文 / 氣候變遷與永續發展國際學位學程莊振義副教授、王祥恆博士生

The farmers’ management strategies and field practices play a crucial role in the surface energy balance in surface-atmosphere interactions from the canopy structure to landscape scales in crop fields (Gutiérrez and Meinzer, 1994; Mahmood et al., 2014; Meyers and Hollinger, 2004). Besides, surface energy components can modify micro and regional climate (Sridhar and Anderson, 2017). In the past few decades, many studies reveal the effects of field practices (e.g., irrigation, pruning, weeding, and fertilization) on the yields in agricultural field (De Costa et al., 2007; Gail Smith et al., 1993; Mohotti and Lawlor, 2002) and from microclimate to regional scales (Alberto et al., 2011; Alter et al., 2015; Puma and Cook, 2010; Suyker and Verma, 2009).

The increasing surface humidity and downward longwave radiation on the regional scale induce warmer temperature and more precipitation when irrigation areas continually grew after the 1950s (Puma and Cook, 2010). Besides, the downwind area neighboring to the irrigated field has lower surface temperature and more precipitation (Alter et al., 2015). The effects of agricultural practice on the energy components had conducted at different crop fields, such as wheat, corn, and soybean (Alberto et al., 2011; Baldocchi, 1994; Eshonkulov et al., 2019; Gutiérrez and Meinzer, 1994; Ham and Heilman, 1991; Meyers and Hollinger, 2004; Suyker and Verma, 2009).

According to farmers’ experience and local knowledge, agricultural management strategies depend on crop species and their demands, such as weeding, pruning, watering, and fertilizing. Their strategies’ most important purpose is to increase their crop yield by controlling the microclimatic factors, such as the temperature, soil moisture, and radiation components (Constantin et al., 2019; De Costa et al., 2007).

Climate change and extreme weather factors, such as shifting precipitation patterns and heat waves, have affected the crop growth and yields from regional to global scales (Altieri et al., 2015; IPCC, 2014). To minimize extreme climate influences, Food and Agriculture Organization (FAO) promotes agroforestry management in tea fields (Bhagat et al., 2016). These management strategies include establishing more shading by planting taller trees and keeping a little weed to conserve more water. These kinds of practices are expected to have different surface coverage patterns, energy budget, and water budget on the surface in tea fields. However, it is worth noting that little research can supply quantitative evidence for microclimate patterns and parameters in the tea field with different management strategies.

Tea is an important perennial crop between different kinds of cash crops in many countries, particularly in Asia and Africa (Bhagat et al., 2016). To increase tea production, tea farmers apply different management strategies in their fields (Carr, 2010; De Costa et al., 2007; Mohotti and Lawlor, 2002). The tea fields’ applications are expected to have an apparent influence on surface-atmosphere interactions, such as energy balance, water conservation, and radiation interception.

To examine the roles of different field practices in the tea fields’ energy components, this study proposes a field observation of radiation budget, energy components, and canopy structure in the tea fields in Pinglin to characterize how the field practices affect energy patterns. These parameters and data could provide a vital reference for the regional study of climate change.

Pinglin is a small township located approximately 25 km southeast of Taipei City in northern Taiwan. It is hilly terrain and water protection area. The mean temperature is 19.5 °C, with the annual range from 12.8 °C in January and 25.6 °C in July. Winter monsoon and summertime orthographic lifting cause this area to have annual precipitation surpassing 4,000 mm, which is more than near downtown Taipei in 2,500 mm. The most important agricultural activity in Pinglin is growing tea because the suitable dominant soil type is red clay (Ultisol) with pH 4-6. Since this area has no apparent dry season, most tea planting field extremely relies on rainfall and dew to irrigation. In winter and summer, the tea farmers apply mild activities and make tea fields undisturbed. Before spring tea (harvest around April), tea farmers begin pruning for a better growing condition for new tea buds and weeding for less competition of nutrients and convenient for harvest.

Continuous measurement data can understand how the management strategies affect radiation budget (CNR1, Kipp & Zonen Ltd., Delft, Netherlands) and energy components (CSAT-3, Campbell Scientific, Inc., Logan, UT, USA; LI-7500, LI-COR Inc., Lincoln, NE, USA; and HFT3.1, Radiation & Energy Balance Systems Inc., Seattle, WA, USA). The field data were collected from 1 December 2018 to 17 June 2020 at two neighboring tea fields (121.7279°E, 24.9645°N) with different management strategies in Pinglin (Figure 1). These tea fields have almost identical surrounding environments and geographical conditions, but different farmers’ management strategies. The most crucial difference is that one is a commercial field (label as B1 in Figure 2) with herbicide usage and harvest by machine. The other (B2) is an organic-certified field with manual harvest and weeding.

The most obvious difference is that the organic-certified field in this study has more latent heat. Harvest bring reduced canopy coverage, and it decreases net longwave radiation and increases sensible heat. The field practices also modify the albedo in the field. The results show that weeding increases the albedo, and harvest decreases it. From the quantitative results, the tea field with more weed and harvest by hand can keep more moisture in the field. The results of this study are under review now.

Lately, eco-friendly planting has been advocated in the agricultural field (Kesavan and Swaminathan, 2008). FAO also encourages agroforestry planting strategies in the tea field against possible climate change (Bhagat et al., 2016). Several studies show more canopy coverage in the coffee field can reserve more soil moisture and decrease sensible heat (Gutiérrez and Meinzer, 1994; Lin, 2007; Lin, 2010). The results from our measurement data in the tea fields provide a quantitative reference as an encouragement for eco-friendly planting. Finally, the quantitative data offers a scientific basis for analysis and comparison for modeling from micro to regional scales.