Spent Coffee Grounds Applied as a Top-Dressing or Incorporated into the Soil Can Improve Plant Growth While Reducing Slug Herbivory

Finbarr G. Horgan (), Dylan Floyd, Enrique A. Mundaca and Eduardo Crisol-Martínez
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Finbarr G. Horgan: EcoLaVerna Integral Restoration Ecology, Bridestown, Kildinan, T56 P499 County Cork, Ireland
Dylan Floyd: School of Agriculture and Food Science, University College Dublin, D04 V1W8 Dublin, Ireland
Enrique A. Mundaca: Escuela de Agronomía, Facultad de Ciencias Agrarias y Forestales, Universidad Católica del Maule, Casilla 7-D, Curicó 3349001, Chile
Eduardo Crisol-Martínez: EcoLaVerna Integral Restoration Ecology, Bridestown, Kildinan, T56 P499 County Cork, Ireland

Agriculture, 2023, vol. 13, issue 2, 1-21

Abstract: Between 8 and 15 million tons of spent coffee grounds (SCG) are produced as global waste each year. To reduce waste to landfill, SCG are proposed as a carbon and nutrient source for degraded soils. SCG contain caffeine and other toxins that inhibit plant growth. However, they also repel slugs and snails. We examined whether partial decomposition can neutralize SCG to promote plant growth while maintaining anti-herbivore properties. We aged SCG for <1 to 14 months and also produced SCG-derived Black Soldier Fly ( Hermetia illucens ) frass. The aged SCG and frass were applied, either incorporated into soil or as a 1 cm top-dressing, to pots with radish and tomato seedlings. SCG treatments were also examined for direct (repellent) and indirect (plant-mediated) effects on four slug species ( Arion ater , Deroceras laeve , Derocerus reticulatum and Lehmannia marginata ). SCG of ≤7 months inhibited plant growth and development and reduced herbivory when incorporated into soil, whereas 14-month-old SCG promoted growth but had no effect on herbivory. When applied as a top-dressing, SCG at 7 months promoted growth and reduced herbivory through repellent and host quality effects—including possible systemic effects. Our results indicate that the benefits of SCG for radish and tomato growth and to reduce slug herbivory can be achieved simultaneously by applying partially decomposed SCG (aged for up to 8 months) as a top-dressing.

Keywords: black soldier fly; circular agriculture; frass; integrated pest management; repellence; systemic defenses (search for similar items in EconPapers)
JEL-codes: Q1 Q10 Q11 Q12 Q13 Q14 Q15 Q16 Q17 Q18 (search for similar items in EconPapers)
Date: 2023
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