Article
An Automatic Irrigation Control System for Soilless Culture of Lettuce
Zhigang Liu 1,* and Qinchao Xu 2
- School of the Environment and Safety Engineering, Institute of Environment Health and Ecological Security, Jiangsu University, Zhenjiang 212013, China
- College of Engineering, Huazhong Agriculture University, Wuhan 430070, China; hlxqc@mail.hzau.edu.cn
* Correspondence: liuz.g@163.com; Tel.: 86-511-8879-0955
Received: 17 September 2018; Accepted: 15 November 2018; Published: 20 November 2018 check Eoj
Abstract: To achieve precise measurement of moisture content in the substrate and intelligent water-saving irrigation, a simple and low cost automatic irrigation control system based on ZigBee wireless network has been developed. A software with irrigation strategy was proposed based on the models of substrate wetting pattern, lettuce root zone and the evapotranspiration. The system could detect substrate moisture in real-time and irrigate automatically according to the threshold of substrate and the irrigation strategy. The average fresh weight per plant under intelligent irrigation are 16.60% and 11.37% higher than manual control irrigation at least in different growth stages in spring and summer, the average drainage rate of intelligent irrigation is 16.08% and 17.06% smaller than manual control irrigation in spring and summer, and the irrigation water use efficiency of intelligent irrigation is 68.03% and 98.61% higher than manual control irrigation in spring and summer. The results show that the system is a promising tool for scientific and rational irrigation decision.
Keywords: irrigation scheduling; irrigation control system; soilless culture; ZigBee; lettuce
Introduction
Lettuce, one kind of shallow rooted and moisture sensitive crop, is the most popular vegetable with the highest consumption rate throughout the world [1,2]. Moisture stress is being crucial for yield and quality [3], because of the water condition of the root zone is one of the most important factors for lettuce cultivation.
Soilless culture is a promising technique largely applied in greenhouse horticulture due to its multiple advantages [4,5]. In substrate culture, water must be precisely controlled to the crop because the water holding capacity of the substrate is very low and substrate are usually inert [6,7].
Lettuce has been grown with substrate in greenhouse for many years [8,9]. However, most lettuce growers tend to irrigate when they observe crop wilting during the day and the amount of irrigation they apply is based on their experience [10]. Obviously, an adequate irrigation control is of great importance to achieve a profitable production of lettuce with high yield and quality.
An automatic irrigation system was designed based on the potential evapotranspiration for irrigation control under greenhouse climatic conditions [11,12], soil moisture sensors [13,14] and leaf temperature sensor [15]. Due to the advantages of straightforward installation, and low cost in wiring and piping in wireless technologies, autonomous irrigation with sensors in agricultural systems has been intensively explored in the last years [16–19], however, most of these studies were conducted on soil, the substrate physicochemical properties are significantly difference from soil, and these differences have great impact on substrate water evaporation capacity, substrate moisture migration, crop root growth in substrate, and substrate moisture detection, therefore, the automatic irrigation control system for soil cause waste of water or water stress to crops in substrate cultivation. For better
Water 2018, 10, 1692; doi:10.3390/w10111692 www.mdpi.com/journal/water
irrigation management, substrate water evaporation capacity, substrate moisture migration, crop root growth in substrate, and substrate moisture detection are required.
The main objective of this study were (i) to develop an automatic irrigation control system applied in soilless based on ZigBee wireless sensor networks; (ii) to evaluate the performance of the developed automated system under greenhouse conditions. This low cost technology can easily be installed and used in a variety of settings including greenhouse, home gardens and small farms.
Material and Methods
The irrigation control system is illustrated in Figure 1. The base station unit is the initiator of the ZigBee network construction, which controls the entire network. The function unit (Zigbee terminal and Zigbee coordinator) is responsible for collection and transition of the irrigation control signal and substrate moisture signal, including air temperature, solar radiation and so on.
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