SILICON AVAILABILITY AND RESPONSE OF RICE AND WHEAT TO SILICON IN CALCAREOUS SOILS

The 23 surface paddy soils (0-20cm) representing varying range of calc ium carbonate (CaCO3) were collected to evaluate silicon (Si) supplyin g power and the factors which affect Si availability. A pot experiment and consecutive four-year field trials were also carried out in this study to investigate the response of rice (Oryza sativa L. cv Wuyujing No. 3) and wheat (Triticum aestium L. cv Yangmai No. 5) to Si-contain ing materials applied to the calcareous paddy soils. The result indica ted that the available Si contents (sodium acetate-extractable SiO2) o f the Soils surveyed were much higher than the accepted critical value . Stepwise regression analysis showed that pH value, clay, and CaCO3 c ontents significantly affected the available Si content. The pot exper iment indicated that the grain yield, spike number, and filled grain p ercentage and ratio of grain/shoot of the Si-treated rice markedly inc reased as compared to the control, but Si added had little effect on t he shoot dry matter yield and 1,000-grain weight. On the other hand, t he available and water soluble-Si contents in the Si-treated soils wer e obviously higher than those of the untreated soil both at tillering and elongation stages. The same was true for the TCA (Trichroloacetic acid)-soluble Si and total Si contents in rice plants. The Si content in the percolating water also increased in the Si-treated soils as com pared with the control-especially during the first week after rice tra nsplanting. Consecutive four-year field trials indicated that Si appli ed increased the rice and wheat yields by 4.6-20.7% and 4.1-9.3%, resp ectively. The added Si-containing materials enhanced the resistance of rice and wheat against fungal and bacterial attacks and lodging. The results obtained in this study suggest that calcareous paddy soils whi ch have a high content of sodium acetate extractable-Si were still Si deficient and the available-Si extracted by this extractant might over estimate the Si-supplying power of these calcareous soils. It will eit her be necessary to develop a new extractant suitable for evaluating t he available-Si status of calcareous soils or to modify the level of a vailable Si in these soils above which rice responses to Si fertilizer will not be obtained.