| 摘要: | 過去，農民灌溉時，僅藉由以往的經驗進行操作，或是依據土壤水分的測定、蒸發散量的估算、對植物直接測量其莖水勢、氣孔導度等，以決定是否灌溉。這些方法的使用上多半較為繁瑣，或對植物、土壤具破壞性，並且僅能反映出一小區域的狀況，本文利用作物水分逆境指數(Crop Water Stress Index, CWSI)來對玉米進行監測，量化作物的水分狀況。欲透過 CWSI 對作物進行監測，首先需經由實驗建立北台灣玉米之上下基準線，??為葉片溫度；??為空氣溫度，下基準線(?? ? ??)?為植物以潛在蒸發散量行蒸散時的葉溫與氣溫之差值；(?? ? ??)?上基準線，為植物無法行蒸散時的葉溫與氣溫之差值。經過試驗顯示上、下基準線分別為(?? ? ??)? = 5.61 ℃;(?? ? ??)? =?3.06 × ??? + 4.69 ℃；VPD 為飽和蒸汽壓與實際蒸氣壓之差值，單位為 kPa。
本研究利用 CWSI 對玉米進行三組試驗。試驗一顯示，玉米在灌溉後，前期會因停止灌溉而導致 CWSI 略為上升，達 0.35 左右，之後三天後會因為土壤水分不足而大幅上升增加至 0.8，建議將玉米之CWSI 控制在 0.35 以下；試驗二顯示 CWSI 的不穩定，推斷為天氣因素不佳，測量時為陰天，使得無法利用 CWSI 判斷植株的水分情況，建議在使用 CWSI 進行量測時須在晴天下收集數據，避免使用上的不準確性；試驗三顯示玉米的 CWSI 確實會因為灌溉有上下的變動，故本研究認為透過 CWSI 對玉米進行灌溉時程的制定是可行的。
最後則是找尋 CWSI 與土壤水分含量之間的相關性，盼能透過CWSI 換算出土壤水分含量。結果顯示 CWSI 與 40cm 深度內之土壤水分含量平均值進行迴歸分析結果最佳，決定係數為 0.82。故本研究透過 CWSI 推估出土壤水分含量是可以取代傳統的單點測量的窘境，加快測量速度並更便於灌溉管理。;Farmers used to irrigate based on their experience, the measurement of soil moisture content, and the estimation of evapotranspiration, stem water potential, and stomatal conductance, etc. However, these methods of measure may cause soil or plants damage and can only reflect the condition in a small local area. In this study, Crop Water Stress Index (CWSI) is used as an indirect measurement to quantify the water status of corn in northern Taiwan.
In order to monitor the water status of the corn through CWSI, the experiment is done to develop the upper baseline and lower baseline of the corn in northern Taiwan, which is (?? ? ??)? = 5.61℃ and (?? ? ??)? = ?3.06 × ??? + 4.69 ℃ , respectively, with ?? being leaf temperature; ?? being air temperature, and VPD being the difference between the saturated vapor pressure and the actual vapor pressure. The lower baseline (?? ? ??)? is the difference between the leaf temperature and the air temperature under the condition that the plant the plant performs potential evapotranspiration given sufficient soil water supply. The upper baseline (?? ? ??)? is the difference between the leaf temperature and the air temperature under the condition that the plant is under water stress and is unable to perform minimum evapotranspiration.
The experiment on corn was conducted to identify CWSI under three experiments. Based on the result of the first experiment, the CWSI slightly increased to 0.35 around 2 days after the irrigation is stopped. Due to the low soil moisture, the CWSI value substantially increased to 0.8 around 3 days. Thus, it is recommended that the CWSI of the corn should be controlled under 0.35.
According to the second experiment, result shows that the CWSI is unstable. It is likely that because of the poor weather condition, the CWSI cannot indicate the status of plants. As a result, it is suggested that experiments of monitoring the water status through CWSI should only be conducted under clear days, to avoid the inaccuracy while collecting data. The third experiment shows that the CWSI of the corn did show fluctuations caused by irrigation. It is feasible to perform irrigation management of corn through the monitoring of CWSI.
The soil moisture content can be estimated by CWSI. Experiments show the coefficient of determination between CWSI and the average of soil moisture content being 0.82. It is concluded that CWSI can replace the traditional single point measurement, improve the efficiency of measurement, and make it convenient for irrigation management. |
