Graaff, J. d. (1996). The price of soil erosion: An economic evaluation of soil conservation and watershed development. Wageningen Agricultural University.
توثيق أسلوب شيكاغو (الطبعة السابعة عشر)Graaff, J. de. The Price of Soil Erosion: An Economic Evaluation of Soil Conservation and Watershed Development. Wageningen, Netherlands: Wageningen Agricultural University, 1996.
توثيق جمعية اللغة المعاصرة MLA (الطبعة الثامنة)Graaff, J. de. The Price of Soil Erosion: An Economic Evaluation of Soil Conservation and Watershed Development. Wageningen Agricultural University, 1996.
تحذير: قد لا تكون هذه الاستشهادات دائما دقيقة بنسبة 100%.