Growth of Rudbeckia and Leaching of Nitrates in Potting Media Amended with Composted Coffee Processing Residue,Municipal Solid Waste and Sewage Sludge

Composts made from coffee processing residue (CFPR), source separated municipal solid waste (MSW), sewage sludge and wood chips (SSWC), and sewage sludge, wood ash, wood chips and leaves (SSACL) were examined as replacements for the peat, perlite and sand found in a conventional potting medium. The perennial flower Rudbeckia hirta L. ‘Goldilocks’ (Black-Eyed Susan) was grown in media composed of 0, 10, 25, 50, 80, and 100 (percent by vol) of each compost. Leachate from media containing 0, 25, 50, and 100% compost was tested for NO₃-N and NH₃-N + NH₄-N to determine if compost would increase the potential for potting media to be a source of nitrate in surface and ground water. The effects of two mid season applications of liquid fertilizer on plant growth and nitrogen leaching were also examined.

Compared to a conventional medium without compost, differences in the growth of Rudbeckia in media with compost were few. Statistically significant decreases in growth occurred in media containing 80 and 100% CFPR, and 80% SSACL. None of the composts caused a statistically significant increase in growth. Leaching of nitrogen increased from media containing 100% CFPR, SSWC and SSACL compared to the medium with no compost. Media containing 25, 50, and 100% MSW leached less N the conventional medium. Liquid fertilizer did not significantly change the growth of Rudbeckia or the amount of nitrogen found in the leachate from any medium.