Tree trials conducted recently in Kiribati to identify fast-growing trees for agroforestry have revealed exotic species adapted to atoll environments. In general, atolls to the North of the Equator receive more rainfall than atolls to the south of the equator. Average soil particle size is extremely large compared to other igneous derived soils and therefore the soil is highly permeable with a low water holding capacity. In Kiribati, soils are shallow, well drained and deficient in nitrogen, potassium, and trace elements, especially iron, manganese, zinc and copper. The organic matter in the thin top-soil layer is almost totally responsible for nutrient recycling and exchange between plants and soil.
Iron deficiency is a common constraint to plant growth on atolls.
Tree Trials Trials to test exotic species with agroforestry potential were established in Kiribati in 1992 and 1994 in collaboration with the Nitrogen Fixing Tree Association's Agroforestry Information Service. Native, naturalized and exotic species were included in the trial. Non-NFTs tested were Delonix regia and Eucalyptus camaldulensis . Sophora tomentosa and C. equisetifolia grow well on most atoll soils with a minimum of external inputs. Pithecellobium dulce is surviving but is stunted and chlorotic.