植物工廠水耕栽培荷蘭薄荷與澳洲薄荷之研究

Abstract

薄荷(Mentha spp., Mint)泛指唇形科(Lamiaceae)薄荷屬之草本植物，為天然香料與精油的重要原料之一。作物露天栽培受限於可耕地之面積、土壤特性及氣候變化，植物工廠水耕栽培或可解決部份問題。蔬菜硝酸鹽含量關乎食用安全，其受肥培管理及環境因子之影響。本研究探討水耕栽培荷蘭薄荷(Mentha spicata)及澳洲薄荷(Mentha australis)之適當養液配方、栽培密度、光質、溫度及降低硝酸鹽含量的方法，期能於植物工廠穩定量產清潔、硝酸鹽含量低於2000 ppm之兩種薄荷。2011年7月4日至7月26日(期間溫度27.0~28.8℃)，在國立臺灣大學農業試驗場園藝分場溫室內分別種植兩種薄荷，栽培密度為每箱(43×36 cm2) 12株，施用山崎、臺中農業改良場家庭葉菜、Hoagland及Thailand養液，採收前三天將養液換為清水，四種養液之單株葉鮮重間皆無差異(荷蘭薄荷與澳洲薄荷分別為5.03~6.02及6.38~7.83 g，以下數據同此順序)；荷蘭薄荷葉片10種元素含量皆在適宜範圍內，但澳洲薄荷以臺中農改場家庭葉菜養液栽培之葉片鉬含量僅0.15μm•g-1 DW，並表現病徵；而Hoagland養液栽培之葉片硝酸鹽含量最低(741及906 ppm)，且生物活性成分齊墩果酸含量較高。繼於2011年8月11日至9月1日(26.8~28.3℃)分別種植兩種薄荷，以Hoagland養液栽培並於採收前三天換為清水者，其單株葉鮮重未下降(6.87g及6.13 g)，且葉片硝酸鹽含量顯著較低(506及1434 ppm)、Zn含量較高；但以山崎養液栽培者，採收前三天換清水顯著降低單株葉鮮重。故於2011年9月15至10月6日(24.5~27.8℃)以Hoagland養液定植兩種薄荷，採收前一天換清水顯著降低葉片硝酸鹽含量(1680及1990 ppm)，且單株葉鮮重(4.81 g及4.50 g)與採收前二、三天及未換清水者無差異，亦不影響澳洲薄荷葉片10種元素含量。2011年10月5日至11月17日(21.0~24.2℃)在園藝分場溫室分別種植兩種薄荷，每週連續採收共收四次，每次採收之莖葉立即照光2、3及4小時皆不影響葉片10種元素、有效成分齊墩果酸及熊果酸之含量，但其降低葉片硝酸鹽含量之效果皆不及採收前一天換清水。2011年11月24至12月15日(16.5~22.5℃)於園藝分場溫室分別種植兩種薄荷，每箱種18與12株之單株葉鮮重皆比6株者顯著較低，但種植18株之單位面積總產量(324.81及376.07 g/m2)顯著較高；而栽培密度對硝酸鹽含量並無影響。故以每栽培箱種植18株進行下列試驗。2012年3月9日至3月29日在臺大人工氣候室分別種植兩種薄荷，於五種日夜溫35/30℃、30/25℃、25/20℃、20/15℃及15/13℃栽培，在25/20℃下生長之單株葉鮮重顯著較高(5.67 g及7.03 g)、硝酸鹽含量顯著較低(538及572 ppm)，且荷蘭薄荷之齊墩果酸含量與澳洲薄荷之熊果酸含量亦較高。另於人候室之LED植物栽培室26℃與16/8 hr光週下，以八種不同光質及光強度分別栽培兩種薄荷，其中以115 μmol•m-2s-1之混和紅藍綠發光二極體為光源者，其單株葉鮮重(4.37 g及7.02 g)、分枝數、葉片數、根長與根乾重皆較高，且硝酸鹽含量較低(2499及4223 ppm)。於臺大完全控制型植物工廠25/20℃、但高相對濕度RH 95%逆境下，以100 μmol•m-2s-1之六種不同光質比例的發光二極體栽培兩種薄荷，以7R2B為光源者其單株葉鮮重顯著較高(1.75 g及1.82 g)，硝酸鹽含量(1776及2257 ppm)顯著較低；澳洲薄荷之齊墩果酸及熊果酸含量亦較高。2012年2月6日至3月19日(16.0~25.2℃)在太陽光型植物工廠、及於22/20℃以300 μmol•m-2s-1 T5燈為光源之完全控制型植物工廠內，分別種植兩種薄荷。於完全控制型植物工廠連續4週採收之單株總產量(10.96及15.86 g)皆高於太陽光型者(8.73及8.52 g)，硝酸鹽含量亦低於2000 ppm。於兩型植物工廠栽培荷蘭薄荷之葉片Mo含量、齊墩果酸與精油中檸檬烯含量，皆較唐山園藝及city’super所售者高，香芹酮含量較低，而葉片K、P、Mg、Zn及Cu含量亦較唐山園藝所售者高；兩型植物工廠栽培澳洲薄荷之葉片Ca、K、P、齊墩果酸、熊果酸與精油中檸檬烯及香芹酮含量皆較唐山園藝所售者高。故在完全控制型植物工廠於日夜溫25/20℃、300 μmol•m-2s-1 T5燈為光源，或於20~25℃季節在太陽光型植物工廠，採用Hoagland養液，並於採收前一天換清水，可每週穩定量產清潔、低硝酸鹽含量之荷蘭薄荷及澳洲薄荷。

