Characteristics of nutrient absorption and water purification in some plant species grown by floating culture system

Abstract

Nutrient absorption and water purification by rice (Oryza sativa L.), canna (Canna indica L.), reed (Phragmites communis Trin.), and umbrella plant (Cyperus alternifolius L.), grown by the floating culture system, were compared under different pH conditions in natural water. The pH of the rooting zone in natural water changed due to the increase in the CO₂ concentration associated with root respiration, which was achieved by placing the roots in a plastic pot attached beneath the float to isolate the roots from the outside water. The absorption of nutrients (N and P) by umbrella plants was higher than that by the other plant species and was not inhibited by high pH values. In addition, the absorption of nutrients (N, P, K, and Fe) by umbrella plants increased with the application of a slow-release fertilizer to the basal part of the roots. As a result, umbrella plants grown with fertilizer displayed a strong water purification effect, regardless of the pH values. On the other hand, nutrient absorption by rice was severely inhibited by high pH values when fertilizer was applied. This was because the absorption of Nand P increased with fertilizer application, while the absorption of Fe by rice was markedly reduced under high pH conditions, resulting in iron deficiency. Therefore, we suggest that species tolerant to high pH conditions, such as umbrella plants, should be selected and that fertilizer should be applied to those plants, although the levels of the nutrients contained in the fertilizer should not exceed those corresponding to the absorption capacity of the plant, for improving water quality in closed natural water bodies with high pH values

Key Words:

• fertilizer application
• floating culture
• nutrient absorption
• pH
• water purification