| Summary: | 碩士 === 國立臺灣大學 === 園藝學研究所 === 102 === Malabar chestnut [Pachira macrocarpa (Cham. &; Schltdl.) Walp.] (Bombacaceae) is a tropical small tree native to Mexico to central America. Growers in Taiwan usually use field soil for nursery and culture of this species. Most Malabar chestnut plants were exported and total valued 51,105 thousand U.S. dollars from 2006 to 2013. Malabar chestnut has strong growth and can be easily cultured, however, Phytophthora and Lasiodiplodia infection may cause severe lose due to stem rot and braid loss. Therefore, developing new culturing system to overtake the conventional one is expected. This study was aimed to 1) test the effect of soilless medium on growth of Malabar chestnut, 2) find the optimal nursery medium for subsequent hydroponic culture, 3) elucidate the effect of nutrient solution of hydroponic culture on growth of plants, and 4) test the feasibility of additional oxygen releasing compounds to the nutrient solution.
Malabar chestnut plants had the highest growth performance and dry mass when grown with peatmoss without other soilless medium. Plants grown with coir dust had similar appearance and dry weight compared to the peatmoss-grown. Coir dust could be a substitute for peatmoss based on eco-friendly consideration. However, coir dust did not suit for all environments and was difficult for physical and chemical adjustment. Thus, soilless mixture PVPe221 was recommended because of the plants had the best Dickson quality index (DQI) and quality index (QI) value.
Seedlings easily rotted during tap water nursery. Aerated tap water and running tap water treatments resulted in curved hypocotyls. Seedling quality was better when grown with solid medium than liquids. Seedlings grown with vermiculite (V), moss (S), and 1-P soilless mix (1-P) had similar QI value. But moss could not remove easily from root system and could increase transplanting labor cost. Malabar chestnut were recommended to nursed with V or 1-P before hydroponic culture. Under low light condition (100 μmol·m-2·s-1), plants had best performance when fertilized with Yamazaki lettuce nutrient (Y) solution, Taichung (T) solution was the second, and Hoagland solution treatment resulted in worst plant growth. Under high light condition (1,100 μmol·m-2·s-1), the best was with T solution. However, QI value was not significantly different between T solution (6.83) and Y solution (6.63). Y solution had lower chemical cost than T solution. Therefore, Y solution was recommended for hydroponic culture of Malabar chestnut.
When 0.01 g oxygen releasing compound (ORC) was added to distilled water, pH increased from 6.01 to 9.33, and pH to 10.98 when 0.02 g ORC was added. Dissolve oxygen (DO) maintained the highest during experiment period after adding ORC and pH adjustment (ORC+pH). Aerated distilled water had similar DO with ORC+pH. Distilled water without ORC or aeration had significant lower DO.
In summary, Malabar chestnut could be grown with soilless mix PVPe221 to achieve the best plant quality. Seedlings should be nursed with vermiculite or 1-P soilless mix before hydroponic culture. During hydroponic culture, Yamazaki lettuce nutrient solution was recommended both under low (100 μmol·m-2·s-1) and high (100 μmol·m-2·s-1) light conditions for better growth and lower cost. Additional oxygen releasing compounds (ORC) resulted in higher pH and dissolve oxygen (DO). ORC plus pH adjustment had the highest DO. ORC treatment could be a substitute for aeration system and had lower energy cost.
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