gomez.seedrate {agridat} | R Documentation

## Rice yield at six different densities

### Description

Rice yield at six different densities

### Format

A data frame with 24 observations on the following 3 variables.

`rate`

  kg seeds per hectare

`rep`

  rep (block), four levels

`yield`

  yield, kg/ha

### Details

Rice yield at six different densities in an RCB design.

### Source

Gomez, K.A. and Gomez, A.A. 1984, Statistical Procedures for Agricultural Research. Wiley-Interscience. Page 26.

Used with permission of Kwanchai Gomez.

### Examples

    data(gomez.seedrate)
    dat <- gomez.seedrate

    require(lattice)
    xyplot(yield ~ rate, data=dat, group=rep, type='b',
           main="gomez.seedrate", auto.key=list(columns=4))

    # Quadratic response.  Use raw polynomials so we can compute optimum
    m1 <- lm(yield ~ rep + poly(rate,2,raw=TRUE), dat)
    -coef(m1)[5]/(2*coef(m1)[6]) # Optimum is at 29

    # Plot the model predictions
    if(require(latticeExtra)){
    newdat <- expand.grid(rep=levels(dat$rep), rate=seq(25,150))
    newdat$pred <- predict(m1, newdat)
    p1 <- aggregate(pred ~ rate, newdat, mean) # average reps
      xyplot(yield ~ rate, data=dat, group=rep, type='b',
             main="gomez.seedrate (with model predictions)", auto.key=list(columns=4)) +
        xyplot(pred ~ rate, p1, type='l', col='black', lwd=2)
    }

[Package agridat version 1.16 Index]