Soil properties governing phosphorus adsorption in soils of Southern Brazil

Abstract Southern Brazil is carachterized by soil classes with contrasting mineralogical composition and chemical behavior that directly affect the P adsortion capacity. This study is a first detailed regional assessment of the main factors (including mineralogical composition, total organic C, and specific surface area) that determine P adsorption in 60 representative soils of southern Brazil under natural vegetation. Most soils showed medium to clay texture. Organic C increased with increasing altitude and rainfall but decreasing temperature. Kaolinite, goethite and hematite were the dominant minerals in the highly weathered soils (Ferralsols and Nitisols), associated with smaller amounts of 2:1 clay minerals, quartz and gibbsite. In soils with a textural gradient (Acrisols, Alisols and one Plinthosol), minerals in the clay fraction consisted of kaolinite and quartz together with lower proportions of Fe oxides, 2:1 clay minerals and mica. The less weathered soils (Cambisols, Chernozems, Vertisols and Luvisols) abounded with kaolinite and 2:1 clay minerals in addition to goethite, ferrihydrite and quartz. P adsorption was positively correlated with clay and organic C content and specific soil surface area. The mineral most strongly influencing P adsorption was gothite, and hematite and gibbsite to a lesser extent.