**1. Introduction**

Globally, the effects of climate change are evident and affect the daily lives of people and the planet. One of its effects is water shortages in a large number of regions across the world. Water scarcity often results in reduced agricultural productivity due to shortages and/or poor water quality. Taking into consideration that agriculture consumes 70 percent of the available freshwater [1] with low efficiency [2], the need to find sustainable water resource management solutions becomes imperative.

Most of the existing research reports in the field of irrigation scheduling focus on the development of low-cost IoT-based solutions [3–5], the use of machine learning and fuzzy logic [6–8], and the use of different irrigation methods and models [9–11]. A comprehensive analysis regarding the research on smart irrigation systems was reported by García et al. [12],

**Citation:** Tsiropoulos, Z.; Skoubris, E.; Fountas, S.; Gravalos, I.; Gemtos, T. Development of an Energy Efficient and Fully Autonomous Low-Cost IoT System for Irrigation Scheduling in Water-Scarce Areas Using Different Water Sources. *Agriculture* **2022**, *12*, 1044. https:// doi.org/10.3390/agriculture12071044

Academic Editors: Alban Kuriqi and Luis Garrote

Received: 27 June 2022 Accepted: 13 July 2022 Published: 18 July 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

where a detailed overview on the recent trends on sensors and IoT systems for irrigation was presented. At the commercial level, there are many IoT systems that have been developed for multiple agricultural purposes, including irrigation (e.g., Libelium [13] and iMetos [14]). However, some of them only focus on weather and soil monitoring without taking into account crop water requirements (e.g., WatchDog [15] and Netsens [16]).

Recently, significant research has been reported on the development of IoT systems for water monitoring both in terms of quality and quantity [17–20]. A large number of these systems focuses on monitoring natural water sources, such as lakes and rivers [21–23]. Following the research performed in water monitoring, a lot of systems are commercially available with the most well-known being Libelium [13], as its price is relatively low compared to other solutions, but none can control different water sources for irrigation scheduling.

Following the Industry 4.0 revolution, a large variety of low-cost processors, controllers, electronic components, and sensors have become available, which can be used for developing low-cost IoT solutions. The most common example is the Arduino open-source microcontroller-based development board [24]. These boards provide, at a very low cost, all the characteristics needed for developing a monitoring/actuating device, namely, an embedded microprocessor, connections for power supply, analogue and digital I/O channels for interfacing with peripheral devices (e.g., sensors), dedicated channels (e.g., USB communication port), and a vast variety of different modules for various purposes (e.g., GSM modules). In addition, the extensive use of Arduino boards by a large community has allowed the establishment of a broad range of supported features, making these boards mature enough, and with great reliability and flexibility, which is necessary for precision agriculture applications [25]. For this reason, significant research has been reported during the last years on developing Arduino-based solutions for agriculture [26–28] and water monitoring [29,30]. Following this trend, the extensive use of Arduino boards has contributed to the development and further availability of a variety of low-cost sensors in the market, whose efficiency in agriculture has been investigated with positive results [31–33].

As agriculture may be conducted in an open environment, wireless data transmission is required. Many different types of wireless data communication protocols are used in agriculture [34], including broadband cellular network technology protocols (GPRS, 4G, and 5G), LPWA—Low Power Wide Area Network protocols (LoRaWAN, SigFOx, NB-IoT, and LTE-M), WLAN—wireless LAN protocols (Wi-Fi), and IEEE 802.15 Protocols (ZigBee and Bluetooth). Each one of them has its advantages and disadvantages in terms of power consumption, range coverage, and data collection rate.

In this context, the HYDROUSA H2020 project [35] objectives were the sustainable management of water and the increase in agricultural production in water-scarce areas by applying precision irrigation using water that comes from a variety of water sources (rainwater, groundwater, seawater, and wastewater). Therefore, the main aim of this study is to develop a reliable and accurate low-cost IoT system to monitor and control irrigation scheduling, which is able to operate using different water sources. To achieve this, the system was: (i) developed using open source hardware for minimizing its cost, (ii) capable of supporting a variety of sensors and actuators, (iii) evaluated for its accuracy, and (iv) validated for its functionality and capabilities on using different water sources for automating irrigation scheduling.

The innovation of the present study is the design and development of an Arduinobased low-cost IoT node with extensive energy autonomy, capable of autonomously handling the various water sources and applying precision irrigation based on weather data and plant requirements. This study can contribute to increasing irrigation sustainability, especially in water-scarce areas, as water coming from alternative water sources can be used for irrigation, minimizing the use of the conventional irrigation water sources.
