Residual Effects of Calcium Silicate in Tropical Soils: I. Fate of Applied Silicon During Five Years Cropping

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Abstract
A field experiment was conducted at the Kauai Branch Station to study the long‐term effects of calcium silicate applied to a Gibbsihumox soil. The fate of applied Si was determined during 5 years of cropping at one P (280 kg/ha) and three pH levels (5.5, 6.0, and 6.5). Plant uptake by the sugarcane plant (Saccharum officinarum L.) and ratoon crops, corn, (Zea mays L.), and seven harvests of kikuyugrass (Pennesetum clandestinum H.) accounted for 12 to 21% of the applied Si. Repeated extraction of profile samples taken at the end of 5 years with 0.1N acetic acid adjusted to pH 3.5 and containing 50 ppm P recovered 14 to 28% of the applied Si. There was no evidence that applied Si moved below the 30‐cm soil depth. This indicated that 57 to 72% of the applied Si remained in the soil in some fixed form not readily displaced by phosphate solution. Water‐soluble Si and plant uptake of Si decreased as pH increased while phosphate‐extractable Si increased as pH increased.

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