Carryover effects of silicon‐rich amendments in rice paddies

Abstract Rice ( Oryza sativa L.) readily accumulates the nutrient silicon (Si) and the toxin arsenic (As), elements that can interact antagonistically both in the plant and in the soil. Thus, many studies have been performed where Si‐rich materials are incorporated into soils to increase plant‐available Si and thereby decrease plant As. However, studies have not examined the dissolution kinetics of Si from Si‐rich materials over multiple seasons and the resulting effects on rice systems. Here, we analyzed the porewater chemistry, CH 4 emissions, and rice elemental concentrations from rice paddies in Year 2 that had been amended with Si‐rich materials (silicate fertilizer, rice husk, and charred rice husk) in Year 1. After two crop cycles, plant‐available Si and plant Si concentrations remained elevated in Si‐amended paddies. Silicon‐rich amendments also decreased plant As concentrations, although this effect was only observed in the vegetative tissues. Husk treatment resulted in the lowest porewater redox, highest CH 4 emissions, and highest porewater inorganic As. Porewater concentrations and dynamics of inorganic As, dimethylarsinic acid (DMA), and trimethylarsine oxide (TMAO) differed for each amendment, but Si‐rich amendments exhibited elevated inorganic and organic As early in the growing season. These Si‐rich amendments can continue to provide Si and impact rice systems two growing seasons after application.