Organically managed coffee agroforests have larger soil phosphorus but smaller soil nitrogen pools than conventionally managed agroforests
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The cultivation of crops in the presence of trees (agroforestry) and organic agriculture are management strategies thought to reduce nutrient losses to the environment and increase soil organic matter. Little is known, however, about the differences between organic and conventionally managed agroforests. This research examines how soil nutrient pools and mechanisms for nutrient retention may vary between these two different types of coffee agroforests. We determined variation in soil nutrient pools and nutrient retention capacity among (1) coffee farms in Costa Rica receiving mineral (conventional management) and organic inputs (organic management) and (2) different combinations of shade tree species. Soil nutrient pools and retention capacity were altered by fertilizer management. Soil nitrogen (N) and carbon (C) pools were significantly larger in conventional agroforests, but C:N ratios were similar among agroforests. Soil phosphorus (P) pools were significantly higher in organic agroforests. Overall, C and N concentrations were strongly positively correlated with oxalate-extractable aluminum concentrations. We did not observe many strong species effects; however, soil cation exchange capacity was higher under Coffea–Musa combinations than under Coffea and N-fixing Erythrina combinations. Thus, mechanisms are in place to promote nutrient retention in agroforestry systems, but these mechanisms can be altered by management practices with consequences for long-term nutrient storage.
KeywordsAgroforestry Coffee Nutrient pools Nutrient retention capacity Organic agriculture
We would like to acknowledge the financial contributions of the Jefferson Scholars Foundation, the Raven Society, the Bankard Fund for Political Economy, the Center for Undergraduate Excellence, and the University of Virginia, to this research. Gabriela Soto facilitated the logistics of the fieldwork. We are grateful to our field and lab team at CATIE: Alejandra Hernández Guzmán, Amanda Schwantes, Blanca Salguero Londoño, Mauricio Scheelje, and Patricia Leandro. Finally, we would like to acknowledge the farmers of San Juan Norte, San Juan Sur, and Colorado for giving us access to their farms and welcoming us into their homes.
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