| Summary: | 碩士 === 國立中興大學 === 園藝學系所 === 94 === The objectives of this study were to evaluate the effects of applying NH4Cl at concentration of 0, 50, 100 and 200 ppm on the growth and nitrate contents in two leafy vegetables, lettuce ‘Hsing Nong No.1’ and pak-choi ‘San Feng’, hydroponicly cultured in Hoagland solution.
Results indicated that supplement of NH4Cl in Hoagland solution had significant effects on increasing NH4+ contents, glutamine synthetase activity and total protein contents in both lettuce and pak-choi leaves. Chlorophyll contents and photosynthetic rates were found also increased, and consequently, the plants with NH4Cl supplement showed significant increases in plant height, leaf area and other horticultural characteristics as compared to the control.
Supplement of NH4Cl to hydroponic solution showed quadratic effects on the decrease of NO3- contents in the leaves of both vegetables. The most effective concentration of NH4Cl were found at 50 ppm on lettuce and at 100 ppm on pak-choi, and the NO3- contents were 20.7% and 16.8% lower than the control, respectively. The trends of the decrease in NO3- in both vegetables were found similar in winter season and in summer season. Further experiments showed that the presence of Cl- in the solution was possibly the main reason that caused the reduction in NO3- concentration. It is postulated that the anion competition between Cl- and NO3- inhibited the absorption of NO3- and subsequently decreased the NO3- contents in the leaves of both lettuce and pak-choi. The decrease of NRA activity as observed in this study may due to the decrease in NO3- because NRA is a substrates activate enzyme.
In conclusion, the supplement of NH4Cl at 50 ppm or at 100 ppm to hydroponic solution had dramatic effects not only on the decrease of nitrate contents in lettuce and in pak-choi but also on the increase of growth and yield. It is worthy of further study for the commercial production of vegetables of high yield and safety.
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