Silicon and Heavy Metals Dynamics in Paddy Soils and Uptake By Rice Applied with Silicate Slag.

Paddy rice production enhances heavy metals availability in soils and their uptake by rice. This study evaluates the effect of silicon (Si) fertilization on Si and heavy metals dynamics in soils and their uptake by rice. Field trials were established in 12 sites across Louisiana from 2013 to 2015. Treatments included five silicate slag (14% Si) rates at 1, 2, 4, 6, and 8 Mg ha^-1, two lime treatments of 2 and 4 Mg ha^-1_, and a control. Treatments were arranged in a randomized complete block with four replications. Soil samples collected post-harvest were extracted using seven different extraction procedures and sample extracts were analyzed for Si using the molybdenum blue colorimetry (MBC) procedure. Heavy metals were extracted using Mehlich-3 and 0.1 N HCl procedures and sample extracts were analyzed for heavy metals by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) procedure. Straw and panicle were subjected to oven induced digestion followed by MBC to determine their Si content. Panicle samples were also digested using the HNO₃-H₂O₂ digestion; heavy metals in digested samples were analyzed by ICP-OES. Analysis of variance and correlation analysis were performed for all measured variables using SAS 9.4. Soil pH was significantly increased in several sites by as much as 1.4 units (p< 0.05) by silicate slag application. Soil Si concentration determined by 0.5 M acetic acid was negatively correlated with panicle arsenic (As) (r = -0.53) and cadmium (Cd) (r = - 0.68). Straw and panicle Si were negatively correlated with panicle As (r = -0.41 and r = -0.33) respectively; and panicle Si was negatively correlated with its Cd content (r = -0.39). However, manganese (Mn) content of panicle was positively correlated with its Si content (r = 0.35). Results suggest that Si fertilization could be essential in improving the grain quality of paddy rice.