利用插入式水分電導度量測儀建立蝴蝶蘭栽培水苔肥培管理模式

Establishing Fertilization Model of Sphagnum Moss by Plug-in Water-EC Meter in Phalaenopsis Cultivation

孫維揚(Wei-Yang Sun)

指導教授 ： 張耀乾

國立臺灣大學/生物資源暨農學院/園藝暨景觀學系/碩士(2021年)

https://doi.org/10.6342/NTU202103064

摘要

臺灣蝴蝶蘭 (Phalaenopsis spp.) 栽培目前常以插入式水分電導度儀測量介質狀態，而依循之介質溶液電導度 (pore water electrical conductivity, ECp) 建議值，係由Pour- through法 (PT法) 建立。PT法測值為介質 VWC (volumetric water content, VWC, θ) 於容器容水量 (container capacity) 下測得；插入式量測儀則能在不同 VWC下進行測量。然而 ECp會因介質 VWC下降而上升，無法與 PT法之建議值對照。且臺灣業者常以水苔栽種蝴蝶蘭，其理化性質與土壤差異極大，使用插入式量測儀進行監測之可行性尚須確立。
本研究使用之 Delta- T WET sensor，探討水苔 VWC、ECp與總鹽類含量之關係。水苔 ECp值與 VWC之變化關係為三次曲線，當水苔 VWC逐漸下降時，ECp測值會逐漸上升，且變化關係不受試驗中不同肥料 EC值 (0至 1.6 dS∙m-1)、肥料配方、乾燥循環所影響。故研究以容水量時測得之 ECp值定義為 ECp (θ= container capacity) (ECp (θ= cc))，可表示水苔內鹽類含量相同時，受 VWC下降而上升之 ECp值，即可與 PT法測值對應。並使用 VWC- ECp- ECp (θ= cc)關係建立之迴歸模型，將不同 VWC下測得之 ECp轉換成可統一比較之 ECp (θ= cc)以利量測結果之判讀。
水苔 ECp (θ= cc)可以做為判定水苔肥料管理之標準，故施用不同 EC值追肥後調查水苔 ECp (θ= cc)上升幅度，提供業者施肥時建議。澆灌不同濃度追肥之後，水苔 ECp (θ= cc)隨施用肥料濃度線性上升，不受原本水苔內鹽類含量影響。依照 ECp (θ= cc)施用追肥後的上升變化，得出澆灌 1 dS∙m-1液肥並使水苔增加 0.01 m3∙m-3 VWC時，水苔 ECp (θ= cc)會增加 0.018 dS∙m-1。業者可於施肥前計算預計增加之 VWC與 ECp (θ= cc)，即可計算出肥料濃度建議值。
水苔在復水後，因為遲滯現象需等待平衡，且平衡期間測值不精準。故試驗目的為觀察要排除遲滯現象影響測值所需等待之平衡時間。當水苔復水後 VWC越低，平衡期間 ECp值的變化越大，且平衡後的 ECp值與初期乾燥過程的測值差距越大，提高復水程度則可減少 ECp值復水前後差異。遲滯現象對水苔 VWC變化影響皆小於 0.041 m3∙m-3，可以被忽略，而復水至 0.4 m3∙m-3以上，平衡 2至 3天後與平衡最後一天的 ECp測值誤差低於 0.1 dS∙m-1。考量監測時效，建議澆灌液肥 1至 3天後以 WET sensor監測水苔 ECp。
以上述結果建立之模型，計算建議施肥濃度，在蝴蝶蘭植株上進行四次施肥之澆灌，共經過 5個月的栽培過程，在修正 VWC於澆灌後的上升幅度後，即可使建議的施肥達到目標的水苔養分狀態 (ECp (θ= cc))。利用模型與 ECp (θ= cc)疊加公式計算施用的肥料 EC值，能達到目標水苔鹽類含量 ( ECp (θ= cc) 值 1.0 dS∙m-1)。顯示精準得知施肥後水苔 VWC上升幅度，便可利用 ECp (θ= cc)計算模型與 ECp (θ= cc)施肥後上升公式，計算施用的肥料 EC值，使栽培蝴蝶蘭時澆灌適當 EC值液肥，水苔鹽類含量達到目標區間。
綜合試驗結果，以 WET量測儀監測水苔可精準呈現 VWC與 ECp值變化關係，並以此建立 VWC- ECp- ECp (θ= cc)迴歸模型，能計算出水苔 ECp (θ= cc)值，協助業者參照 PT法肥培建議判斷水苔養分狀態。ECp (θ= cc)計算模型搭配 ECp (θ= cc)施肥後上升公式，可協助計算施肥的 EC值濃度以達到預計的水苔鹽類含量。澆灌後 1至 3天後檢測澆灌EC並修正施肥操作，有利於蝴蝶蘭栽培時精準控肥。

