Weighing lysimetric system for the determination of the water balance during irrigation in potted plants

doi:10.1016/j.agwat.2016.10.006

Agricultural Water Management

Volume 183, 31 March 2017, Pages 78-85

https://doi.org/10.1016/j.agwat.2016.10.006 Get rights and content

Highlights

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Innovative system able to measure instantaneous evapotranspiration during irrigation.
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An evapotranspiration decrease has been observed within irrigation periods.
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System will allow to determine evapotranspiration in different irrigation conditions.
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Filtering techniques are essential to obtain instantaneous evapotranspiration.

Abstract

In years, the availability of water for irrigation is one of the main problems in Mediterranean Agriculture. That is why new technologies must be used to achieve proper irrigation management which is the main determinant of the quality and quantity of harvests and involves determining crop water needs. This paper presents a study for the development and implementation of an instrumentation system capable of accurately determining water balance during irrigation periods using a weighing lysimeter for potted crops. The mechanical structure of the lysimeter was designed and validated by our research group in previous works. In the design, the main requirements were high precision and low cost to make it affordable to most farmers. For this reason, the system was implemented using an open source platform and precision instrumentation to ensure accuracy of the measurements. A high-precision flowmeter was used to monitor the supplied irrigation water. The system was also capable of sending data wirelessly to a server in the cloud so they could be later queried from any device with Internet access. Field trials were conducted in order to collect data in both irrigation and non-irrigation periods. The application of filtering techniques was required, so a Savitzky-Golay smoothing algorithm was selected to obtain reliable data of instantaneous evapotranspiration. In the data analyzed, a decrease between 10% and 20% was observed in the hourly evapotranspiration during the irrigation intervals.

Introduction

Water scarcity is one of the main problems of the Mediterranean agriculture, especially in semiarid regions of the southeast of Spain. In addition, the progressive worsening of weather conditions, more and more extreme as a result of the impact of droughts and climate change, further underscores the need for adaptation developing efficient methods to optimize the use of water (Pérez-Sánchez and Senent-Aparicio, 2015). To do this, new technologies need to be exploited making them affordable to farmers with limited economic resources. In this context is framed the Spanish National Strategic Plan for Sustainable Modernization of Irrigation (MAGRAMA, 2014) whose main objective is the consolidation and modernization of existing irrigation systems in order to increase water savings through technological development applied to management of available water resources and, ultimately, to the optimum irrigation scheduling.

The region of Murcia, in particular, is severely hit by a gradual and progressive desertification. Low rainfall, and the use of saline water call for new strategies and methods for a region mainly engaged in irrigation agriculture (over 200,000 ha). The water management and irrigation scheduling methods used by most of the farmers are outdated; they are based mostly on humidity and salinity measurements within the roots zone, and a free decision making from the interpretation of these data (Bachand et al., 2014).

To make a proper irrigation scheduling it is necessary to determine the plant water needs. For this purpose different methods are used, such as models obtained from meteorological variables, soil sensors, as well as through direct measurement of the water balance with weighing lysimeters (López-Urrea et al., 2014, Ruiz-Peñalver et al., 2015, Vera-Repullo et al., 2015). Meteorological variables and soil sensors do not provide accurate calculation of the crop evapotranspiration (ET_c) since it is estimated indirectly by established formulas such as the Penman-Montheith (Allen et al., 1998). Image processing has also been used to obtain good estimates of the ET_c at a reduced cost (Escarabajal-Henarejos et al., 2015, García-Mateos et al., 2015), but a comprehensive calibration process is required for each particular species. Nevertheless, weighing lysimeters can be used to directly determine the ET_c (previously making a calibration and validation of the equipment), and thus establish the exact amount of water needed by a crop. Since data obtained from weighing lysimeters are more accurate and reliable, these are frequently used to validate data obtained with other methods (López-Urrea et al., 2006, Vaughan et al., 2007).

