EXTRACTORS FOR ESTIMATING PLANT AVAILABLE SILICON FROM POTENTIAL SILICON FERTILIZER SOURCES

Methods to quantify plant available silicon (Si) from Si-based slags for use as fertilizers are not well defined. Although it is possible to estimate total Si from a potential Si fertilizer source; this approach does not represent how much Si is available for uptake by the plant. In this study, Si was extracted from ten sources [Wollastonite W10; calcium silicate slag from the US; calcium silicate from Canada; magnesium silicate; Excellerator; silican gel; 00-00-12 + Si (liquid source) and three types of potassium silicate with different concentrations in the liquid form, K53; K120 and AgSilTM25] using each of the following seven methods: hydrochloric acid (HCl) plus hydrofluoric acid (HF) extraction, leaching column; sodium carbonate (Na2CO3-10 g L-1) + ammonium nitrate (NH4NO3-16 g L-1); citric acid (50 g dm-3 or 5%); hydrochloric acid (0.5 N); neutral ammonium citrate (NAC); and resin (Amberlite IRC-50, pK 6.1). All the Si-containing products were added to pots at rates equal to 600 kg ha-1 of Si based on the total Si extracted. Poa trivialis cv. 'Darkhorse' was grown for 24 days with these sources to determine Si plant uptake. Based on the correlation coefficients, the best extractor for available Si in solid fertilizer was determined to be Na2CO3 + NH4NO3, while for liquid fertilizers, the total Si (HCl + HF) was found to be the best. Consequently, regulatory agencies now have two extractors for estimating the plant available Si from fertilizers depending on the physical property of the material (solid or liquid).