Effect of silicon on the growth and phosphorus uptake of rice

A pot experiment was conducted to measure the effect of silicon on phosphorus uptake and on the growth of rice at different P levels. Rice (Oryza sativa L. cv. Akebono) was cultured in Kimura B nutrient solution without and with silicon (1.66 m M Si) and with three phosphorus levels (0.014 m M P, low; 0.21 m M, medium; and 0.70 m M, high). Shoot dry weight with Si (+Si) in solution increased with increasing P level, while shoot weight without Si (-Si) was maximum at 0.21 m M P, suggesting that +Si raised the optimum P level for rice. +Si increased shoot weight more when P was low or high than when P was medium. The concentration and amount of inorganic P in shoots increased with increasing P level. +Si did not significantly decrease P uptake by rice at 0.014 m M P, however, uptake at 0.21 and 0.70 m M P was 27 and 30 percent less than uptake with -Si, respectively. In -Si with 0.21 and 0.70 m M P, inorganic P in shoots was more than double the concentration in shoots grown in +Si solutions. The Si concentration in shoots decreased slightly with increasing P level, although Si uptake was not significantly affected by P. +Si decreased the uptake of Fe and Mn by an average of 20 and 50 percent, respectively, thus P/Mn and P/Fe ratios increased in the shoot when P was low. From the results above, the beneficial effect of Si on the growth of rice was clearly shown when P was low or high. This effect may have resulted from decreased Mn and Fe uptake, and thus increased P availability within P deficient plants, or from reduced P uptake when P was high.