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Development of Clemson variable-rate lateral irrigation system
Computers and Electronics in Agriculture 68 (2009) 108–113
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Computers and Electronics in Agriculture journal homepage: www.elsevier.com/locate/compag
Development of Clemson variable-rate lateral irrigation system夽 Young J. Han ∗ , Ahmad Khalilian, Tom O. Owino, Hamid J. Farahani, Sam Moore Department of Agricultural and Biological Engineering, Clemson University, Clemson, SC 29634-0312, United States
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Article history: Received 22 September 2008 Received in revised form 16 March 2009 Accepted 4 May 2009 Keywords: Irrigation Precision agriculture Variable-rate irrigation Instrumentation Lateral-move
a b s t r a c t Crops in the Southern United States are generally produced in fields which are known to have a high degree of variability in soil type, water holding capacity, infiltration rates, and other major factors which affect crop production. In these fields, the ability to turn irrigation water on or off or apply variably to different segments of the field is advantageous over the conventional uniform application. A variable-rate lateral irrigation (VRLI) system was developed for site-specific application of water to match field variability. The system consists of solid-state relays controlled by custom software, air-actuated diaphragm valves, a forward speed control system and a GPS receiver. The Clemson VRLI system applies variable-rate water utilizing the nozzle-pulsing technique and variable speed control system. This system could monitor and apply water based on the actual soil moisture content, pan evaporation data, or the U.S. Climate Reference Network (CRN) data. Uniformity tests show that the system is able to control the irrigation rate from 0 to 2.5 cm of irrigation water and can control the forward speed between 145 and 29 m/h. The pulsing technique to deliver variable amounts of irrigation had little adverse effect on system uniformity and nozzle flow rate with an average application error of less than 2%. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Water consumption in agriculture is quickly becoming a concern in the humid Southeast, caused by increased demand and higher frequency and duration of drought. South Carolina, for example, experienced one of its most severe droughts during 1998 to 2002, during which many stream flows reached historic lows, lakes drained below normal levels, and wells had to be deepened (Badr et al., 2004). Greater emphasis on water conservation and efficient application and use of water is thus needed to maximize water use efficiency and enhance sustainability. In the Coastal Plains region in the southeastern U.S., crops are generally produced in fields which are known to have a high degree of variability in soil type, and thus water holding capacity and infiltration rate, topography, and other major factors which affect crop production. In these fields, the ability to turn irrigation water on or off or apply variably to different segments of the field is more efficient than the conventional uniform application. The on/off feature helps eliminate wasting irrigation water on areas of the field
夽 Technical Contribution No. 5232 of the Clemson University Experiment Station. Mention of specific products is for information only and not for the exclusion of others that may be suitable. ∗ Corresponding author at: Department of Agricultural and Biological Engineering, 248 McAdams Hall, Clemson University, Clemson, SC 29634-0312, United States. Tel.: +1 864 656 4046; fax: +1 864 656 0338. E-mail address: [email protected] (Y.J. Han). 0168-1699/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.compag.2009.05.002
that should not be wetted, such as drainage ditches, boggy and low yielding areas, or any non-crop or highly eroded areas. The other advantage of a variable-rate system is to apply different rates of water to different soils to avoid crop water stress due to infrequent application to light textured soils, and to better match soil intake rates in heavier soils. By combining current irrigation systems with sensing equipment and proper water management strategies, a variable-rate irrigation system can apply water to better meet texture and intake variability across the field with the potential to improve water and energy use efficiency and crop yield. Research dealing with variable-rate application of irrigation water has been ongoing for a number of years (McCann and Stark, 1993; King et al., 1995; Evans et al., 1996; Camp et al., 1998; Perry et al., 2002, 2003a). The concept of VRI and its design considerations, economics and environmental benefits have also been explored using field data and simulation modeling (Fraisse et al., 1995; Heermann et al., 1999; Evans and Harting, 1999; Duke et al., 2000; Sadler et al., 2000, 2002; Watkins et al., 2002; Perry et al., 2004; Oliveiria et al., 2005; King et al., 2006). Most past work favored selfpropelled irrigation systems, like center-pivot and lateral-move, due to their widespread availability and adaptability to automation (Sadler et al., 2005). These efforts were independently pursued at first and gradually overlapped as work was publicized. In Fort Collins, CO, Duke et al. (1992) introduced the concept of pulsing and modified a linear-move system to provide variable water and nitrogen application rates. This was accomplished by switching supply solenoids on and off. At about the same time, a microprocessor that controlled individual nozzles, lateral speed, and flow rate of
