Silicon Extraction in Fertilizer with Na2CO3 + NH4NO3 in the Autoclave.

An extraction method of silicon in slag and fertilizers was developed to quantify the potentially available Si for the plants. The method is based on the solubilization of the Si content materials in an alkaline extractor of Na₂CO₃ + NH₄NO₃. This study aimed at evaluating variations in the use of Na₂CO₃ + NH₄NO₃ as extractors of Si fertilizers. An experiment completely randomized with the rice culture in a Quartzipsamment soil and in a greenhouse was installed with 18 Si sources applied at a rate of 250 kg ha^-1 and a control with four replication. Another experiment was installed in factorial scheme (18 x 5) with 18 Si sources and five extractions of Si fertilizers and three replications in the laboratory. For this study, it was used four extractant solutions: Solution 1: Na₂CO₃ (0,1 mol.dm^-3) + NH₄NO₃ (0,2 mol.dm^-3); Solution 2 - Na₂CO₃ (0,1 mol.dm^-3) + disodium EDTA (0,03 mol.dm^-3) + NH₄NO₃ (0,2 mol.dm^-3); Solution 3 - Na₂CO₃ (0,1 mol.dm^-3) + disodium EDTA (0,03 mol.dm^-3) + NH₄NO₃ (0,2 mol.dm^-3) + C₂Na₂O₄ (0,06 mol.dm^-3) and; Solution 4 - Na₂CO₃ (0,1 mol.dm^-3) + disodium EDTA (0,03 mol.dm^-3) + NH₄NO₃ (0,2 mol.dm^-3) + CH₃COONH₄ (0,1 mol.dm^-3). The extractions with 4 solutions were induced by autoclave for 1 h at 120 °C. The solution 1 was also used in an extraction without application of autoclave but with rest of 5 days, thus totaling 5 extractions. The most efficient source for Si release to rice was Wollastonite [Ca₃(Si₃O₃)] followed by phosphorous slag and stainless steel slag, while the schist, blast furnace slag and silicate clay were the lowest on Si release. The autoclave was efficient in increasing the Si extraction, replacing the 5 days rest in the sample in solution. The highest extraction and better correlation between soluble Si and Si uptake by the rice crop was obtained in solutions with EDTA, but solution 2 showed greater extraction capacity of the Si sources.