To cite ade4 in publications use:

Dray S, Dufour A (2007). “The ade4 Package: Implementing the Duality Diagram for Ecologists.” Journal of Statistical Software, 22(4), 1–20. doi:10.18637/jss.v022.i04.

Bougeard S, Dray S (2018). “Supervised Multiblock Analysis in R with the ade4 Package.” Journal of Statistical Software, 86(1), 1–17. doi:10.18637/jss.v086.i01.

Chessel D, Dufour A, Thioulouse J (2004). “The ade4 Package – I: One-Table Methods.” R News, 4(1), 5–10. https://cran.r-project.org/doc/Rnews/.

Dray S, Dufour A, Chessel D (2007). “The ade4 Package – II: Two-Table and K-Table Methods.” R News, 7(2), 47–52. https://cran.r-project.org/doc/Rnews/.

Thioulouse J, Dray S, Dufour A, Siberchicot A, Jombart T, Pavoine S (2018). Multivariate Analysis of Ecological Data with ade4. Springer. doi:10.1007/978-1-4939-8850-1.

Corresponding BibTeX entries:

  @Article{,
    title = {The {ade4} Package: Implementing the Duality Diagram for
      Ecologists},
    author = {St\'ephane Dray and Anne--B\'eatrice Dufour},
    journal = {Journal of Statistical Software},
    year = {2007},
    volume = {22},
    number = {4},
    pages = {1--20},
    doi = {10.18637/jss.v022.i04},
  }

  @Article{,
    title = {Supervised Multiblock Analysis in {R} with the {ade4}
      Package},
    author = {St\'ephanie Bougeard and St\'ephane Dray},
    journal = {Journal of Statistical Software},
    year = {2018},
    volume = {86},
    number = {1},
    pages = {1--17},
    doi = {10.18637/jss.v086.i01},
  }

  @Article{,
    title = {The {ade4} Package -- {I}: One-Table Methods},
    author = {Daniel Chessel and Anne-B\'eatrice Dufour and Jean
      Thioulouse},
    journal = {R News},
    year = {2004},
    volume = {4},
    number = {1},
    pages = {5--10},
    url = {https://cran.r-project.org/doc/Rnews/},
  }

  @Article{,
    title = {The {ade4} Package -- {II}: Two-Table and {K}-Table
      Methods},
    author = {St\'ephane Dray and Anne-B\'eatrice Dufour and Daniel
      Chessel},
    journal = {R News},
    year = {2007},
    volume = {7},
    number = {2},
    pages = {47--52},
    url = {https://cran.r-project.org/doc/Rnews/},
  }

  @Book{,
    title = {Multivariate Analysis of Ecological Data with {ade4}},
    author = {Jean Thioulouse and St\'ephane Dray and Anne--B\'eatrice
      Dufour and Aur\'elie Siberchicot and Thibaut Jombart and Sandrine
      Pavoine},
    year = {2018},
    publisher = {Springer},
    doi = {10.1007/978-1-4939-8850-1},
  }