| Summary: | 碩士 === 國立中興大學 === 土壤環境科學系所 === 99 === Phosphite (HPO3-2, Phi) is a reduced form of phosphorus, having a similar structure to phosphate (PO4-3, Pi). The former is a diprotic acid, but phosphate is a triprotic acid. Phosphite salts have been used as a fungicide for some diseases control. Some plants can used it as phosphorus fertilizer, but no phosphorus fertilizer effect for other plants, after the long-term use it even caused ecological problem. This study using hydroponic system to investigate the effect of phosphite/phosphate ratio in the nutrient solution on the growth, nitrate reductase, phosphatase, nutrient uptake of Pak-choi (Brassica chinensis L.,Cultiva). Screening Phi using bacteria from soil and inoculated into nutrient solution to evaluate their effect on the growth of Pak-choi.
Results showed that increased the phosphite/phosphate ratio in nutrient solution decreased weights of shoot and root in fresh and dry, concentrations of extractable phosphate, total phosphorus, and magnesium, activities of leaf nitrate reductase and phosphatase, and the chlorophyll index. Evidence showed phosphate contributes a partial function as phosphorus fertilizer. Although the fresh weight and dry weight of Pak-choi root of 100％ phosphate treatment was 56 %, and 67 % decreased, respectively, compared to no phosphorus treatment. The fresh weight and dry weight of Pak-choi shoot was 69 % and 9 % increased, respectively, compared to the no phosphorus treatment.
The inoculation of the top three most effective phosphate using bacteria, increased the Pak-choi shoot and root fresh weights by 37-93 % and 27-62 %, respectively, compared to no inoculation treatment
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