A lysimeter is a device used in agronomy to measure the volume of incoming water (rainfall and irrigation) and water coming out (drainage, evapotranspiration) of a container containing an isolated mass of soil (Payero and Irmak, 2008). Different types of lysimeters are commonly used by agronomists for calculating evapotranspiration, such as volumetric lysimeters and weighing lysimeters. The latter are the only ones that allow us to calculate evapotranspiration directly using a mass balance. The main drawback of using weighing lysimeters is that they usually require civil work which entails high costs. Moreover, in the majority of cases, lysimeters determine the ET_c accumulated over hourly and daily intervals, but do not have enough accuracy for obtaining it in shorter time intervals. For these reasons, the Agromotic and Sea Engineering research group developed a lysimeter for crops in pots (Ruiz-Peñalver et al., 2015) based on an easily portable and fast installation light metal structure. This first equipment was installed and validated in different field experiments using both commercial data loggers (Campbell CR1000) (Ruiz-Peñalver et al., 2015) and ad hoc conditioning and electronic systems (Jiménez-Buendía et al., 2015). Data collected with this lysimeter made it possible to accurately obtain ET_c values daily, hourly and every minute at low cost. This increase in accuracy led to pose the following challenge: what happens to ET_c during irrigation? Within irrigation intervals, ET_c was assumed to follow a linear trend so it was estimated using a linear interpolation between values at the beginning and at the end of irrigation. That is why research continued in order to develop an instrumentation system that had sufficient accuracy to work out the ET_c in the aforementioned irrigation periods. It is in this context that this paper presents the design and development of the measuring equipment for pot lysimeters implemented with reliable, inexpensive, open-source hardware and software platforms. Special attention has been paid to the necessary instrumentation to accurately measure the water supply as it is essential in determining the water balance.

This paper is organized as follows. Section 2 describes the instrumentation and electronic devices, software programming tools and acquisition and filtering techniques applied during and after data collection. Then, Section 3 presents and discusses experimental results, and finally, Section 4 is devoted to the conclusions.

Section snippets

Lysimeter

The system is based on a weighing lysimeter for potted plants formerly developed by our research group (Ruiz-Peñalver et al., 2015). As shown in Fig. 1, the triangular platform that supports the pot rests on three load cells located at their vertices and are used to measure the weight. A fourth load cell is responsible for measuring the weight of the drainage tank. The four load cells were constituted by temperature-compensated strain gauges (full Wheatstone bridge configuration). The model

Results and discussion

Fig. 5 depicts the overall structure of the developed system where details of the interconnection between the different elements are shown. Through the designed shield, Arduino Yun performed the acquisition of signals from the load cells, pulses from the flow sensor and controlled the motorized valves for emptying the drainage tank. The device logged all data on an SD card and sent them through the two available communication channels: (i) via the USB (prog) connection to a computer where the

Conclusions

This work has presented an electronic instrumentation system and associated software applications that improve the weighing lysimeter designed and validated by our research group in previous works. One of the key enhancements has been the addition of a low-range high-resolution flow sensor capable of accurately measuring water supply. In this way, the system allows to determine actual evapotranspiration during irrigation rather than estimating it. This is a novelty over existing systems so far

Acknowledgments

The authors wish to acknowledge, with gratitude, the technical assistance provided by Telenatura EBT, S.L. This work was supported by the Ministry of Economy and Competitiveness through the project with reference AGL2015-66938-C2-1-R “Automated Irrigation PROgramming system based on weighing LYSImetry and soil salinity, with remote supervision of the crop vegetative state (PROLYSI)”.

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View full text

Weighing lysimetric system for the determination of the water balance during irrigation in potted plants

Highlights

Abstract

Introduction

Section snippets

Lysimeter

Results and discussion

Conclusions

Acknowledgments

Crop Evapotranspiration: Guidelines for Computing Crop Water Requirements, FAO Irrigation and Drainage Papers

Differentiating transpiration from evaporation in seasonal agricultural wetlands and the link to advective fluxes in the root zone

Sci. Total Environ.

Getting Started with Arduino

Sprinkler irrigation changes maize canopy microclimate and crop water status transpiration, and temperature

Agron. J.

Water balance and evapotranspiration monitoring in geotechnical and geoenvironmental engineering

Digital photography applied to irrigation management of little gem lettuce

Agric. Water Manag.

Study and comparison of color models for automatic image analysis in irrigation management applications

Agric. Water Manag.

A data acquisition system based on outlier detection method for weighing lysimeters

Metrological Regulation for Load Cells

Development and assessment of a network of water meters and rain gauges for determining the water balance. New SCADA monitoring software

Agric. Water Manag.

An evaluation of two hourly reference evapotranspiration equations for semiarid conditions

Agric. Water Manag.

Consumptive water use and crop coefficients of irrigated sunflower

Irrig. Sci.