Gaya APA

MacCarthy, P. et al (1990). Humic Substances in Soil and Crop Sciences : Selected Readings . USA: American Society of Argonomy, Inc.

Gaya MLA

MacCarthy, P.. et al. "Humic Substances in Soil and Crop Sciences : Selected Readings". USA: American Society of Argonomy, Inc, 1990. Text.