To cite package 'RSAGA' in publications use:

Brenning, A., 2008. Statistical geocomputing combining R and SAGA: The example of landslide susceptibility analysis with generalized additive models. In J. Boehner, T. Blaschke and L. Montanarella (eds.), SAGA - Seconds Out (= Hamburger Beitraege zur Physischen Geographie und Landschaftsoekologie, vol. 19), p. 23-32.

Corresponding BibTeX entry:

  @InCollection{,
    author = {Alexander Brenning},
    title = {Statistical geocomputing combining R and SAGA: The example
      of landslide susceptibility analysis with generalized additive
      models},
    booktitle = {SAGA -- Seconds Out (= Hamburger Beitraege zur
      Physischen Geographie und Landschaftsoekologie, vol. 19)},
    publisher = {J. Boehner, T. Blaschke, L. Montanarella},
    year = {2008},
    pages = {23--32},
  }