利用Hydrus-1D與土壤水力特性探討作物灌溉策略與田間含水量

Abstract

高精準灌溉策略能同時確保糧食安全及永續管理農業水資源。灌溉強度及時間會顯著影響灌溉效率與作物生長。然而，過去研究鮮少針對灌溉強度、時間及期距並搭配土壤質地做系統性的探討。此外，決定灌溉策略的關鍵參數「田間含水量」的定量方法，也尚未有統一定論。因此本研究目的為探討不同土壤質地適合的灌溉強度與對應策略，並重新檢視田間含水量的量化方式，其研究結果將有助於訂定高精準灌溉策略。本研究首先彙整臺灣土壤資料，分析土壤水力特性並比較不同的田間含水量量化方式。進一步利用Hydrus-1D模式推估田間含水量與有效水分含量，搭配土壤與作物(柑橘類果樹)等參數進行灌溉及排水模擬。透過分析得出不同灌溉強度與其對應的田間灌溉效率，並以此回歸出不同土壤質地之合適灌溉強度、時間及期距，制定出合適灌溉策略公式。另外，本研究也補充探討不同地下水位對灌溉策略之影響，及不同灌溉強度之CN值變化，提供未來作物模式參考。此外，本研究也發現當地下水位較深時，Hydrus-1D模式的排水模擬無法重現排水實驗結果，主因為排水過程中土壤會產生水力連續性中斷及角落流現象，造成實驗排水速度遠低於模擬。修正後的Hydrus-1D模式排水模擬除了可以吻合實驗結果外，也用於修正灌溉策略。修正後的灌溉策略與傳統田間張力模擬的灌溉策略相比，發現其灌溉期距可以延長好幾小時，且所需每日灌溉量較少但產量卻可維持。因此代表過往的田間含水量推估方式，可能會高估所需的灌溉量與頻率。最後本研究點出以現有方式推估出的田間含水量無法完善代表真實田間含水量，未來應投入更多研究以增進對田間含水量的掌握度。

High-precision irrigation strategies can simultaneously ensure food security and sustainable management of agricultural water resources. Irrigation intensity and time can significantly affect irrigation efficiency and crop growth. However, few previous studies have systematically discussed the irrigation intensity, time and interval in combination with soil texture. In addition, the quantitative method of 'field capacity', a key parameter that determines irrigation strategies, has not yet been unified. Therefore, the purpose of this study is to explore the appropriate irrigation intensity and corresponding strategies for different soil textures, and to re-examine the quantification method of field capacity. The research results will help to formulate high-precision irrigation strategies. This study first compiled soil data in Taiwan, analyzed soil hydraulic properties, and compared different methods of quantifying field capacity. The Hydrus-1D model was further used to estimate the field capacity and effective water content, and the irrigation and drainage simulations were carried out with parameters such as soil and crops (citrus fruit trees). Through analysis, different irrigation intensities and their corresponding field irrigation efficiencies were obtained, and then the appropriate irrigation intensity, time and interval of different soil textures were regressed, and the appropriate irrigation strategy formula was formulated. In addition, this study also explores the influence of different groundwater levels on irrigation strategies and the changes in CN value of different irrigation intensities, so as to provide a reference for future crop models. Furthermore, this study also found that when the groundwater table was deep, the drainage simulation of the Hydras-1D model could not reproduce the drainage experimental results, mainly because the soil would produce hydraulic continuity interruption and corner flow during the drainage process, resulting in the experimental drainage rate much lower than the simulation. The modified Hydrus-1D model drainage simulation can match the experimental results and can also be used to modify the irrigation strategy The modified irrigation strategy was found to extend the irrigation interval by several hours compared with the irrigation strategy of the traditional field tension simulation, and required less daily irrigation while maintaining yields. Therefore, the method of estimating field capacity in the past might overestimate the amount and frequency of irrigation required. Finally, this study points out that the estimated field capacity by the existing method cannot fully represent the real field capacity, and more research should be invested in the future to improve the grasp of the field capacity.