ARS | Publication request: Effects of synthetic fertilizer on coffee yields and ecosystem services: Soil glomalin and parasitoids in a Costa Rican coffee agroecosystem

Submitted to: Journal of Crop Improvement
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 30, 2011
Publication Date: November 4, 2011
Citation: Banks, J.E., Cline, E.T., Castro, S., Urena, N., Nichols, K.A., Hannon, L., Singer, R., Chandler, M. 2011. Effects of synthetic fertilizer on coffee yields and ecosystem services: Soil glomalin and parasitoids in a Costa Rican coffee agroecosystem. Journal of Crop Improvement. 25:650-663.

Interpretive Summary: Synthetic fertilizer levels ranging from a 6.9% increase to a 53.5% decrease from normal were applied to coffee fields in Costa Rica. Soil glomalin (a thermo-stable glycoprotein produced by arbuscular mycorrhizal fungi) concentrations and parasitoid wasp abundance were then measured to determine the impacts of fertilizer levels on these agroecosystem indicators. Arbuscular mycorrhizal fungi assist in nutrient acquisition and disease control while glomalin assists in forming stable soil aggregates. These ecosystem services are critical to coffee production where slopes range from 4 to 66% and herbivorous arthropods are common. In addition, Hymenoptera (i.e. parasitoid wasps) are important in biological control agents, ovipositing in a wide variety of coffee pests, including lepidoptera and acarids. After six month, coffee yield and glomalin decreased with a reduction in fertilizer but parasitoid wasps increased. It was speculated that a reduction in fertilizer bolstered biological disease control to compensate for plant deficiencies, while glomalin production is more dependent upon plant growth.

Technical Abstract: We explored the relationships between synthetic fertilizer use, yield, and ecosystem services in a coffee agroecosystem in the Tarrazú region in the central highlands of Costa Rica. Working in nine farms ranging from 0.3 to 2.7ha in the CoopeTarrazú farmers' cooperative, we focused on two important indicators of ecosystem services: biological control agents and mycorrhizal fungi. Biological control agents (especially parasitoid wasps) are essential for population regulation of herbivorous arthropods that reside in coffee agroecosystems. Mycorrhizal fungi contribute to plant nutrition and disease resistance and produce a highly stable protein, glomalin, which is critical for soil aggregation. Soil aggregates hedge against erosion, particularly in sloping soils, by improving porosity. Slopes in this study ranged from 4 to 66%. We manipulated synthetic fertilizer levels in experimental plots ranging from 6.9% increase to 53.3% decrease in total N relative to control plots that received a standard amount of fertilizer. The effects on coffee yields, soil glomalin production by mycorrhizal fungi, and wasp diversity were examined. Yield and glomalin decreased, but parasitoid diversity increased with greater reductions in fertilizer application six months after application. Reducing fertilizer use may bolster biological control assemblages, while glomalin is more directly dependent on plant production.