Availability of rice straw Si to rice plants

Abstract A pot experiment was conducted to estimate the availability to rice plants of Si contained in rice straw. To separate the effect of straw application on Si availability in soil, two kinds of rice straws, which contained 15.5% (+ Si straw) and 0.2% SiO2 (—Si straw), were used at a rate of 1% of air-dry soil, respectively. Rice plants were cultivated twice during a period of 2 months each. Results of the two harvests indicated that +Si straw application increased the Si concentration in the percolating water, the Si content of rice shoots, and soil-available silicate. However, compared to the Si contained in the added straw, the release of Si from the +Si straw was only about 6% in the first cultivation, and 3% in the second cultivation, respectively. The — Si straw application was not associated with any of the effects observed in the +Si straw application. Successive water extractions showed that the solubility of Si in the +Si straw was lower than that of silica gel, but much higher than that of opal. These facts suggest that the short term availability of Si in the straw applied to the soil is low and the application of materials with a higher availability of Si such as slags may be desirable for satisfactory growth of rice plant.