Quantitative assessment of plant‐available silicon extraction methods in rice paddy soils under different management

Abstract

AbstractAddition of Si into paddy soil is an effective way to increase plant Si and decrease the uptake of stress‐causing metal(loids) in rice (Oryza sativa L.). However, there are numerous methods to estimate plant‐available Si and some have limitations when Si has been applied. We evaluated four published extraction methods (1‐h CaCl2, 16‐h CaCl2, CH3COOH, and PO4) and a 4‐h CaCl2 extraction method. We related soil‐extractable Si to plant Si in Si‐rich rice straw and husk. Samples were collected from a 3‐yr field study in which rice was grown under a range of soil redox values (via water management) or continuously flooded and receiving different Si amendments. Straw Si concentration was a more stable measure of soil Si than husk Si concentration, regardless of the extraction method. Of the four published methods tested, the 16‐h CaCl2 extraction explained most of the variation in straw Si concentration (R2 = 0.67), followed by PO4 (R2 = 0.50), CH3COOH (R2 = 0.26), and 1‐h CaCl2 (R2 = 0.13). The Silicate‐treated soils deviated from linear relationships with straw Si for the CH3COOH and PO4 extractions. The 16‐h CaCl2 extraction method explained over 80% of the variation in the 4‐h extraction method (R2 = 0.82). Moreover, the 4‐h CaCl2 method explained nearly 60% of the variation in straw Si (R2 = 0.58), similar to the 16‐h CaCl2 method. We recommend using the 4‐ or 16‐h extraction methods to assess plant‐available Si in rice paddy soil, as these perform well regardless of soil management.