小白菜品種硝酸鹽含量差異之研究

Research on Difference of Nitrate Content among Cultivars of Chinese Mustard (Brassica campestris L. ssp. chinensis (L.))

陳坤峯(Kung-Feng Chen)

指導教授 ： 楊雯如

共同指導教授 ： 羅筱鳳 ； 林宗賢(Tzong-Shyan Lin)

國立臺灣大學/生物資源暨農學院/園藝學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.02303

摘要

小白菜(Brassica campestris L. ssp. chinensis (L.))為台灣重要短期栽培作物，在高氮肥與光強度不足下栽培容易累積硝酸鹽，品種間累積能力可能有差異。本研究先以13個小白菜品種為材料，在夏季施以推薦施肥量，氮素(N)120 kg•ha-1磷酐(P2O5)90 kg•ha-1氧化鉀(K2O)120 kg•ha-1栽培，研究硝酸鹽累積的差異性。夏作選出之四品種，作為冬作及春作之材料，施以不同氮肥量栽培對小白菜品種硝酸鹽累積的影響。本試驗預期了解品種、氮肥量及栽培季節三因子對小白菜硝酸鹽累積之關係。
在夏季，所有品種硝酸鹽累積含量有差異，但除B317品系外，其餘皆未超過歐盟春夏季萵苣標準含量2500 mg•kg-1。在冬季栽培4個小白菜品種，全株硝酸鹽含量在建議施肥量下已高過歐盟秋冬季萵苣標準含量4500 mg•kg-1，施肥量增加時，鮮重未顯著提高，但是硝酸鹽含量顯著增加。春季試驗結果與冬季相似。
低光及低溫環境下，小白菜光合作用速率與氮同化作用能力皆下降，導致葉身累積未同化的硝酸鹽；硝酸鹽而運至葉柄儲藏的量也隨葉身累積量增加而增加。葉柄基於占全株比例約30%-80%以及其硝酸鹽含量為葉身之1.5-2倍。因此，冬季葉柄硝酸鹽累積量高時，品種間葉身含量差異無法於全株含量差異顯現出來。
依生產低硝酸鹽含量蔬菜為考量，在不同季節應有不同的推薦施肥量。在光度不足及溫度低的環境下，由於施以120 kg•ha-1 N氮肥量栽培時所有品種雖然具有最大的鮮種，但是含量皆超過標準；施以60 kg•ha-1 N氮肥量則植株鮮重不足，所以氮肥量應該介於60-120 kg•ha-1 N之間。
品種篩選方面，無法藉由外形進行篩選，而應該以葉身同化能力輔以葉柄累積量及占全株比例作為考量。此外，冬季品種間生長速率與全株含量達顯著負相關性可能可作為冬季品種篩選指標。

關鍵字

小白菜 ； 品種 ； 氮肥量 ； 季節 ； 硝酸鹽累積 ； 葉柄 ； 篩選 ； 光合作用

並列摘要

Chinese mustard (Brassica campestris L. ssp. chinensis (L.)), an important leafy vegetable in Taiwan, often accumulates nitrate when nitrogen fertilizer is over applied especially under low light intensity. The accumulation may be different among cultivars. In the present study, 13 Chinese mustard cultivars were first evaluated their difference in nitrate accumulation in summer. The amount of nitrogen fertilizer was applied according to the suggested guideline (N:120 kg•ha-1; P2O5:90 kg•ha-1, K2O:120 kg•ha-1). The 4 selected cultivars were used to study the effect of nitrogen fertilizer on seasonal nitrate accumulation in winter and spring. The relationship among cultivars, amount of nitrogen fertilizer, and seasonal effect in Chinese mustard for nitrate accumulation were studied.

In summer, nitrate content of whole plant in all the lines tested were significantly different and did not over accumulate (< 2500 mg∙kg-1) except B317. In winter, The nitrate content of the whole plant of 4 selected lines was higher than 4500 mg•kg-1 when the N fertilizer was same as what applied in summer. The fresh weight of 4 selected lines was not increased as N fertilizer increased, but nitrate content of whole plant was significantly increased. In spring, the similar result was obtained.

Under low light intensity and low temperature conditions, the photosynthetic rate and nitrogen assimilation capability in the leaf blade of Chinese mustard decreased, which resulted in unassimilated nitrate accumulated in leaf blade. The transport of nitrate to petiole was increased as the nitrate accumulated in leaf blade increased. In Chinese mustard, petiole accounts for 30%-80% of whole plant in weight, and the nitrate content in petiole was 1.5 to 2 folds than in leaf blade. Thus, the nitrate content in petiole might overwrite the difference in leaf blade among cultivars in winter.

For producing low nitrate content vegetables, it ought to have different fertilizing guidelines for different seasons. Under low light intensity and low temperature conditions, the nitrate content of the 4 selected lines exceeded 4500 mg•kg-1 when 120 kg•ha-1 N fertilizer was applied, whereas the nitrate content of which was under 4500 mg•kg-1 when 60 kg•ha-1 N fertilizer was applied. However, the fresh weight was traded off. Thus, the amount of N fertilizer should be between 120 and 60 kg•ha-1.

For screening low nitrate content cultivars, the assimilation capability of leaf blade and the ratio of petiole in whole plant should be considered at the same time. A negative correlation between growth rate and whole plant nitrate content might be a breeding index especially for winter cultivars.

並列關鍵字

Chinese mustard ； cultivar ； nitrogen application rate ； season ； nitrate accumulation ； petiole ； screening ； photosynthesis

參考文獻

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