Mints (Mentha spp.) were generally referred to the herbs in the Mentha of Lamiaceae. Mint is one of the important raw materials of natural aromatizer and the essential oil. Field production of crops is limited by the area and soil properties of the arable land and climate change. Hydroponics in the plant factory may solve part of this problem. The nitrate content of leafy vegetable is related to the food safety and affected by nitrogen fertilizer and environments. This research aimed to study the appropriate nutrient solution, planting density, light quality, temperature and nitrate content reducing method of hydroponically grown Mentha spicata and M. australis in order to stably mass-produce clean mint with nitrate content less than 2000 ppm in the plant factory. Two mints were grown hydroponically with 12 plants in one container (43 × 36 cm2) in the greenhouse of The Experimental Farm, College of Bioresourcces and Agricculture, National Taiwan University during July 4 through July 26, 2011 (27.0~28.8℃). Nutrient solutions of Yamazaki, Taichung District Agricultural Research and Extension Station (TDARES) for leafy vegetables, Hoagland and Thailand were applied. For leaf fresh weight (F.W.) per plant, non-significant difference existed among four nutrient solutions by water replacement on 3 days before harvest (Mentha spicata and M. australis were 5.03~6.02 and 6.38~7.83 g, respectively. The following data were shown with by order). Contents of ten elements in leaves of M. spicata were in the appropriate range. But leaf Mo content was only 0.15 μm•g-1 DW and symptoms shown in leaves of M. australis grown with TDARES leafy vegetable solution. The lowest nitrate content (741 and 906 ppm) and the highest bioactive ingredients of oleanolic acid contents were exhibited when two mints were applied with Hoagland nutrient solution. During August 11 to September 1, 2011 (26.8~28.3℃), water replacement of Hoagland nutrient solution on 3 days before harvest did not reduce leaf F.W. per plant (6.87g and 6.13 g) of two mints, and the leaf nitrate content was also significant lower (506 and 1434 ppm) andbZn content higher. But leaf F.W. per plant was reduced by water replacement on 3 days before harvest with Yamazaki nutrient solution. During September 15 through October 6, 2011 (24.5~27.8℃), two mints were grown with Hoagland nutrient solution. Water replacement on 1 day before harvest significantly lower nitrate content (1680 and 1990 ppm). Concerning leaf F.W. per plant (4.81 g and 4.50 g), non-significant difference was showed among water replacement on 1, 2, and 3 days before harvest and no replacement. Non-significant difference on contents of 10 elements existed among four treatments in leaves of M. australis. Two mints were grown in the greenhouse during October 5 through November 17, 2011 (21.0~24.2℃), and weekly-heavested for four times. Harvested shoots were immediately illuminated for 2, 3 and 4 hours. No singnificant effect on contents of 10 elements, oleanolic acid and ursolic acid in leaves of two mints. But reducing effects on nitrate content by illumination were less than water replacement. During November 24 through December 15, 2011 (16.5~22.5℃), the leaf F.W. per plant with 18 or 12 plants per container were lower than 6 plants, but density of 18 plants were showed significantly higher yield (324.81 and 376.07 g/m2) in the greenhouse. Planting density did not affect the leaf nitrate content. Therefore, 18 plants per container were applied in the following experiments. Two mints were grown under day/night temperature 35/30℃, 30/25℃, 25/20℃, 20/15℃ and 15/13℃ in the Phytotron of NTU from March 9 through March 29, 2012. At 25/20°C, higher leaf F.W. per plant (5.67 g and 7.03 g), lower nitrate content (538 and 572 ppm), higher oleanolic acid contents in M. spicata and higher ursolic acid contents in M. australis were showed. Two mints were then grown with eight trratments of different light quality and intensity under 26℃ and 16/8 hr photoperiod. Significantly higher leaf F.W. per plant (4.37 g and 7.02 g), branch number, leaf number, root length and root dry weight, but significantly lower nitrate content were exhibited in two mints grown with red, blue and green light-emitting diode (LED) of 115 μmol•m-2s-1light intensity. Under 95% relative humidity stress at 25/20℃, two mints were grown with six kind of LED with mixed light quality and 100 μmolm-2s-1 light intensity in the closed type plant factory of NTU. Significantly higher leaf F.W. per plant (1.75 g and 1.82 g), and significantly lower nitrate content (1775.93 ppm and 2256.60 ppm) were shown in 7R2B LED treatment in two mints, and significant higher oleanolic acid and ursolic acid contents in M. australis. Two mints were cuttivated in semi-closed type plant factory and closed type plant factory with 300 μmolm-2s-1 light intensity and T5 lamp at 22/20℃ during February 6 through March 19, 2012 (16.0~25.2℃). Continuous weekly harvest for four times in closed type plant factory showed higher yield per plant (10.96 g and 15.86 g) with nitrate content lower than 2,000 ppm than in the semi-closed type plant factory. M. spicata grown in two types of plant factory showed higher contents of Mo, and oleanolic acid in leaf and limonene in essential oil than commercial products of ‘Tangshan’ and ‘city'super’; but lower carvone content in essential oil, higher leaf K, P, Mg, Zn and Cu contents than in ‘Tangshan’ product. M. australis grown in two types of plant factory showed higher contents of Ca, K, P, oleanolic acid, ursolic acidin leaf, and limonene and carvon in eessential oils than ‘Tangshan’ products. Therefore, in closed type plant factory with 25/20℃ and 300 μmolm-2s-1 of T5 lamp, or in semi-closed type plant factory in seasons of 20~25℃, producing clean M. spicata and M. australis with nitrate contents lower than 2000 ppm may be achieved with application of Hoagland nutrient solution and water replacement on 1 day before harvest.