High rice husk ash doses applied to the soil can lead to phosphorus water contamination.

The goal of this work was to evaluate the rice husk ash (RHA) effect on soil phosphorus (P) adsorption and to analyze the probable consequences of these in the parameters that affect P availability to the plants and the risk of soil P loss by superficial run-off. For this, a factorial experiment was conducted in laboratory with samples of two soils (factor A: Hapludult and Hapludox) that were submitted to five doses of RHA (factor B: 0; 25; 50; 75 and 100 g RHA kg of soil). The experimental units were plastic pots with 200 g of air-dry fine earth from horizon A of each soil.