Residual effect of rice husk ash on availability of silicon and phosphorus in soil

Abstract

Phosphorus (P) is a limiting nutrient to agricultural production. Coming from non-renewable sources, studies that point to alternative materials that provide P may be of great importance in the near future. In this sense, rice husk ash (RHA) can be a viable option due to her composition, rich in silicon (Si), that can increase soil phosphorus availability. This investigation aimed to evaluate the residual effect of rice husk ash in the phosphorus and silicon soil availability. To this end, a field experiment was conducted with ten rice husk ash dosages 0, 10, 20, 30, 40, 60, 80, 100, 120 e 140 t ha^-1 where  soil sampling was collected at 15 days after ash incorporation, in the layers 0,00 – 0,10 m and 0,10 – 0,20 m. To evaluate residual effect it was used four rice husk ash dosages from initial experiment referring to 0, 30, 60 e 120 t ha^-1 where four more samples are done at 211, 400, 517 and 804 days after ash incorporation. Available phosphorus was determined by the double acid extraction method (Mehlich-1) while silicon was determined by the method that uses acetic acid as extractor. Results showed that rice husk ash increases soil phosphorus and silicon availability; the increased of soil silicon available, extractable by acetic acid, is equivalent to a fraction of a maximum of 0,08% of total silicon from rice husk ash; the residual effect of RHA in the silicon availability is higher than in the phosphorus availability; as phosphorus source the residual effect of RHA is lower than that of soluble mineral fertilizers such as acidulated superphosphates and, it’s possible that RHA causes the leaching of phosphorus in soils with low nutrient adsorption capacity.