ivins.herbs {agridat} | R Documentation

## Percent ground cover of herbage species and nettles.

### Description

Percent ground cover of herbage species and nettles.

### Format

A data frame with 78 observations on the following 4 variables.

`block`

  block, 6 levels

`gen`

  genotype, 13 levels

`nettle`

  percent ground cover of nettles

`herb`

  percent ground cover of herbage species

### Details

On the University of Nottingham farm, 13 different strains and species of herbage plants were sown on about 4 acres in an RCB design. Each grass species was sown together with white clover seed.

During establishment of the herbage plants, it became apparent that Urtica dioica (nettle) became established according to the particular herbage plant in each plot. In particular, nettle became established in plots sown with leguminous species and the two grass species. The graminaceous plots had less nettles.

The data here are the percentage ground cover of nettle and herbage plants in September 1951.

Note, some of the percent ground cover amounts were originally reported as 'trace'. These have been arbitrarily set to 0.1 in this data.

gen | species | strain
G01 | Lolium perenne | Irish perennial ryegrass
G02 | Lolium perenne | S. 23 perennial ryegrass
G03 | Dactylis glomerata | Danish cocksfoot
G04 | Dactylis glomerata | S. 143 cocksfoot
G05 | Phleum pratense | American timothy
G06 | Phleum pratense | S. 48 timothy
G07 | Festuca pratensis | S. 215 meadow fescue
G08 | Poa trivialis | Danish rough stalked meadow grass
G09 | Cynosurus cristatus | New Zealand crested dogstail
G10 | Trifolium pratense | Montgomery late red clover
G11 | Medicago lupulina | Commercial black medick
G12 | Trifolium repens | S. 100 white clover
G13 | Plantago lanceolata | Commercial ribwort plantain

### Source

Ivins, JD. (1952). Concerning the Ecology of Urtica Dioica L., Journal of Ecology, 40, 380-382. http://doi.org/10.2307/2256806

### References

Ivins, JD (1950). Weeds in relation to the establishment of the Ley. Grass and Forage Science, 5, 237–242. http://doi.org/10.1111/j.1365-2494.1950.tb01287.x

O'Gorman, T.W. (2001). A comparison of the F-test, Friedman's test, and several aligned rank tests for the analysis of randomized complete blocks. Journal of agricultural, biological, and environmental statistics, 6, 367–378. http://doi.org/10.1198/108571101317096578

### Examples

    data(ivins.herbs)
    dat <- ivins.herbs

    # Nettle is primarily established in legumes.
    require(lattice)
    xyplot(herb~nettle|gen, dat, main="ivins.herbs - herb yield vs weeds",
           xlab="Percent groundcover in nettles",
           ylab="Percent groundcover in herbs")

    # O'Brien used first 7 species to test gen differences
    dat7 <- droplevels(subset(dat, is.element(gen, c('G01','G02','G03','G04','G05','G06','G07'))))
    m1 <- lm(herb ~ gen + block, data=dat7)
    anova(m1) # gen p-value is .041
    ## Response: herb
    ##           Df  Sum Sq Mean Sq F value  Pr(>F)
    ## gen        6 1083.24 180.540  2.5518 0.04072 *
    ## block      5  590.69 118.138  1.6698 0.17236
    ## Residuals 30 2122.48  70.749

    friedman.test(herb ~ gen|block, dat7) # gen p-value .056

[Package agridat version 1.16 Index]