Plant production and water purification efficiency by rice [Oryza sativa] and umbrella plants [Cyperus alternifolius] grown in a floating culture system under various water environmental conditions
2000
Miyazaki, A. (Kyushu Univ., Fukuoka (Japan). Faculty of Agriculture) | Kubota, F. | Agata, W. | Yamamoto, Y. | Song, X.
The floating culture system was originally designed with a purpose of developing a new cropping area by growing plants on the water surface; in addition, this system can also be used as a technique for water purification by allowing plants to absorb nutrients from the eutrophied water. We investigated here the specific differences in water purification effect and plant productivity of rice and umbrella plants both of which were grown on the surface of the waters with various levels of eutrophication. The results were as follows: 1) In both species, the rate of nitrogen absorption (NR) was positively related to the crop growth rate (CGR). Both parameters greatly changed in value with water conditions, showing a negative relation with pH and positive relation with electrical conductivity (EC). 2) Application of a slow-release fertilizer as basal-dressing to rice in the eary growth stage had a beneficial effect on subsequent growth vigor, and the highest grain yield of rice was 542 g m sup(-2) comparable to the yield obtained in paddy-grown plants. The leaf photosynthetic rate, chlorophyll content and plant weight were increased, depending on the water quality, by applying acid and iron controlling chemicals together with the basal-dressing fertilizer. High pH caused an iron deficiency in rice and greatly restricted its growth. In the eutrophied waters, iron fertilizer application to plants was very effective in improving the growth. 3) CGR and water purification effect of umbrella plants were significantly superior to those of rice examined under all of the growth conditions in this study. The water purification by umbrella plants is practically expected in eutrophied water areas.
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