The soils of Vanuatu are derived mainly from basic volcanic rocks. Soils are often young or frequently rejuvenated by deposition of new volcanic ash. The soils are differentiated into three main groups along a climatic sequence caused by the prevailing trade winds.
- In the wetter southeast ferralitic soils dominate. Ferralitic soils develop on weathered volcanic rock and are characterized by their high iron and aluminum oxide content, resulting in a reddish or yellowish color. They are acidic from prolonged weathering, low in natural fertility, and prone to leaching. Despite these challenges, ferralitic soils are well-drained, often with stony or gravelly subsoil and resilient to erosion, an advantage in regions with heavy rainfall.
Ferralitic soils roughly equate to Oxisols in US Soil Taxonomy. - In the drier northwest fersiallitic soils dominate. Fersiallitic soils also develop on weathered volcanic rock but are less acidic and have higher base saturation compared to ferralitic soils. This distinction results in improved nutrient availability in fersiallitic soils, making them generally more fertile. Additionally, fersiallitic soils often have a clayey texture, while ferralitic soils can vary in texture.
Fersiallitic soils are covered by both Ultisols as well as Alfisols in US Soil Taxonomy. - In the wet and humid (perhumid) highlands Andisols dominate. These are formed from volcanic ash and pyroclastic materials, which impart distinctive properties. Andisols are typically rich in organic matter and hold nutrients well due to their high cation exchange capacity. They have a dark colour and a granular texture. They retain moisture and are known for their fertility.
