Coffee pulp compost: Chemical properties and distribution of humic substances


Coffee pulp
Humid acid

How to Cite

Chong, J. A., & Dumas, J. A. (2012). Coffee pulp compost: Chemical properties and distribution of humic substances. The Journal of Agriculture of the University of Puerto Rico, 96(1-2).


The distribution and chemical properties of humic substances (humic acids and fulvic acids) from a twelve-month-old static aerated compost pile of coffee pulp were studied. The compost was separated into five physical granule fractions (500, 1000, 2000, 4000 and 8000 um) in order to determine the effect of particle size on humic substances, on nutrient composition, and on distribution. The objective of this study was to understand the chemical properties and distribution of humic substances in mature coffee pulp compost. There were no significant differences across fractions for total N and available P2O5; these fractions averaged 4.9 and 0.66%, respectively. Potassium (K) increased as fraction size increased, from 3.01 to 3.94%. Readily available nitrogen, NO3 and NH4, was 7.19% of the total N. Eighty-nine percent of the total K was exchangeable K ions, and these varied within compost fractions from 2.82 to 3.33%. Approximately 50% of the total Ca and Mg were exchangeable ions; Ca ions varied from 2.13 to 3.01%, and Mg ions varied from 0.22 to 0.26% among fractions. Sequential extraction of organic carbon showed higher extractable carbon by the extraction with 0.1 N NaOH for 24 h, followed by 0.1 N NaOH for 2 h, and water for 2 h. The optical densities E4/E6 ratio ranged between 6.6 and 8.5 for humic acids (HA) extracted with NaOH for 2 h. The diversity in humic substances (HS) and exchangeable ions among compost fractions indicates that nutrient release is regulated by the size of the granules. In conclusion, these data demonstrate that smaller size particles have greater humification rates, and that N and available P are similar across particle sizes, thus providing an excellent soil compost amendment.


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