INFLUENCE OF SILICON FERTILIZER GRADES ON BLAST AND BROWN SPOT DEVELOPMENT AND ON RICE YIELDS

Calcium silicate slag, applied as a source of plant-available silicon on silicon-deficient soils, reduces plant disease and increases yields of rice. The purpose of this experiment was to evaluate performance of three forms of slag and three rates of application on disease and yield. Calcium silicate slag was applied at 0, 2.5, and 5.0 Mg/ha as a fine-grade material (100% < 0.15 mm), a standard-grade material (90% < 2.36 mm), or as pellets (100%; > 1 mm and < 3.35 mm) made from the fine-grade material. Brown spot (caused by Bipolaris oryzae) severities decreased over the controls by 48-80%, 33-60%, and 2-23% for the fine, standard, and pelletized forms, respectively, in 1990 and 1991. Blast (caused by Pyricularia grisea) severities also decreased by 50%, 23%, and 4% for the fine, standard, and pelletized forms, in comparison with the control in 1991. Plant tissue silicon content and grain yields increased with increasing slag rates. Silicon content in plant tissue increased 131-246%, 208-122%, and 108-192% with the fine, standard, and pelletized forms, and yields increased 20-26%, 18%, and 4-11% for both years. The fine grade of silicon fertilizer was best for increasing silicon content and grain yields and for reducing the severity of brown spot and blast. These results are encouraging. since lower slag rates of finer grades may be used to reduce production costs while enhancing integrated management of several important rice diseases.