Low silicon (Si) content in rice, sugarcane and other Si-accumulating crops can adversely affect crop performance because it creates reduced tolerance to both abiotic and biotic stresses. Assessing the Si status of a crop typically depends upon accurately measuring Si accumulation in plant tissue. Methods involving wet digestion of plant tissue followed by colorimetric determination of Si have proven attractive because they are both rapid and do not require costly, specialized instrumentation. Some popular wet-digestion methods are reported to provide highly variable and inconsistent results. A systematic study to identify and address the sources of variability associated with wet digestion for Si analysis found that modifications that reduce excessive foaming during wet digestion of plant tissue in strong alkali and peroxide significantly reduce variability. Unstable and variable color development associated with the molybdenum blue reaction is a concern in the colorimetric determination of Si in digests. Experiments showed that 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 inductively coupled plasma-optical emission spectroscopy (ICP-OES) analysis. A two-phase wet-digestion procedure is described for Si tissue analysis that is robust, accurate, and precise and requires equipment commonly found in most agricultural laboratories.

A gronomy J our n al • Volu me 102 , I s sue 2 • 2 010 523 ABSTRACT Low Si content in rice (Oryza sativa L.), sugarcane (Saccharum offi cinarum L.), and other Si-accumulating crops can adversely aff ect crop performance by increasing susceptibility to abiotic and biotic stresses. Although it is generally assumed in the United States that soils containing appreciable amounts of silicate clays supply adequate Si to meet crop demands, there is little evidence to support this assumption. A survey was conducted to assess the Si status of rice plants at mid-tiller (Y-leaf) and at harvest (straw) in 97 rice fi elds located throughout the rice-growing regions of Louisiana. On average, Y-leaves contained 30.5 ± 7.8 g Si kg -1 , whereas mature rice straw contained 54.7 ± 12.7 g Si kg -1 . Low early season Si assimilation occurred in nearly all rice fi elds, whereas only 36% contained mature straw with <50 g Si kg -1 , a level commonly used to indicate suffi ciency. Late-season defi ciencies were limited to fi elds in extreme southwest Louisiana where soils tend to be strongly acidic and have a long history of rice production.

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