my.datafile <- tempfile()
cat(file=my.datafile, " 
1 1 A 31.0 
1 2 B 39.5 
1 3 C 30.5 
2 1 B 34.0 
2 2 C 24.5 
2 3 A 28.0 
3 1 C 15.0 
3 2 A 25.5 
3 3 B 31.0
", sep=" ")

options(scipen=999) # suppressing scientific notation

fielddata <- read.table(my.datafile, header=FALSE, col.names=c("orientation", "location", "variety", "yield")) 

attach(fielddata)

orientation <- factor(orientation)

location <- factor(location)

variety <- factor(variety)