Growth of Some Tropical Ornamental Plants on Artificial Topsoils Derived from Mixtures of Flyash, Sludge, Biochips, and Rengam Series Subsoil

Abstract

Four mixtures of artificial topsoils produced from mixing incinerator flyash, sewage sludge, biochips (from plant parts), and subsoil (from granite origin) in various proportions were used to grow some popular ornamental plants. The plants used were Bougainvillea spectabilis Ixora coccineaand three Heliconiataxa, H. psithacorum × H. spathocircinatacv. “Golden Torch,” H. rostrataand H. psithacorumcv. “Tay.” Their physiological responses to the heavy metals present in the different artificial topsoil mixtures were monitored using chlorophyll fluorescence F _v /F _m ratio, maximum photosynthetic rates and quantum yield. The overall results indicated that B. spectabiliswas the most tolerant and could grow well in all the four artificial topsoils. Ixora coccineawas the least tolerant and could only grow well in the mixtures with lesser heavy metals. The three Heliconiashad intermediate tolerance level compared with B. spectabilisand I. coccinea. Leaching test was then conducted using one of the artificial topsoils with higher flyash content to quantify the heavy metals such as cadmium (Cd), copper (Cu), chromium (Cr), iron (Fe), lead (Pb), and zinc (Zn) in the leachate under simulated heavy rainfall condition. The overall leaching test revealed that plants significantly reduced the amount of heavy metals present in the leachate. However, the amounts of Cd, Cr, Fe, and Pb present in the leachate were still higher than the control treatment, even in the presence of plants. However, the leachate Cu and Zn contents in the presence of plants were either similar to or lower than the control and, therefore, pose less environmental hazard.

Keywords:

• Artificial soil
• Heavy metal
• Ornamental plants
• Photosynthesis

Acknowledgments

This project was funded by ENV and NTU. We thank Professor Tay Choo Hwa, Dr. Lim Teik Thye, and staff of NTU Environmental Laboratory (Division of Water Resources and Transportation) for their generous loan of equipment and expertise. The staff of ENV provided materials and help and JBP provided plant materials. Professor Lam Toong Jin and Mr. Chua Whye Leng of NUS (School of Biological Sciences) assisted in N determinations.