Gan, Daqing, Shaban I. Kotob, and Daman S. Walia. “Evaluation of a Spectrophotometric Method for Practical and Cost Effective Quantification of Fulvic Acid”. Annals of Environmental Science 1 (March 7, 2007). Accessed May 3, 2024. https://openjournals.library.northeastern.edu/aes/journal/article/view/v1art2.