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Effects of Some Fertilization Practices on Concentration of NO3--N of Pak-chio
The prime factors affect of nitrate contents of vegetables are fertiliza-
tion and nitrate reduction rate in plants. The assimilation of NO3- by plants related to the uptake of NO3-, reduction to NO2-, the conversion of NO2- to NH4+, and the incorporation of NH4+ into organic compounds. Nitrate availability, growth regulations, light, products of nitrate assimila-
tion and other physiological and environmental parameters are all factors that regulate nitrate assimilation. The nitrate reductase activity is limited by energy, which comes from photosynthates.
The first subject of this thesis was to study the effect of application of three nitrogen forms ( urea, ammonium nitrate, calcium nitrate) and spraying organic sources ( citric acid and concentrated molasses) at night to the nitrate contents of Pak-choi. The second subject was to study the effects of potassium and chloride concentrations, and with or without supplying nitrate nitrogen in nutrient at night on the growth and nitrate contents of Pak-choi.
In first study, three pot experiments, Shiow Shui soils was used. The fertilizers of total P, half of N and K were mixed into soil before seedding. The leftover N and K fertilizers were quadrisected to use at 14, 17, 20 and 23 days after planting. The organic sources used were citric acid and concentrated molasses, were used singly or mixed up as foliar fertilizers at 18, 21, 24 and 27 days after planting. In second study, two hydroponics experiments, the basic composition of nutrient solution used NCHU formula (Wu and Wang, 1995). Some treatments modifying the basic formula with concentrations of potassium (1.5, 2 times), chloride (0.5, 1.5 times), and deprivation of nitrate nitrogen to grow Pak-choi.
The results from pot experiment indicate that the application of different nitrogen forms and organic sources had no effect on yields and nitrate contents of Pak-choi grown in calcareous soil. The high concentra-
tion of organic sources would cause some leaf burn of Pak-choi leaf. The result from hydroponics experiment indicate that increasing the potassium concentration of nutrient solution will increase the yields of Pak-choi, but will not be able to decrease the nitrate contents in Pak-choi. As increasing the potassium concentration and the chloride concentration simultaneouly the nitrate contents in Pak-choi were decreased . But if only the chloride concentration increased the growth of Pak-choi were inhabited. When stop supplying of nitrate nitrogen at night did not effect the yields but decreased the nitrate contents dramatically, lowered 40 and 43 % in the two experiments. If deionized water instead of nutrient solution at night, the nitrate contents of Pak-choi were decreased 48 and 45 % for the high potassium treatments and 50 and 43 % for the high chloride treatments.|
摘 要 影響蔬菜硝酸態氮含量最主要的因子是肥料施用及植體內硝酸還原速率。硝酸態氮代謝受硝酸還原速率的限制，硝酸還原酵素活性的表現除受氮吸收量影響外，亦受光照、養分含量比例的影響，夜間硝酸態氮持續吸收，硝酸還原酵素活性變低，導致植體硝酸態氮累積，硝酸還原酵素作用需消耗能量，本研究第一部分探討：以相同肥料施用量，三種不同形態氮肥(尿素態氮、硝酸銨和硝酸鈣)及夜間噴施有機養液(味素發酵母液、檸檬酸)補充碳源，探討其對小白菜生長及植體硝酸態氮含量的影響。第二部分則以水耕試驗探討不同鉀、氯濃度以及夜間中斷供應硝酸態氮對小白菜生長及植體硝酸態氮含量之差異。 盆栽試驗採用秀水系土壤進行試驗，磷肥全量、氮鉀肥半量以基肥施用，剩餘氮、鉀肥等分四次在種植第14、17、20、23天之上午七點以灌施輔以葉面噴施方式施用，在栽植第18、21、24、27天之下午七點葉面噴施味素發酵母液、檸檬酸、二者各半和不噴施有機養液等處理，在栽種第32天採收分析。水耕試驗以吳及王1995年所提出的中興大學小白菜養液(nchu)，調整鉀(氮濃度之1.5、2倍)、氯(原液之0.5、1.5倍)濃度及夜間停止硝酸態氮供應等10個處理，栽植小白菜，定植後每七天更換養液一次，在第21天採收分析。 盆栽試驗結果，施用不同型態氮肥在試驗中，對小白菜生長未造成顯著的差異，而噴施高濃度有機養液會造成小白菜葉面受損現象，且對植體硝酸態氮並不能有效的降低，對小白菜產量及植體養分含量也無顯著性的影響。水耕試驗結果顯示在提高鉀濃度時小白菜產量會提高且差異達極顯著，而對植體硝酸態氮含量不能有效降低；降低氯濃度之養液，除植體氯含量降低外，不會影響小白菜生長及植體養分含量，而升高氯濃度之處理會使小白菜生長受阻，若提高氯濃度同時提高鉀濃度(氮的2倍)，則小白菜生長不會受阻，植體硝酸態氮含量之降低現象較僅提高鉀濃度而未提高氯濃度之處理更為顯著。夜間停止提供硝酸態氮之處理，二次試驗的結果，植體硝酸態氮在提高鉀濃度的處理降低40、43%，提高氯濃度的處理則為32、36%，差異均達極顯著(P<0.01)，此時植體氯離子濃度會有升高的趨勢，二者呈負線性相關；夜間以去離子水取代養液處理，其產量並未降低，且可有效降低植體硝酸態氮含量，在二次試驗的結果，就提高鉀濃度之處理硝酸態氮降低48、45%，提高氯濃度的處理則為50、43%，差異均達極顯著，其他離子亦同時減少。綜合水耕試驗結果小白菜水耕液在N、P、K、Cl及夜間不供應養液下，產量不降低而硝酸態氮可極顯著降低。
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