Development of an IoT-Based Smart Watering System for Monitoring and Increasing Soil Moisture Content in “Tabtim Siam” Pomelo Garden in Pak Phanang District, Nakhon Si Thammarat Province, Southern Thailand

Globally, citrus fruits are the leading fruit crops. The three major citrus fruit crops are orange, mandarin, and pomelo in terms of their production and consumption [1]. In 2020–2021, the total production of citrus fruit was 98 Mt worldwide [2]. Citrus fruits have several active compounds such as vitamin C, carotenoids, essential oils, minerals, acridone alkaloids, flavonoids, limonoids, coumarins, and triterpenoids that are beneficial to health [3,4,5,6]. They also have antioxidant, antimicrobial, anti-inflammatory, anti-tyrosinase, antihyperlipidemic, and anticancer properties [7,8,9,10,11,12,13,14,15,16,17,18]. Regularly consuming these fruits can treat various diseases such as inflammation, muscle pain, coughs, ringworm infection, and stomach upsets [8]. Several environmental factors affect the growth and quality of citrus fruits. Among these, soil moisture content is the most critical factor that determines the plants’ growth, vigor, and productivity potential [19, 20]. The nutrient uptake of the plants depends on water availability in the soil. Lack of water at any stage affects the productivity and the quality of the fruits [20]. Large-scale loss of citrus plants was observed in India due to frequent drought and scarcity of water [21, 22]. Inadequate soil moisture limits the water supply to the roots and reduces the root conductivity directly [23, 24]. For citrus plants, no water deficit is considered when the soil moisture level is above 70% during their main developmental stages. A mild or moderate water deficit is considered when the soil moisture content is 50%–70%. Severe water deficit happens when soil moisture is <50% [25]. Fruit quality traits and production absolutely depend on soil water availability [26]. Maintaining a suitable range of soil moisture content in citrus orchards is crucial.

In Thailand, pomelo is one of the top 10 economic fruit crops [1]. In 2020, Thailand exported 25,283.07 tons of fresh pomelo, valued at 1,203.18 million baht [27]. Pomelos are cultured in 60 out of the 76 Thai provinces. The central producing provinces are Phichit, Samut Songkhram, Nakhon Pathom, Prachinburi, and Nakhon Si Thammarat. The total planting area is approximately 94,458 rai, and the average yield is 2,394 kg/rai [28]. Among various types of pomelos, the demand for Tabtim Siam or ruby pomelo is increasing day by day in domestic and international markets, especially in China, Taiwan, Malaysia, Singapore, and Brunei because of their pulp’s ruby red color, as well as sweet, juicy, soft, and flavorful aroma. Nowadays, the price of one Tabtim Siam pomelo fruit is 150–250 baht (4–7 USD) from the hands of the farmers [29]. Tabtim Siam Pomelo is mainly grown in Pak Phanang District in Nakhon Si Thammarat Province, Thailand, and it is known as the geographical indication (GI) product of Pak Phanang [29]. The total planting area is approximately 3,933 rai, and the average yield is 2,885 kg/rai [30]. Although the demand for pomelo is increasing nowadays, the quality of pomelo is not enough to fulfill the market demands. The value of ruby pomelo depends on the fruit’s quality. High-quality fruits are defined as suitable fruit sizes (>1 kg weight/fruit) with no scars on the fruit surface. The color of the peel must be bright green, and the fruit flesh must be dark ruby red [31]. These qualities depend on many environmental factors, among which soil moisture content is the most important factor. They require soil moisture ≥70% in their root zone, but not >30 cm deep during their vegetative growth period. Tabtim Siam pomelo needs a consistent water supply for its photosynthesis process. However, if there is excessive water, it will have a severe impact on the root system. In case of high soil water content or lack of water, the quality of the fruit will be poor. As a result, the fruit will be small and may have a bitter taste [32]. Therefore, appropriate water management is necessary in pomelo orchards to maintain a soil moisture content of ≥70%. In recent years, technology has brought new changes to agricultural production. It not only increases agricultural output but also effectively improves the quality of agricultural products [33]. Nowadays, smart watering systems are used to monitor and control various environmental factors to increase the growth of trees and the quality of products. For example, a smart watering system was used to control the irrigation process in strawberry greenhouses in Greece [34]. Another study in China used a smart watering management system to control the soil moisture content in tomato farms [35]. In India, a smart water management system was used to control the soil’s moisture content, temperature, humidity, and water flow to improve the irrigation process on agricultural farms [36]. In Thailand, a smart watering system was used to increase humidity and decrease thrips inside mangosteen canopy [37, 38].

