Development of a smart watering system for controlling humidity inside mangosteen canopy in Nakhon Si Thammarat province, Southern Thailand

Mangosteen (Garcinia mangostana) is considered the “queen” of the fruit in Thailand due to its taste and nutritional value. Mangosteen is a popular agricultural crop in Thailand, especially in southern and eastern Thailand. They are economically important both for domestic consumption and export. The major production comes from Thailand, Malaysia, Indonesia, and the Philippines. Thailand is the largest producer globally, and most of the production comes from southern and eastern provinces (Thongjua and Thongjua, 2015). The planting area of the mangosteen was 316,413 rai (6 rai = 1 ha) in 2006–2007, which was planted in southern and eastern Thailand (Pankeaw et al., 2011). Among southern provinces, most of the mangosteen production comes from Nakhon Si Thammarat province. From 2018 to 2021, the total production of mangosteen in Thailand, southern Thailand, and Nakhon Si Thammarat province was 1,146,295 kg, 567,601 kg, and 202,423 kg, and their values were 112,336,996 Thai Baht (THB), 55,624,898 THB, and 19,837,454 THB, respectively (Office of Agricultural Economics, Ministry of Agriculture and Cooperatives, 2022). Because of the high demand for mangosteen in international markets, Thailand exports mangosteen to different countries like Canada, Japan, Hong Kong, China and Taiwan ( Ongkunaruk and Piyakarn, 2011; Pankeaw et al., 2011).

In Nakhon Si Thammarat province, mangosteen culture is important because they produce a huge revenue for this Province (Musik, 2020). The value or market demand of mangosteen depends on the quality of the fruits. High-quality mangosteen is defined as a good fruit size (>70 g/fruit), no scar on the fruit surface, no translucent flesh disorder, and no fruit gamboge (Pankeaw et al., 2011). The common cause of scars on fruits' surfaces is thrips (Thripidae: Thysanoptera) infestation. Typical symptoms of the mangosteen fruit affected by thrips are silvering of the skin, pale yellow to brown discolouration, and elongated and patchy scars that may cover the entire fruit surface. Heavily scarred skin can sometimes prevent fruit development which causes smaller-sized fruits than standard size (Affandi et al., 2008). Thrips also damage flowers, young fruits and young leaves and decrease the quality of the fruits, causing economic loss. Both local and International markets dislike the rough scarring on the fruit surface, and the price of mangosteen at the farmers' level is determined based on the quality of the mangosteen. The production of high-quality mangosteen is less than 60% of the total output (Thongjua and Thongjua, 2015). In 100% mangosteen gardens, there is thrip damage (Pankeaw et al., 2011).

Thrips create scars not only on mangosteen but also on other fruits such as apples (Childs, 1927; Jacobs, 1995), grapes (Mcnally et al., 1985), and avocados (Dennill and Erasmus, 1992; Hoddle and Morse, 1997). Several climatic factors affect thrips population and distribution, such as humidity, temperature, rainfall, and wind (Gahukar, 2003; Waiganjo et al., 2008; Akram et al., 2013; Thongjua and Thongjua, 2015). Dry weather with moderately high temperatures increases thrips numbers. On the other hand, a wet season with relatively high humidity decreases thrips numbers (Waiganjo et al., 2008). Among many climatic factors, humidity is the one that affects the thrips distribution most (Waiganjo et al., 2008). A negative relationship was observed between humidity and thrips populations ( Akram et al., 2013; Thongjua and Thongjua, 2015). It indicates that high humidity can decrease the thrips populations and their distribution in the orchards.

This study aims to increase the humidity inside mangosteen canopy in Nakhon Si Thammarat province by developing a smart watering system. Thus, it can control the thrips populations and their distribution inside the mangosteen canopy. The development of smart watering system for controlling humidity as well as thrips inside mangosteen canopy can help the farmers to increase their mangosteen production and earn more money. Several previous studies developed and used smart watering systems for various purposes; for example, a smart watering system was used to control the irrigation process in a mango orchard in Spain (Zuazo et al., 2021). Another study in China used a smart water management system to control the soil moisture content in a mango orchard (Wei et al., 2017). A smart watering system was utilized to improve the irrigation process in mangosteen and durian orchards in Thailand (Cheychom et al., 2019; Musik, 2020). In India, a smart water management system was used to control the soil moisture content, temperature, drought of water, and to improve the irrigation process in several orchards such as: cauliflower, rice, long gourd, cotton, chilli, wheat, onion, and brinjal (Alok et al., 2016). In New Zealand and Australia, a smart sensing system was developed for nitrate monitoring in surface and groundwater in the agricultural industry (Alahi et al., 2017a, 2017b, 2018a, 2018b, 2018c, 2022). Moreover, smart watering systems were also developed for monitoring water quality in small fisheries farming and other agricultures (Akhter et al., 2021a, 2021b). The development of the smart watering system is explained in the second section.

In this study, we successfully developed a smart watering system for controlling humidity in the mangosteen garden. Previously, smart watering systems were developed and used in several orchards such as chestnut tree gardens, durian gardens, and mangosteen gardens for controlling the irrigation processes and several weather factors (Mota et al., 2018; Cheychom et al., 2019; Musik, 2020).

In the control system in our mangosteen garden, the humidity falls below 80% from 9 o'clock in the morning to 17 o'clock in the late afternoon, which can create a suitable environment for thrips and other pests. Previously it has been observed that low humidity is ideal for thrips populations, and it can create an outbreak of thrips (Mukawa et al., 2011). A negative relationship was also found between humidity and thrips populations (Thongjua and Thongjua, 2015). It means that the thrips are higher in numbers during low humidity and can destroy the fruits in orchards. They affect the young leaves, flowers and young fruits of mangosteen (Thongjua and Thongjua, 2015), chestnut (Mota et al., 2018), and strawberry (Allen and Gaede, 1963). They also affect several types of vegetables such as cucumbers, tomatoes, and sweet peppers (Rosenheim et al., 1990; Welter et al., 1990; Shipp et al., 1998; Hao et al., 2002). Thrips can damage cucumbers in two different ways; they leave scars on the cucumbers and change their shapes, affecting their production (Rosenheim et al., 1990). Another research showed that infestations of Thrips in cucumbers could decrease the tendrils number, leave numbers, and increase the plant mortality (Welter et al., 1990). In the case of tomatoes and sweet peppers, thrips can cause silvery and bronzy colours that affect their appearance and decrease their market value (Shipp et al., 1998). Thrips can also damage these vegetables by feeding their leaves and flowers. Their feeding modifies the carbon allocation in these plants (Shipp et al., 1998; Hao et al., 2002). Therefore, thrips decrease the quality of fruits and vegetables and cause economic loss. In the case of mangosteen orchards, if thrip outbreak occurs when the fruits are young, it creates scars on the fruit surface and reduces their value to the customers (Thongjua and Thongjua, 2015). However, high humidity is not suitable for thrips populations and it can suppress their populations by killing larvae, and adult populations (Thongjua and Thongjua, 2015). That is why it is important to control the humidity in fruit gardens for controlling thrips. We observed that our smart watering system is able to increase the humidity successfully compared to the control system which could control the thrip populations inside mangosteen canopy.

The present study implies the importance of using our smart watering system to increase the humidity inside the mangosteen canopy when needed. This system might be helpful for other orchards where high humidity is required. Since this system successfully increases the humidity, it presumably controls the thrips populations, but further research is needed to test that. This smart watering system needs to be socialized and familiar with the mangosteen farmers in Thailand thus, they can understand the importance of the system to control humidity in their mangosteen orchards.