When citing cdlTools, please cite both the package and underlying data sources used:

Chen L, Lisic J (2018). Tools to Download and Work with USDA Cropscape Data. https://cran.r-project.org/package=cdlTools.

USDA-NASS (2019). National Agricultural Statistics Service Cropland Data Layer. https://nassgeodata.gmu.edu/CropScape/.

Corresponding BibTeX entries:

  @Manual{,
    author = {Lu Chen and Jonathan Lisic},
    title = {Tools to Download and Work with USDA Cropscape Data},
    year = {2018},
    url = {https://cran.r-project.org/package=cdlTools},
  }

  @Manual{,
    author = {{USDA-NASS}},
    title = {National Agricultural Statistics Service Cropland Data
      Layer},
    year = {2019},
    url = {https://nassgeodata.gmu.edu/CropScape/},
  }