探討田間管理在茶園中的能量收支和土壤水分的角色

Abstract

在農田中，從植被到地景尺度的地表能量平衡在地表和大氣的交互作用中扮演著必要的關鍵角色，它明顯地受到農民的田間管理和施作措施的影響。這些田間施作措施影響了氣象參數、土壤溫度和土壤水分。為了瞭解農民的田間施作措施如何影響多年生農作物的田間微氣候，本研究在北台灣的淺山地區選擇兩個相鄰但由不同農民管理的茶園（一個是慣行管理的茶園，另一個是有機認證的茶園），進行長期的輻射預算、能量收支、樹冠層溫度、蒸氣壓差、土壤溫度和土壤水分的觀測。結果顯示，輻射預算的差異很小（僅占淨輻射的1%）。然而，能量收支因為兩個茶園高度分歧的管理方式而具有顯著差異（有機茶園比慣行茶園少了10%的可感熱通量、多了25%的潛熱通量）。除此之外，與有機茶園相比，慣行茶園的土壤日夜溫差較高（0.45°C），而有機茶園的土壤水分流失的速度較快（-0.93% d-1），慣行茶園則是（-0.46% d-1），這個結果呼應了慣行茶園具有較多的可感熱通量以及有機茶園具有較多的潛熱通量。本研究的發現指出，有機的茶園管理方式可以降低可感熱通量的能量分配，並且增加潛熱通量的能量分配，因此能減少日夜的溫度變化以及降低蒸氣壓差。在長期的能量通量方面，有機的管理方式可以減少地面的加熱效果。本研究發現，在較小的時間尺度下，慣行的管理方式明顯增加了可感熱通量（中午時可達51.5%），相較於有機的管理方式僅增加9.6%。本研究提供了在不同的茶園管理方式之下的全面的基礎數據，可作為水資源保育的參考資料、從微小到區域尺度的氣候模式的定量分析的參考數據、評估在不同的未來氣候情境下，農民工作時的熱壓力指數的基礎資訊。

The surface energy balance from canopy to landscape scales in crop fields plays an essential role in surface-atmosphere interactions. It is strongly influenced by the management strategies and field practices of farmers. These practices also affect the micrometeorological parameters, including energy partitions, soil temperature, and soil moisture. To characterize how different agricultural practices of farmers affect the microenvironment in perennial crop fields, a long-term observation of the radiation budget, energy components, canopy temperature, vapor pressure deficit, soil temperature, and soil water content was conducted in two neighboring tea fields with different management strategies (a conventional operation field and an organic-certified field managed by different farmers) in a hilly terrain area in northern Taiwan. The results showed that the difference in the radiation budget in these two tea fields was minor (only 1% for net radiation). However, the differences in the energy components were more significant (sensible heat was 10% lower and latent heat was 25% higher in the organic-certified field than in the conventional field) due to highly distinct practices in these two fields. Furthermore, the higher diurnal soil temperature (0.45 °C) contributes to the more considerable sensible heat flux in the conventional field. On the other hand, in the organic-certified field, the faster-decreasing rate of (-0.93% d-1) soil water content is consistent with the greater latent heat flux. This finding implies that the organic-certified application could lower the partitioning of sensible heat flux and increase the latent heat flux, thereby reducing the temperature variation and decreasing the vapor pressure deficit. The organic-certified field reduced the surface heating in terms of the long-term energy patterns. The findings of this study also indicate that field practices in the conventional field can increase the sensible heat flux (51.5% at noontime) on short-term time scales, while it is only 9.6% in the organic-certified field. Furthermore, this study offers primary data in the comprehensive understanding of tea field practices, a scientific basis for in-field water conservation, quantitative analysis for modeling from micro to regional scales, and essential information for estimating heat stress index for field workers under different future climate scenarios.