This study aims to develop an IoT-based smart watering system to monitor and maintain a soil moisture level of ≥70%, even when the air temperature is very high. Usually, there is a negative relationship between air temperature and soil moisture, and a low level of soil moisture content during high air temperature affects the growth of plants. Therefore, keeping the soil moisture content at least 70% during the high temperatures is essential. Developing a smart watering system for maintaining the required soil moisture level in Tabtim Siam ruby pomelo orchards will help the farmers to increase their pomelo production and earn more money.

This work’s novelties include developing a novel Internet of Things (IoT) sensor-based watering system for monitoring temperature and soil moisture data. The system uploads sensor data to the IoT cloud using an Android or iPhone Operating System (iOS) phone and stores them for further analysis.

In this study, a smart watering system was developed and used successfully to monitor and increase soil moisture content in the Tabtim Siam pomelo garden. Soil moisture content affects the growth, quality, and production of citrus fruits [39,40,41]. When the soil moisture content is too low, the fruits will be shriveled, the yield of citrus fruits will decrease, and the weight of each fruit and vitamin C level will decrease [42]. Several studies show that low soil water content negatively affects plant water status, reducing leaf water potential and gas exchange [43,44,45]. Additionally, water deficit affects the content of amino acids, organic acids, and sugars in the fruit [46]. Fruit splitting and nutritional deficiencies also occur due to a lack of water in the orchards [47]. In the case of pomelo trees, if there is a lack of water, the growth of trees becomes delayed, insects attack pomelo trees easily, the flowers and immature pomelos fall off, and the matured pomelos lack sugar, juice content, and quality [28, 31, 40]. Low soil moisture content affects pomelos and other fruits in Thailand. Therefore, several intelligent watering systems were developed and used in different fruit orchards. For example, an intelligent irrigation system was developed to control soil moisture inside a durian garden in Nakhon Si Thammarat Province [48]. An intelligent irrigation system was developed to monitor and control a cassava garden’s soil moisture content in Nakhon Ratchashima Province [49]. Another study developed and used a sensor-based watering system to monitor and control the soil moisture levels in melon orchards in Nakhon Pathom Province [50]. The details of some existing smart watering systems are provided in Table 3.

It was also observed that the smart watering system could hold more soil moisture content (%) compared with the conventional watering system, even at very high air temperatures (e.g., >30°C). The conventional watering system also maintained soil moisture level by 67%–68% when the air temperature was very high, but it could not reach up to 70%, which is the required level for Tabtim pomelo. Naturally, moisture content in soil is controlled by several factors but primarily by air temperature [51]. Air temperature negatively affects soil moisture, and soil moisture retention, diffusion, and loss can be impacted by rising air temperatures [52, 53]. In most cases, air temperature negatively correlates with soil moisture [54, 55]. However, artificial watering/soil irrigation can increase the moisture content in the soil if it is done properly and, in that case, it is possible to get a positive relationship between air temperature and soil moisture, which is observed in our study. Another study also showed that providing water inside an eggplant orchard increased soil moisture content and maintained moisture level by nearly 60% even when the temperature was 30°C [56]. Our study also found that the smart watering system maintained moisture levels by 70% even when the temperature was >30°C. This happened because water was automatically provided for 15 min at 12.30 p.m. and 3.30 p.m. when the temperature was >30°C. This indicates that watering time is also essential to maintain the required moisture content in the soil.

Future research could be conducted to develop an innovative and cost-effective IoT sensor-based watering system that will not only monitor the soil moisture but also provide or stop watering automatically based on the required soil moisture level (%). This system could be used more effectively in fruit/vegetable orchards where maintaining soil moisture (%) is crucial.

This study designed and used an IoT-based smart watering system to monitor and increase soil moisture level effectively inside a Tabtim Siam ruby pomelo garden. This study also observed that soil moisture was at the required level even when the air temperature was very high. It presumably happened because of the watering time management by using the smart watering system. Though farmers provided water twice daily (30 min each time), it did not help them to keep the soil moisture at the required level when the temperature was high. On the contrary, in the smart watering system, providing water four times (15 min per time) daily maintained the required level of soil moisture during high temperatures, and it used the same amount of water that the farmers use in their conventional watering method. Therefore, this study shows that using a smart watering system and providing water systematically helps the farmers to keep the soil moisture level of ≥70% in the ruby pomelo orchards. This system might be helpful for other fruit orchards requiring high soil moisture. Now, this smart watering system needs to be familiar to the farmers who cultivate pomelo or other fruits in southern Thailand, so that they will be able to use this system easily, increase the quality and quantity of the fruits, and earn more money.