Assessing the silicon status of rice (Oryza sativa)

Low silicon (Si) content in rice, sugarcane and other Si-accumulating crops can adversely affect crop performance due to reduced tolerance to both abiotic and biotic stresses. This research had two specific objectives relative to Si in Louisiana rice: develop a digestion procedure for Si tissue analysis that is robust, accurate, precise, and requires equipment commonly found in most agricultural laboratories; and survey the Si status of rice plants at mid-tiller (Y-leaf) and after harvest (straw) throughout the rice-growing regions of Louisiana. Assessing the Si status of a crop typically depends upon accurately measuring Si accumulation in plant tissue. While wet-digestion methods have several advantages for Si analysis, the accuracy and precision of these methods are doubtful. A systematic study showed that control of excessive foaming during digestion of plant tissue significantly reduced variability and increased recovery. The inclusion of ammonium fluoride to facilitate the release of polysilicic acid prior to colorimetric determination results in reproducible readings that stabilize within 60 min and remain stable for at least 5 h. With this modification, the accuracy and precision of values obtained colorimetrically are comparable or superior to those obtained by ICP-OES analysis. A detailed survey of the Si status of rice grown in the Major Land Resource Areas (MLRA) throughout Louisiana was created to identify areas where possible Si deficiencies occur and where responses to Si fertilization would most likely result in economic responses. Low early season uptake occurred in nearly all rice fields included in this study, though by harvest, only 36% of the fields contained less than 50 g Si kg-1. Parishes showing the lowest seasonal Si uptake were located within the Gulf Coast Prairies MLRA in the southwest corner of Louisiana. Significant correlations (p\u3e0.05) were found between air dry pH and tissue Si at both early and late season, but no relationships were evident between dissolved Si in irrigation flood water or soil pore water and Si uptake by rice