| Summary: | 碩士 === 國立臺灣大學 === 園藝學研究所 === 87 === In order to reduce the irrigation run-off and contamination of the underground water, effects of different nutrient levels were investigated in Spathiphyllum "Sensation" grown in an ebb and flow system, and comparison on the growth with hand-watering was also determined. Environmental and economical concerns had generated interest in the development of substitutes to peat, under the conditions of this study, coir-based media was also used in the experiments to compare the growth responses of Spathiphyllum "Sensation" under the ebb and flow system.
Plants grew equally well from a range of 1/4 to full-strength of Johnson''s solution in the ebb and flow system, indicating the possible luxury consumption of plants was grown in the full-strength treatment, moreover, full-strength treatment produced more necrotic leaves and reduced the root growth. However, the chlorophyll content was lower in the 1/4-strength treatment and leaves showed chlorotic spots symptoms. In the full strength treatment, a high EC of 7.19mS/cm was measured in the upper portion of the medium measured at the end of the experiment, whereas for the 1/4 strength treatment, EC at the root zone was maintained at 0.79mS/cm, which was considered to be save for the plant growth. These results indicated that a range of 1/4 to half strength of Johnson''s solution was optimum for the growth of Spathiphyllum "Sensation" in the ebb and flow system.
From September, 1997 to April, 1998, there were no difference in the plant growth between irrigation methods at the same irrigation frequency, however plants grown in the ebb and flow system had the fewest number of chlorotic and puckered leaf. From May, 1998 to January, 1999, plants growth in the ebb and flow system was better than that of the hand watering treatment. In additions, the ebb and flow system could save water and nitrogen use by 33% and increased the water use efficiency by 40%.
Coirdust had a lower air-filled porosity and water holding capacity than Canadian sphagnum peat. Growing mix containing 33-60% of coirdust with perlite and treefern exhibited desirable physical properties, the pH of coirdust was desirable but EC was higher than that of peat. Na and K were tested to be 6 and 3 times higher than peat respectively, however, the P, Mg, Ca content of coirdust was less than optimum range.
No difference was observed in plant growth among various medium mixture containing either 33-50% of coirdust or 33% of peat. However, the coirdust content higher than 50% could reduce plant growth. In another experiment with medium composed of 50% of perlite and various proportions of coirdust and peat, results indicated that coirdust content up to 25% gave lower root dry weight. All these suggested that the chemical properties would affect the root growth of Spathiphyllum "Sensation".
Maximum growth was observed in 8mM-N applied in the ebb and flow system by using peat-mix as the media, while plants grown in coirdust were equally well with the ebb and flow by 4-8mM-N treatment. As a medium in the ebb and flow system, it appeared that coirdust could be a good substitute for peat. For either peat or coirdust-based medium, the optimum nitrogen requirement for Spathiphyllum "Sensation" in the ebb and flow system was 8mM. Plant dry weight decreased and necrotic symptoms occurred when nitrogen concentration exceeded 16mM in all treatments, and root dry weight decreased sharply especially in the ebb and flow treatment. Increasing nitrogen concentration paralleled increased the no of necrotic leaves, and root growth foliar N content, while K, Ca and Mg content was decreased. Due to the absence of leaching in the ebb and flow system, it was suggested to reduce the nitrogen application rates in order to maintain good quality of Spathiphyllum "Sensation".
Fertigation using once in every 3 days was shown to be optimum for peat and coirdust-mix in the ebb and flow system, while increasing the frequency to once a day was unnecessary. Coconut husk-mix had a poor water retention capacity, but the problem could be solved by increasing the fertigation frequency to once a day, suggesting that coconut husk is suitable for constantly irrigation.
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