Silicon availability and response of rice and wheat to silicon in calcareous soils

Abstract

The 23 surface paddy soils (0–20cm) representing varying range of calcium carbonate (CaCO₃) were collected to evaluate silicon (Si) supplying 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‐containing materials applied to the calcareous paddy soils. The result indicated that the available Si contents (sodium acetate‐extractable SiO₂) of the soils surveyed were much higher than the accepted critical value. Stepwise regression analysis showed that pH value, clay, and CaCO₃ contents significantly affected the available Si content. The pot experiment indicated that the grain yield, spike number, and filled grain percentage and ratio of grain/shoot of the Si‐treated rice markedly increased as compared to the control, but Si added had little effect on the shoot dry matter yield and 1,000‐grain weight. On the other hand, the available and water soluble‐Si contents in the Si‐treated soils were 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 compared with the control—especially during the first week after rice transplanting. Consecutive four‐year field trials indicated that Si applied increased the rice and wheat yields by 4.6–20.7% and 4.1–9.3%, respectively. 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 which have a high content of sodium acetate extractable‐Si were still Si deficient and the available‐Si extracted by this extractant might overestimate the Si‐supplying power of these calcareous soils. It will either be nessesary to develop a new extractant suitable for evaluating the available‐Si status of calcareous soils or to modify the level of available Si in these soils above which rice responses to Si fertilizer will not be obtained.