Impact of spent coffee grounds as organic amendment on soil fertility and lettuce growth in two Mediterranean agricultural soils

ABSTRACT

The use of spent coffee grounds (SCG) as organic amendment is a triple solution: a reuse of this bio-residue (6 millions of tons per year), an increase in soil organic carbon (SCG contain 82% of carbohydrates and 13% of proteins) and a decrease in CO₂ emissions into the atmosphere. Thus, we investigate the effect of SCG on soil and plants in an in vitro assay. The variables considered were SCG dose (2.5 and 10%), two agricultural soils (Calcisol and Luvisol), and four cultivation times (15, 30, 45 and 60 days). The chemical and physicochemical soil properties, SEM images and growth parameters were analyzed. The highest dose of SCG increased organic carbon, total N and available K and P by 286%, 188%, 45%, and 9%, respectively, while decreasing lettuce growth by 233% compared to control. The SEM study revealed that SCG particles are incorporated into soil aggregates and microorganisms grow over them, which is also corroborated by a 10-times increase of soil respiration rate. The behavior of both soils differs for some SCG effects. In conclusion, SCG have a great potential to increase soil fertility and further investigations are needed in order to improve the use of SCG as amendment.

KEYWORDS:

• Biowaste
• coffee waste
• lettuce
• soil amendment
• waste reuse

Acknowledgments

This paper will form part of Ana Cervera-Mata’s doctoral thesis, which is being developed within the context of the “Nutrition and Food Sciences Programme” at the University of Granada. We thank Glenn K. Harding for proofreading the English-language manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by project AGL2014-53895-R from the Spanish Ministry of Economy and Competitiveness and by the European Regional Development Fund (FEDER).