wheat varieties were used. Each experiment consisted of five to eight different nitrogen fertiliser rates, for a total of 224 nitrogen treatments. Nitrogen fertilizer was applied in two applications during the growing season. For each nitrogen treatment, grain yield (adjusted to 150 g.kg-1 grain moisture content) was measured. In addition, end-of-winter mineral soil nitrogen (NO3- plus NH4+) in the 0 to 90 cm layer was measured on each site-year during February when the crops were tillering. Yield and end-of-winter mineral soil nitrogen measurements were in the ranges 3.44-11.54 t.ha-1 , and 40-180 kg.ha-1 respectively.

Source

Makowski, D., Wallach, D., and Meynard, J.-M (1999). Models of yield, grain protein, and residual mineral nitrogen responses to applied nitrogen for winter wheat. Agronomy Journal 91: 377-385.

Examples

data(yield.saemix)
saemix.data<-saemixData(name.data=yield.saemix,header=TRUE,name.group=c("site"),
      name.predictors=c("dose"),name.response=c("yield"),
      name.covariates=c("soil.nitrogen"),units=list(x="kg/ha",y="t/ha",covariates=c("kg/ha")))

#  Model: linear + plateau
yield.LP<-function(psi,id,xidep) {
  x<-xidep[,1]
  ymax<-psi[id,1]
  xmax<-psi[id,2]
  slope<-psi[id,3]
  f<-ymax+slope*(x-xmax)
  #'  cat(length(f),"  ",length(ymax),"\n")
  f[x>xmax]<-ymax[x>xmax]
  return(f)
}
saemix.model<-saemixModel(model=yield.LP,description="Linear plus plateau model",   
        psi0=matrix(c(8,100,0.2,0,0,0),ncol=3,byrow=TRUE,dimnames=list(NULL,   
            c("Ymax","Xmax","slope"))),covariate.model=matrix(c(0,0,0),ncol=3,byrow=TRUE), 
        transform.par=c(0,0,0),covariance.model=matrix(c(1,0,0,0,1,0,0,0,1),ncol=3, 
            byrow=TRUE),error.model="constant")

saemix.options<-list(algorithms=c(1,1,1),nb.chains=1,seed=666, 
       save=FALSE,save.graphs=FALSE,displayProgress=FALSE)

# Plotting the data
plot(saemix.data,xlab="Fertiliser dose (kg/ha)", ylab="Wheat yield (t/ha)")


saemix.fit<-saemix(saemix.model,saemix.data,saemix.options)

# Comparing the likelihoods obtained by linearisation and importance sampling 
# to the likelihood obtained by Gaussian Quadrature
saemix.fit<-llgq.saemix(saemix.fit)
{
   cat("LL by Importance sampling, LL_IS=",saemix.fit["results"]["ll.is"],"\n")
   cat("LL by linearisation, LL_lin=",saemix.fit["results"]["ll.lin"],"\n")
   cat("LL by Gaussian Quadrature, LL_GQ=",saemix.fit["results"]["ll.gq"],"\n")
}

# Testing for an effect of covariate soil.nitrogen on Xmax
saemix.model2<-saemixModel(model=yield.LP,description="Linear plus plateau model", 
         psi0=matrix(c(8,100,0.2,0,0,0),ncol=3,byrow=TRUE,dimnames=list(NULL, 
            c("Ymax","Xmax","slope"))),covariate.model=matrix(c(0,1,0),ncol=3,byrow=TRUE), 
         transform.par=c(0,0,0),covariance.model=matrix(c(1,0,0,0,1,0,0,0,1),ncol=3, 
             byrow=TRUE),error.model="constant")

saemix.fit2<-saemix(saemix.model2,saemix.data,saemix.options)
# BIC for the two models
{
  cat("Model without covariate, BIC=",saemix.fit["results"]["bic.is"],"\n")
  cat("Model with covariate, BIC=",saemix.fit2["results"]["bic.is"],"\n")
  pval<-1-pchisq(-2*saemix.fit["results"]["ll.is"]+2*saemix.fit2["results"]["ll.is"],1)
  cat("        LRT: p=",pval,"\n")
}

#' @keywords datasets

saemix documentation built on May 29, 2024, 10:43 a.m.