The main agricultural soils are; red clay soil (rojo arcillosos, ultisols), trumao and ñadi. Some red clay soils are planted with Eucalyptus globulus. In the middle course of Bío Bío River, in the northern part of Zona Sur, soils are sandy with a coarsening trend towards the Andes. Soils of the Chilean Coast Range are mostly derived from metamorphic rock. These soils are usually poor in phosphorus, potassium and have toxic levels of aluminium. Often, these soils have poor drainage and their thickness is highly variable even at scale of tens of meters.