In the Central Valley of Costa Rica in the Department of Heredia, I investigated the soil chemical properties and microbial communities under four native shade tree species in a coffee agroforestry system. In the second year of the study, Effective Microorganisms, a microbial inoculant, was applied to examine its effect on soil chemistry. The shade tree species included in this study were Anonna muricata L., Diphysa americana Mill., Persea americana Mill., and Quercus spp. L. Plots measured 20 by 30 meters and were replicated three times for each shade tree species except for Quercus spp., which only had two replications. Twelve composite soil samples were collected from each plot in 2008 and again in 2009, and twelve composite foliar samples were taken from the coffee plants in each plot in 2008. The results of this study indicated that the species of native shade tree had a significant effect on soil ammonium-N, nitrate-N, total dissolved nitrogen and magnesium. Sun or shade position had a significant effect on dissolved organic nitrogen and dissolved organic carbon. The species of native shade tree also had a significant effect on the composition of soil microbial communities. PLFA analysis revealed a significant difference in soil fungi abundance in soil samples from Annona plots relative to those from Persea plots. Effective microorganisms in combination with the tree species, as well as in combination with species and sun or shade position, had a significant interaction effect on soil ammonium-N, with the EM-treated plots showing higher concentrations of soil ammonium-N. There was a significant positive correlation between soil pH and foliar calcium, as well as soil dissolved organic nitrogen and foliar %N, at p< 0.01. This study suggests that Quercus spp. is a tree species that may help to regulate the cycling of nitrogen in the coffee agroecosystem. Annona muricata appears to inhibit the action of some fungal species and may reduce the occurrence of fungal pathogens in the soil, although the present study did not explore this issue. Although Diphysa americana is a legume, it does not appear to increase the amount of soil nitrogen in the vicinity of the coffee plants themselves. All four tree species in this study improve coffee soils by increasing soil concentrations of dissolved organic nitrogen and dissolved organic carbon. Coffee yield data and long term observations on the health of the coffee plants would clarify whether one of these species is particularly beneficial, from an agronomic perspective, for the productivity of this coffee agroecosystem.

Coffee is, together with cacao, the crop most commonly cultivated under shade trees in order to cope with physiological stress (as drought and sun radiation) and erosion as well as to generate additional income for the farmer. However, today this agroforestry coffee management is increasingly transformed into industrial plantation with little or no shade using varieties that tolerates full sun and can be planted with higher density. This conversion most often brings an intensified use of external input, such as fertilizers and pesticide, and a reduction in biodiversity as well as long term soil fertility. The objective of this study was to examine whether the inclusions of trees in coffee cultivations favour soil fertility and how it affects the output of the system. The aspect of output was not only delimited to the weight of coffee yield but take a broader perspective that comprises the farmer’s economy. This was done by conducting a review of previous research on the subject combined with a field study performed at six smallholding coffee farms with different levels of shade in Colombia from November to December 2014. The results of the field study serve as a site specific example and are discussed in relation to previous findings. Soil samples was taken at the farms and analysed for organic matter, soil moisture, respiration rate and acidity. The hypothesis was that the inclusion of trees in coffee cultivations can enhance the long term soil fertility when compared to monoculture systems. And also that agroforestry coffee can bring an increased safety for the farmer in terms of income, when compared to monoculture coffee. No general conclusions could be drawn based on the results from the field study; however the results show that a change from agroforestry management to monoculture management in coffee cultivations in Colombia can have a significant negative effect on soil respiration rate. Furthermore the study highlights the importance of taking into account the specific characteristics of the location and the management of the investigated farm when making conclusions about the effects of agroforestry on soil fertility. It is also concluded that long term studies, extending over at least a year, is necessary to fully see the effects of the cultivation practice on soil fertility.

This study investigated sustainability challenges and benefits for coffee farming with different amounts of shade management in Colombia. Data was collected from literature studies, quantitative soil analyses and interviews with farmers and other experts. The results show that shade management of coffee farms does increase ecological sustainability, but in general gives lower yields of coffee. However, shaded coffee systems have the potential of increasing economic resilience for farmers by providing diversified income possibilities. The low and fluctuating coffee price of the global market has shown to be a major challenge of sustainability for Colombian small scale coffee farms. In addition a participatory sustainability assessment of soil quality and crop health was conducted with four farmers. The results from these assessments were compared with results from quantitative analyses of soil compaction, microbiological respiration rate and organic matter content in order to evaluate the analytical reliability of the assessment. The results of the participatory assessment were shown to correlate quite well to the quantitative soil analyses. When participatory methodology was evaluated from experiences in field and literature, it was found to be an important approach in facilitating sustainability learning in local contexts. / En esta investigación se examinaron los retos y beneficios de la sostenibilidad en la producción del cultivo de café con diferentes niveles de sombra en Colombia. Los datos se colectaron de estudios de literatura, análisis de suelo y entrevistas con agricultores y expertos en el tema. Los resultados indican que el manejo con sombra incrementa la sostenibilidad ecologica de las fincas cafeteras, y esto, tiene la posibilidad de incrementar la resiliencia económica para los agricultores al ofrecer oportunidades para una producción diversificada de ingresos. El precio bajo y fluctuante del café en el mercado mundial ha demostrado ser un importante reto para la sostenibilidad de las fincas de los campesinos colombianos. Además, se realizó una evaluación de la sostenibilidad participativa de la calidad del suelo y la salud de los cultivos con cuatro agricultores. Los resultados de esta evaluación se compararon con los resultados de análisis cuantitativos: de la compactación del suelo, la tasa de respiración microbiológica y contenido de materia orgánica, con el fin de evaluar la fiabilidad analítica de la evaluación participativa. Se demostró que los resultados de la evaluación participativa tienen una estrecha relación con el análisis cuantitativo del suelo. Cuando la metodología participativa se evaluó a partir de las experiencias propias en el campo y la literatura, se encontró que puede ser un enfoque importante para facilitar el aprendizaje de sostenibilidad para los contextos locales.

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