The Influence of Agroforestry on Soil Fertility in Coffee Cultivations : A Review and a Field Study on Smallholding Coffee Farms in Colombia

Abstract: 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.