Influence of rainfall on properties of soils developed on granite in Portugal

Abstract

A synthesis of the physical, chemical, and mineralogical properties of soils developed on granitic rocks under different climatic conditions in Portugal was performed, including soil classification. Mean annual rainfall, the climate parameter best correlated with the variability of soil properties, was analyzed in terms of relationships with several soil properties (organic C content, soil pH, nature of the exchange complex, SiO2/Al2O3 ratio, selective extractions of Fe and Al, P retention, content and nature of clay fraction). Organic matter was the soil property best correlated with the variability of soil physical properties (porosity, bulk density, and available water), exchange capacity, exchangeable acidity, and extractable Al and Fe. In wetter areas, amorphous Al and P retention occurred in large amounts and were well correlated with each other. The effect of rainfall was especially marked for the range 500–1,200 mm per year. The amounts of rainfall corresponding to 800 and 1,200 mm appeared to sep...