不同比例硝酸態與銨態氮之水耕液對葉菾菜及紫色葉用甘藷生長與養分吸收之影響

水耕栽培於不使用介質作為養分緩衝平衡的條件下，水耕液中酸鹼度 (pH) 和電導度 (EC) 的恆定與水耕液配方有直接且重要的關係。本試驗之目的在探討不同比例硝酸態氮與銨態氮之水耕液對菾菜及紫色葉用甘藷生長與養分吸收的影響。本試驗選擇硝酸態氮與銨態氮比例 (硝銨比) 為五比一和七比一，兩種不同氮源比例栽培菾菜和紫色葉用甘藷，連續使用水耕液四個月， pH 設定為6.0，電導度為1.8 dS m-1。試驗開始後，每五天補充水耕液體積為12 L 後，調整 pH 和電導度。菾菜連續栽培120天，每20-25天採收一次，共六次；甘藷葉連續栽培140天，每30-50天採收一次，共四次。結果顯示，硝銨比為七比一處理菾菜的水耕液電導度下降較快，養分利用快；兩種銷銨比處理菾菜的水耕液中各種元素明顯下降，除了鈣和鋅出現累積的現象。兩種硝銨比處理的菾菜中總氮、磷、鉀、鎂、鐵、錳、銅、鋅的濃度沒有差異，菾菜中硝酸鹽的 (nitrate) 濃度於前五次採收約為1,900-3,900 mg kg-1 (鮮重基準)；鈣濃度於硝銨比為七比一處理的水耕液中顯著較高。硝銨比為七比一的水耕液中總可溶性糖濃度較高；總游離胺基酸態氮於硝銨比處理為五比一的水耕液中較高。隨試驗開始到試驗結束，可溶性碳於兩種硝銨比處理的水耕液中沒有差異，但有逐漸累積的情形。硝銨比為七比一或五比一處理紫色葉用甘藷的水耕液中，從試驗開始後30天，當電導度降為1.4 dS m-1，兩種硝銨比的水耕液 pH 皆下降為4.2，因為紫色葉用甘藷吸收過多銨態氮和錳；水耕液中各種元素明顯下降，但鎂出現累積的現象。兩種硝銨比處理的紫色葉用甘藷中總氮、磷、鉀、鈣、鎂、鐵、錳、銅、鋅的濃度沒有差異；硝酸態氮的濃度為 2,100-2,600 mg kg-1 (鮮重基準) 。試驗開始後兩種硝銨比處理的水耕液總可溶性糖、可溶性碳和總游離胺基酸態氮沒有差異。總可溶性糖和總游離胺基酸態氮有逐漸下降的趨勢，可溶性碳有逐漸累積的現象。水耕蔬菜栽培，可以不換水耕液的方式管理，定期加入因蒸散而損失的水，當電導度下降為所設定的定值時，再添加養分使其達到起始濃度，可以維持蔬菜之正常生長。依菾菜的吸收特性，本試驗中可提高兩種硝銨比補充養液中銨態氮、硝酸態氮、鉀、鎂和錳的濃度，降低鈣和鋅的濃度，來維持水耕液中養分的平衡。本試驗硝銨比為五比一的水耕液適合生產菾菜，可以提高水的利用效率，以維持水耕液中酸鹼度和電導度的變化。依甘藷葉的吸收特性，本試驗中可提高兩種硝銨比補充養液中的銨態氮、硝酸態氮、鉀和錳的濃度，降低鈣、鎂的濃度，以維持水耕液中養分的平衡。本試驗硝銨比為七比一的水耕液適合用做生產紫色葉用甘藷，可維持水耕液中酸鹼度和電導度的變化。

關鍵字

pH ；電導度；總可溶性糖；可溶性碳；總游離胺基酸態氮

並列摘要

Hydroponics include all methods of soilless culture and supply plants with nutrient solution for growing. It’s important that hydroponic solution on keeping constant pH and electric conductivity (EC). Hydroponic solution recipes play an important role on this respect. It has been known that varying concentrations of NO3--N and NH4+-N in nutrient solutions affect the pH change significant. The purpose of this study was to study the changes of nutrient solutions with two NO3--N : NH4+-N ratios under cultivation of swiss chard (Beta vulgaris) and purple leaves sweet potato (Ipomoea batatas). The cultivation period lasted for four month. The two kinds of NO3--N : NH4+-N were 7 : 1and 5 : 1. The initial pH and electric conductivity (EC) was set at pH 6.0 and 1.8 dS m-1, respectively. There was four replicates for each treatment and arranged in a ramdomized complete block design. The solutions were adjusted to their initial volume (12 L) every five days. The EC of solutions were adjusted to initial volume (1.8 dS m-1) when the EC was lower than 1.4 dS m-1. The composition of solutions were measured after each EC and pH adjustments. The plants were sampled every 30 days. The concentration of N, P, K, Ca, Mg, Mn, Fe, Cu and Zn of plant samples and hydroponic solution were measured. The soluble sugar, soluble carbon, soluble amino acids and total bacterial counts were measure every month. The results showed that pH of the two solution were maintained at 4.8 to 6.2 during the cultivation period Swiss chard prefered 7 : 1 nitrate-ammonium ratio solution to 5 : 1 ratio solution. Most of nutrients of the hydroponic solutions decreased during cultivation, in contrast, calcium and zinc accumulated. There were no difference in concentrations of macro- and micro-nutrients in plants of Swiss chard cultivation in two hydroponic solutions. The nitrate concentrations in swiss chard were 1,900-3,900 mg kg-1 (FW) in first to fifith harvests. There were no difference in soluble carbon in the two nutrient solutions during the cultivation period. The total soluble sugars and free amino acids were significant higher in NO3--N : NH4+-N (7 : 1) solution than NO3--N : NH4+-N (5 : 1) solution after 60 days of treatment. The pH of hydroponic solutions of the two NO3- -NH4+ ratios of purple leafy sweet potato dropped to 4.2 after 30 days of treatment, and then maintained at 4.8 to 6.4 till the end of experiment. The concentrations of most nutrients the two hydroponic solutions decreased during cultivation period, in contract, magnesium accumulated. There were no difference in macro- and micro-nutrients concentration in purple leaf sweet potato cultivated in the two hydroponic colutions. The nitrate concentrations of purple leafy sweet potato were 2,100-2,600 mg kg-1 (FW) in first to fourth harvests.There were no differences in concentration of soluble carbon, total soluble sugars and total amino acids in the two solutions during cultivation period.