Soil and Coffee

Coffee is grown from the Tropic of Cancer to the Tropic of Capricorn. At these latitudes, constant processes of weathering and erosion in the warm humid conditions have leached the soils of essential nutrients. The Encyclopedia of Soils in the Environment, the tropical soils section describes common nutrient deficiencies in tropical soils as, “The most frequent limitations result from insufficient plant-available nitrogen, phosphorus, potassium, calcium, or magnesium” (Buol 187-195). The journal goes on to explain about how each of these nutrients are added to soil through weathering of minerals and how they can be bound up or leached to the extent that they’re no longer available to plants; For example, Potassium comes from micas and feldspar which are easily weathered and “consequently are seldom present in materials that have been repeatedly transported and deposited on the land surface”(187-195). Phosphorous tends to get bound up very tightly to Iron and Aluminum and is virtually inaccessible to plants. Soil that is nutrient rich is very valuable for plant life and thus agriculture, humans, and coffee production in the tropics. We’ve frequently mentioned in class how volcanic debris are very important sources of soil nutrients in the tropics for both coffee and cacao. Buol adds areas where tectonic uplifting has raised “limestone, base-rich igneous, rock and metamorphic rock” and “floodplains and deltas to the list” of important agricultural areas. These are the mineral-fertile areas where agriculture makes a lot of sense. The two cultivated varieties Arabica and Robusta can be grown at a wide elevation range which means coffee could potentially take advantage volcanic soils at high altitudes of or rich soils at lower altitudes. Both species can also be grown as part of an agroforestry system. We found a couple interesting studies on the interaction between soil and different coffee growing systems: agroforestry or monoculture. One measured carbon sequestration in soil around coffee production. This study found that soil organic carbon was significantly higher in an agroforestry system than a monoculture system and that Robusta grown together with non fruit trees had the highest soil organic carbon concentration of any of the coffee systems they looked at (Tumwebaze & Byakagaba Agriculture, Ecosystems & Environment). A study on water erosion in volcanic soils in coffee farms in Sumatra found that “The runoff coefficient under monoculture coffee remains on average significantly higher (10–15%) than under forest (4%) or under shade coffee systems (4–7%)”(Verbist et. al. CATENA). A study on Phosphorous in soils in coffee farms found that Agroforestry coffee systems had a greater proportion of organic phosphorous to inorganic phosphorous. (Cardoso et. al. Agroforestry systems).