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Top1. Introduction
Wireless sensor networks (WSN´s) are employed in a variety of applications, such as environmental and atmospheric monitoring, security, industry, domotics, bioengineering, mobile assets management, among others (Alippi, Anastasi, Di Francesco, & Roveri, 2009; Parra, Karampelas, Sendra, Lloret, & Rodrigues, 2015a). This paper presents one application for the agricultural sector. Water flow measurement allows the estimation of water supply to crops. One requirement for crops is the dispersion of water to maintain soil humidity. One of the most efficient and used types of irrigation on crops is the Irrigation Pressure System (Kim, Evans, & Iversen, 2008). The amount of pumped water and its quality in the irrigation system are fundamental in the production of the field. Water should not include thin particules as slit and clay, since they clog pipes and create flow measurement errors that may decrease the humidity diameter (the wet zone after the irrigation begins) (Martin, 2009).
Irrigation pressure systems are used on crops because they help saving water and eliminating seepage losses (National Resources Conservation Service, n. d.). Crops need constant humidity; therefore, the priority is maintaining the pressure on the pipes using adequate methods of sensing and monitoring water flow. The irrigation designer has to develop the scheme for the necessities of soils and crops such as pipe location, property loam, water flow, etc. Equation (1) shows the application rate (AR) in inches per hour, in a large cultivated field, depending on the volume applied per nozzle in gallons per minute (G), sprinkler spacing (Ss) and lateral spacing (Ls) (Kim et al., 2008; National Resources Conservation Service, n.d.).
(1)Cotton, corn and peanut farms are some examples of large agricultural fields. Water distribution in these cases is done with a central pivot moved by equipment as tractors or floating holder systems. The mean pressure used on this kind of irrigation process is higher than 30 psi (National Resources Conservation Service, n.d.).
Projects with specific capacity of liquid consumption require a measurement system for optimizing water use. Agricultural production is affected by evaporation water loss in the soil and crop transpiration; the ratio between these two facts is known as evapotranspiration (Keller, 2005). Sprinkler, mini-sprinkler, micro-sprinkler and dripping irrigation are the most common low pressure systems for semi-arid and arid areas. The designer chooses the type of irrigation, guided by soil texture, climate conditions, crop requirement, motor pumping, topography characteristics, etc. (National Resources Conservation Service, n.d.).
WSN require communication protocols to transmit data with small energy use (Kabara & Calle, 2012). Therefore, implementations of WSN often use protocols adequate to the specific application. Some studies propose protocols that may be useful in agricultural applications (Abd El-kader & Mohammad El-Basioni, 2013; Calle, Berdugo, Velez, & Kabara, 2017; Ojha, Misra, & Raghuwanshi, 2015). On the other hand, researchers developed wireless systems for smallholding crops (Karthikeyan, Karthikeyan, Narayanan, & Suresh, 2015; Kim et al., 2008; Smarsly, 2013). The studies measured different values in field tests but they did not measure water flow. Other studies propose WSN for water pressure measurements (Ntambi, Kruger, Silva, & Hancke, 2015). Measurements are taken outside the water pipe, unlike our proposed system. The literature also proposes different approaches to estimate the amount of water required in agricultural fields based on simulations (Nesa Sudha, Valarmathi, & Babu, 2011; Nikolidakis, Kandris, Vergados, & Douligeris, 2015).