Spatial Analysis of Multienvironment trials

Generating/Checking spatial coding

Consider the simultaneous analysis of a series of trials with similar treatments and layout. For field trials, the residuals are independent between trials but may be spatially within trials. At the treatment level there is the average effect of treatments across trials and the interaction of treatment with trial. For analysis in ASReml, the data for each trial needs to be arranged conformably in a single or multiple files, sorted by trial. The data also needs to be sorted into plot order but this can be done by ASReml if the rows and columns are coded in the data file. Assume we have a data field site which identifies the trial, and fields row and column which code for the spatial arrangement within trials.

Syntax

When !SECTION site !ROWFAC row !COLFAC column
is specified, ASReml generates the R-structure lines to fit a separable first-order autoregressive ( AR1 x AR1 ) variance structure for each site.

     column is the name of a factor or variate containing column numbers (1 ... nc where nc is the number of columns) on which the data is to be sorted.
     row is the name of a factor or variate containing row numbers (1 ... nr where nr is the number of rows) on which the data is to be sorted.
     site is the name of a factor or variate containing site numbers (1 ... ns where ns is the number of sites) on which the data is already sorted.

When !SECTION site is specified ASReml will check that sections have been correctly dimensioned but assumes the data records are presorted with respect to site. When !ROWFAC row and !COLFAC column are also specified, ASReml will construct the R-structure lines required to model the spatial variance as AR1 x AR1 with initial correlation parameters of 0.1, such that the data is sorted into plot order: columns within rows within sites. The R structure lines that a user would normally be required to work out and type into the .as file are written to the .res file. The user may then cut and paste them into the .as file for a later run if the structures need to be modified.

The number of rows and columns within a trial does not have to be the same across trials.

Example

The following is a basic example assuming 5 sites (sections).

 Syntax Basic multi-environment trial analysis
  site   5        # sites coded 1 ... 5
  column *        # columns coded 1 ...
  row    *        # rows coded 1 ...
  variety !A      # variety  names
  yield
 met.dat !SECTION site !ROWFAC row !COLFAC col
 yield ~ site !r variety site.variety !f mv
 site 2 0         # variance header line
                  # asreml inserts the 10 lines required to
                  # define the R structure lines for the five sites

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