Effects of Si fertilization on Si in soil solution, Si uptake by rice, and resistance of rice to biotic stresses in Southern Vietnam

Abstract

Silicon (Si) mitigates abiotic and biotic stresses for rice plants (Oryza sativa L.). Here, we test relationships between Si cycling, plant growth, and pest and fungal attacks in rice agroecosystems. We conducted a plot experiment on Si fertilization in a Southern Vietnamese paddy, where plant-available Si was inherently low. For two cropping seasons, we investigated the temporal dynamics of Si in soil solution, plant Si uptake, and the occurrence of leaf folders (Cnaphalocrocis medinalis) and rice blast caused by the fungus Magnaporthe oryzae. Silicon application increased Si concentrations in soil solutions collected in the field as expected from previous laboratory experiments. Soil solution Si concentrations were furthermore affected by Si uptake by plants and by recycling Si with rice straw ash. Silicon concentrations in rice leaves at tillering stage increased with increasing Si application. However, surprisingly, no relationship between Si in soil solution and Si concentration in straw at maturity stage was found. The occurrences of leaf folders and rice blast disease were mitigated by increased Si uptake. However, rice biomass production was not affected, probably because the biotic stress level was generally low. Our field data emphasize the importance of recycling crop residues in rice fields for the Si supply to plants, especially in regions with low Si availability. They furthermore show that under field conditions, the relationship between dissolved Si in soil solution and Si uptake by rice plants is not as straightforward as expected and thus needs to be further investigated.