Johnson, Emanuel L.; Campbell, T. Austin; Foy, Charles D. (November 1997). "Effect of soil pH on mineral element concentrations of two erythroxylum species". Journal of Plant Nutrition. 20 (11): 1503–1515. doi:10.1080/01904169709365352.
Ferreira, Jorge F. S.; Smeda, Reid J.; Duke, Stephen O. (August 1997). "Control of Coca Plants (Erythroxylum coca and E. novogranatense) with Glyphosate". Weed Science. 45 (4): 551–556. doi:10.1017/S0043174500088809.
