The effect of the flow rate of the supplied lake water and channel length on the changes in the NO3-N concentration of the solution in the channel, amount of suspended solid(SS)precipitated in the channel and yield of water spinach was investigated in the channel constructed in a lake-side greenhouse using the eutrophic Tega-lake water. It was observed that SS precipitation in the channel promoted the growth of water spinach and that the crop took up the nutrients from SS that precipitated in the channel as well as from the dissolved ions in the solution. The amount of SS that precipitated in the channel was affected by the SS amount of supplied lake water and the water flow rate. When the channel length was less than 20 m with a water flow rate of 10-20 L/min, the yield of water spinach was higher and growth was uniform from upstream to downstream in the channel. In addition, nitrogen was efficiently removed from eutrophic lake water.
We conducted indoor experiments on a local variety of water spinach in Taiwan to analyze the effect of the irradiation ratio of blue (B) to red (R) light on the morphological characteristics of stem tissue. The light spectrum was regulated by using a combination of different fluorescent lamps, and 4 different irradiation treatments were applied for the change of the energy ratio of B (450 ± 10 nm) / R (660 ± 10nm) from 2.0 to 23.9. The photosynthetic photon flux density at the top of the shoot was maintained at approximately 200 μmol m-2 s-1. Seedlings were grown for 10 days after the expansion of the cotyledon in each plot. Cross-sections of the centre of the first internode were observed microscopically; the thickness of the cortex and pith and the diameter of the stem and cavity were measured. The stem diameter increased significantly at the higher B/R ratio, while the cortex thickness did not change. The pith thickness increased significantly at the higher B/R ratio, and was positively correlated to the stem diameter (r = 0.808, P < 0.001). The increase of the pith thickness and stem diameter was associated with the increase in the cell density and number of cells in the pith with tissue. The cavity diameter was significantly small when the B/R ratio was lowest. These results indicate that a higher B/R ratio enhanced the increase of the stem diameter, pith thickness and the density and number of cells in the pith in water spinach.