To cite package 'spgrass6' in publications use your choice of:

Roger Bivand (2014). spgrass6: Interface between GRASS 6 and R. R package version 0.8-6.

Roger Bivand (2007). Using the {R}--{GRASS} Interface: Current Status. OSGeo Journal, 1, pp. 36-38

Roger S. Bivand, Edzer J. Pebesma and Virgilio Gomez-Rubio (2008) Applied Spatial Data Analysis with R. Springer, New York.

Markus Neteler and Helena Mitasova (2008) Open Source GIS: a GRASS GIS Approach. Springer, New York.

Corresponding BibTeX entries:

  @Manual{,
    title = {{spgrass6}: Interface between GRASS 6 and R},
    author = {Roger Bivand},
    year = {2014},
    note = {R package version 0.8-6},
    url = {http://CRAN.R-project.org/package=spgrass6},
  }
  @Article{,
    title = {Using the {R}--{GRASS} Interface: Current Status},
    author = {Roger Bivand},
    year = {2007},
    journal = {{OSGeo} Journal},
    volume = {1},
    pages = {36--38},
    url =
      {http://www.osgeo.org/files/journal/final_pdfs/OSGeo_vol1_GRASS-R.pdf},
  }
  @Book{,
    title = {Applied Spatial Data Analysis with {R}},
    author = {Roger S. Bivand and Edzer J. Pebesma and Virgilio
      Gomez-Rubio},
    year = {2008},
    publisher = {Springer},
    address = {New York},
  }
  @Book{,
    title = {Open Source {GIS}: a {GRASS} {GIS} Approach},
    author = {Markus Neteler and Helena Mitasova},
    year = {2008},
    publisher = {Springer},
    address = {New York},
  }