On the Use of Silicon as an Agronomic Mitigation Strategy to Decrease Arsenic Uptake by Rice

Rice is a staple food for over half the global population and its sustainable production is directly linked to global food security. Rice yield and human health are threatened by arsenic (As) contamination in rice grain. Arsenic enters rice mainly because the geochemical parameters under which rice is conventionally grown mobilize soil As, and because three of the four predominant As species are taken up by rice roots along the efficient silicon (Si) transport pathway. Several strategies have been explored to decrease toxic As uptake by rice including water management, plant breeding and genetic approaches, and Si management. Water management is effective at decreasing As uptake by rice and decreases methane (CH4) emissions, but may decrease rice yield and increase grain cadmium (Cd) content and nitrous oxide (N2O) emissions. Plant breeding or genetic approaches aim to select for or engineer cultivars that limit grain As. Si management aims to increase plant-available Si to compete with As for root uptake. Addition of Si improves rice yield, particularly when plants are stressed with As. Si also affects As speciation, both in the porewater and in the plant, Fe plaque mineral composition and quantity, and greenhouse gas emissions, although performance is amendment specific. More research is needed to mechanistically understand the diverse interactions between Si and As in sorption, porewater chemistry, microbial processes, plant uptake of As, and grain accumulation and speciation of As. Because of the plethora of beneficial effects of Si, Si holds tremendous promise as a sustainable soil amendment in the effort to mitigate rice accumulation of As.