Impact of inorganic and plant-based silicon amendments on arsenic accumulation, yield, and greenhouse gas emissions in rice (Oryza sativa L.) under elevated soil arsenic conditions

Seyfferth, AngeliaArsenic (As) is a ubiquitous contaminant in the world’s rice supply due to the practice of paddy (flooded) agriculture and addition of As to paddy soils through irrigation water and pesticide use. Both inorganic and organic forms of As contaminate rice, but inorganic As is a recognized human carcinogen and threatens human health accordingly. While organic As species are less toxic to humans, they are suspected agents of Straighthead disorder in rice, which reduces yield. Silicon (Si), a beneficial nutrient for rice that increases yield and decreases inorganic As accumulation in grain, could mitigate the negative impacts of As on rice production and human health. Although Si fertilization could be accomplished by using rice straw as a soil amendment, labile C additions (i.e., straw) to rice paddies have been implicated with increased grain As concentrations and CH4 emissions. Recent work has demonstrated the potential of fresh rice husk (FH) as a Si-rich amendment that decreases grain As and without increasing CH4 emissions. It is unknown, however, how FH and other Si-rich amendments would perform in a soil elevated in As. In this experiment, we evaluated FH, rice husk ash (RHA), and calcium silicate (CaSiO3) as soil amendments for their effects on Si fertilization, grain-As accumulation, rice yield, and emissions of CO2 and CH 4 in a pot experiment utilizing a well-weathered (i.e., Si-depleted soil) contaminated with As and irrigated with As-contaminated water to simulate locales in South and Southeast Asia (e.g., Bangladesh). Using synchrotron techniques, we examined the impacts of the amendments on root Fe-plaque as a driver for differences between treatments in terms of As uptake. The results indicate that using FH as an amendment holds promise for decreasing grain As and increasing rice yield in As-contaminated soils.University of Delaware, Department of Plant and Soil SciencesM.S