Trials on reducing nitrate content in leafy vegetables by means of horticultural measures

• Main Authors: Lin, Shu-fei, 林淑妃
• Other Authors: Cheng-Yung Cheng
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/73416940541248206978

碩士 === 國立臺灣大學 === 園藝學系研究所 === 86 === High nitrate content in the foodstuff has been proven to be hazardous to t he human health. Among the horticultural crops, leafy vegetables tend to accum ulate high nitrate content in the tissues. Experiments have been con-ducted to produce vegetables of both reasonable yield and high quality, i.e.low nitrate , high vitamin C and high mineral contents. The growth medium prepared from c ultivated soil mixed with 5-20% v/v bark compost contained 8.7-13.4% organic matter has been used in the experiments. On 5th (when Pak-choi seeds germinati on rate exceeds 90%)and 20th day after sowing, each 31.11kg N/ha in urea form was applied to the soil. Pak-choi har-vested on 30th day contained less than 1 000mg/kg f.w.of nitrate.Those har-vested between 35-40th days contained less t han 500mg/kg f.w., while vitamin C content in all samples exceeded 1000mg/kg f .w.. Pak-choi grown in a medium containing 12.4-13.4%organic matter and harve sted on 30th day after sowing resulted in a plant weight of 20 gram up and a n itratecontent of less than 550 mg/kg f.w.. The result seems to be an ideal way of production. The analyses of Pak-choi depicted that the nitrate content in outer leaveswas significantly higher than those of inner leaves, while this tendency couldnot be observed in leaf lettuce. The average nitrate content ra nged around 1000mg/kg f.w. and vitamin C 1600mg/kg f.w.in middle leaves. In g arland chrysanthemum , an increased rate of nitrogen application corre-lated p ositively with an increase in nitrate concentration. An application of187.65kg N/ha in the treatment resulted in as much as nitrate content 4000mg/kgf.w.. D rought treatment of the medium resulted in a high nitrate content in Pak-chei leaves when harvested in the early morning. 40 day-old Pak-choi derooted, ba re rooted or with intact roots and attached soil could be cold stored at 21℃ up to 21 days. The former 2 treatments leadto a nitrate content less than 250 mg/kg f.w. and vitamin C content higher than1200 mg/kg f.w. in the leaves, whi le the latter (bare rooted ones) resulted inan inferior quality. Cold storag e of lettuce seemed not to change much both in nitrate and vitaminC contents, while an acropetal transport of N and K seemed to occur from rootsto shoots du ring storage.