關鍵字

蝴蝶蘭 ； 介質溶液電導度 ； 介質含水量 ； WET量測儀 ； 水苔

並列摘要

The suggestions for phalaenopsis fertilization have been well researched, but the mothod for monitoring media nutrients, Pour-through (PT method), is applicable only when the container capacity of medium is reached. The Delta-T WET sensor, a plug-in water content and electrical conductivity meter, has been used to measure medium water content and pore water electrical conductivity (ECp) in industries in Taiwan, since it can measure the values when water content does not reach container capacity. However, ECp is is affected by the changes of the medium water content, so that it cannot be compared directly with the suggestions established by the PT method. In addition, the growers in Taiwan often use sphagnum moss for phalaenopsis cultivation, the physical properties of sphagnum moss are quite different from those of soil. As a result, parameter calibrations of using the WET sensor for phalaenopsis cultivation needs to be investigated.
The experiment explored the relationship among the water content, ECp and the total salt content of the sphagnum moss with WET sensor. The ECp and water content exhibited a cubic curve relationship, which was not affected by the EC of fertilizer (0 to 1.6 dS∙m-1), fertilizer formula, and drying cycles during the experiment. The ECp (θ= container capacity) value (ECp (θ= cc)) was established to represent the ECp value when sphagnum moss was at container capacity, so that it represented total soluble inorganic salt content of sphagnum moss without the effect of the water content or ECp, and it can be directly compared with the recommendations established by the PT method.
After setting up the basis of ECp (θ= cc), the experiment investigated the superposition of ECp (θ= cc) of sphagnum moss after fertilizing with different EC fertilizers. The relationship between the ECp and the water content of sphagnum moss was not affected by the EC of fertilizer, and the increasing trend of ECp (θ= cc) in the sphagnum moss after fertilization was not affected by the fertilizer EC value. If 1 dS∙m-1 liquid fertilizer was used to increase 0.01 m3∙m-3 water content of sphagnum moss, the ECp (θ= cc) would increase by 0.018 dS∙m-1.
The hysteresis was observed during the process of rehydration in the sphagnum moss, which affected the accuracy of measurement. Therefore, the experiment investigated the time to eliminate the effect of hysteresis. If the water content of the sphagnum moss after rehydration was low, the ECp measured would change greatly during the equilibrium period, and the ECp after the equilibrium period had a large difference from the value measured during the first drying process, so it could make the physical properties of sphagnum moss remain similar with the higher degree of rehydration. The effect of hysteresis on the water content of sphagnum moss could be ignored. The ECp difference between media equilibrated for 2 to 3 days and fully equilibrated would be within 0.1 dS∙m-1 after the sphagnum moss was rehydrated to more than 0.4 m3∙m-3. Considering the rapid need of operation in the industry, it is recommended to measure the ECp of sphagnum moss with a WET sensor 1 to 3 days after fertigation.
After the three-dimensional model among ECp (θ= cc), ECp and water content was established, the model and the ECp (θ= cc) calculation equation were used to calculate to the EC value of the fertilizer during five times of drying process and four times of fertilization in phalaenopsis cultivation. The ideal total salt content in sphagnum moss was reached (target ECp (θ= cc) as 1.0 dS∙m-1). It was demonstrated that if the change in water content of sphagnum moss was known, the ECp (θ= cc) model could be used to calculate appropriate EC fertilizer to reach the expected total salt content range of sphagnum moss in phalaenopsis cultivation.
Based on the results, WET sensor can accurately monitor the water content and ECp of sphagnum moss. Using the established ECp (θ= cc) calculation model combined with the ECp (θ= cc) change equation, the growers can judge the total salt content of the sphagnum moss and refer to the recommendations built by the PT method. They can also calculate the fertilizer EC to reach the expected salt content of sphagnum moss, with monitoring the ECp (θ= cc) of sphagnum moss 1 to 3 days after fertigation and use the results to modify fertilizaion operation. By this way, the growers can accurately control the fertilization for phalaenopsis cultivation.

並列關鍵字

Phalaenopsis ； pore water electrical conductivity ； medium water content ； WET sensor ； sphagnum moss

參考文獻

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