Silicon, a Plant Beneficial Substance: Methods to Quantify Plant Available Silicon in Fertilizers.

In order to supply silicon (Si) to soils and plants, various forms of silicate materials are used.  Methods to quantify plant available Si from Si-based solid materials for use as fertilizers were tested.  Based on the correlation coefficients between the Si extractor and plant uptake, it was concluded that the best extractant for determining plant available Si in solid fertilizers is sodium carbonate-ammonium nitrate (Na₂CO₃ + NH ₄NO₃) with a 5 day sample resting period needed prior to Si analysis.  In Brazil, a soil incubation test for Si is also required, in addition to fertilizer Si analysis.

Until AAPFCO approved Si as a “plant beneficial substance” and a Single Lab Validation (SLV) of the 5-Day method was confirmed in Feb 2011, manufacturers could only list total Si on guarantee sheets and Si as a non-plant food ingredient.  Consequently, crop managers had no way of selecting a fertilizer based on plant available Si.  A brief overview of the AAPFCO approval process and the 5-Day method will be presented.  This method can now be used for Si product quality control including accurate solid Si fertilizer labeling, label guarantee compliance monitoring, and in selection of an appropriate Si fertilizer to meet end-user crop production needs.