Παραπομπή σε μορφή APA (7η εκδ.)

Graaff, J. d. (1996). The price of soil erosion: An economic evaluation of soil conservation and watershed development. Wageningen Agricultural University.

Παραπομπή σε μορφή Chicago (17η εκδ.)

Graaff, J. de. The Price of Soil Erosion: An Economic Evaluation of Soil Conservation and Watershed Development. Wageningen, Netherlands: Wageningen Agricultural University, 1996.

Παραπομπή σε μορφή MLA (8th εκδ.)

Graaff, J. de. The Price of Soil Erosion: An Economic Evaluation of Soil Conservation and Watershed Development. Wageningen Agricultural University, 1996.