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the chemical injection pump based on a spatially referenced mapping system was reported in Stark et al. (1993) and later patented by at the University of Idaho (McCann and Stark, 1993) for sitespecific application of water and chemicals through lateral-move and center-pivot irrigation systems. This latter work led to a sitespecific irrigation machine as described in King et al. (1995). A multiple-segment water application system was also developed by Camp et al. (1998) in Florence, SC, and attached to a center-pivot irrigation system to provide variable application depths within each segment at a given speed. Each segment consisted of three parallel manifolds with different nozzle sizes such that they could be operated individually or in various combinations to provide eight application rates at any given tower speed (Omary et al., 1997). The advantage of this system is the ability for variable-rate water application depths to small discrete areas under the center-pivot system as opposed to the much wider wetting patterns produced by commercial sprinklers. The development of a custom control system on a commercially operated center-pivot system that started as early as 1991 (McCann and Stark, 1993), was further pursued at multiple locations, including at Washington State University (Evans et al., 1996; Evans and Harting, 1999) on full and partial commercially operated centerpivot systems. As summarized in Buchleiter et al. (2000), various techniques were used in the above studies to design and control irrigation machines for variable-rate application. Using a modification of the above system, the Precision Ag Team of the University of Georgia at NESPAL (National Environmentally Sound Production Agriculture Laboratory) developed a VRI system for differentially applying center-pivot irrigation water (Perry et al., 2003b). In 2002, test results in three growers’ fields showed a substantial amount of water conservation over 20 million liters (about 40 mm per unit area/year). The NESPAL variable-rate center-pivot system is currently commercially available. However, no commercially available system for lateral-move irrigation system has been developed. Lateral systems are important to farmers in the Southeast. Due to irregular-shaped fields (long and narrow), most of the time it is not feasible to use a center-pivot in this region. Furthermore, lateral systems are important to researchers who wish to lay out rectangular plots, as opposed to the odd-shaped, triangular plots associated with center pivots. 2. Objective The overall objective of this project was to develop and field test equipment and software for variable-rate application of water using a lateral-move irrigation system.
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Fig. 1. The Clemson variable-rate irrigation system.
evenly apart at 3 m (120 in.) and connected to drop-tubing at a height of 2 m (80 in.) above the ground. Each nozzle is equipped with a 140-kPa Nelson pressure regulators (Fig. 2A). Just downstream of the pressure control valve is a Bermad (Anaheim, CA) air-actuated, normally open diaphragm valve (Fig. 2B). This valve is used for cycling sprinklers OFF and ON. Installed on the top of the lateral between the spans is a fivesolenoid valve manifold enclosed in a weatherproof case (Fig. 2C). Each valve is a 3-way, normally closed, 120 V electric solenoid valve manufactured by ASCO (Florham Park, NJ). Eight-conductor, 12 AWG shielded wire was run from the lateral’s transformer to the manifold housing box to supply power to the solenoids. The solenoid valve controls the flow of compressed air to a group of diaphragm valves for cycling purpose. The compressed air is supplied by an air compressor with a 9.5-L reservoir tank mounted on the lateral (Campbell-Hausfield, Fig. 2D). When a solenoid receives a 120-V signal, the valve opens, allowing air to flow into the pneumatic diaphragm valve. As air enters the normally open diaphragm valve, it closes, thus preventing water from flowing through the nozzle. The diaphragm valves are “daisy-chained” together in groups of five using 3 mm diameter neoprene tubing. Therefore, each solenoid controls a bank of five nozzles. The electrical signals, sent to the solenoids to turn the water off, are controlled by a solid-state relay board (SSR-RACK24, Measurement Computing, Middleboro, MA, Fig. 2G) with AC-switch solid-state relays (SSR-OAC-05, Measurement Computing). A lap-
3. Materials and methods 3.1. Clemson variable-rate lateral irrigation design and hardware A variable-rate lateral irrigation (VRLI) system was developed for site-specific application of water by modifying an existing 76-m long Reinke lateral irrigation system with an integrated GPS positioning (Fig. 1). The VRLI system uses the pulse system described by Perry et al. (2003b), which cycles individual sprinklers or groups of sprinklers OFF and ON, and a speed control system which varies forward travel speed to achieve desired irrigation rates within management zones. In doing so, the system moves quickly over wet spots and slows down over dry spots. The VRLI system consists of 25 quick-change spinner nozzles, which were grouped into 5 management zones (5 sprinklers in each zone) for research purposes. The system controls each bank of five nozzles in each of the five management zones. The 25 Nelson #36 quick-change spinner nozzles (Walla Walla, WA) were spaced
Fig. 2. Variable-rate lateral control system (A: pressure control valve; B: diaphragm valve; C: solenoid; D: air compressor; E: GPS receiver; F: control PC; G: solid-state relay board; H: base radio; and I: wireless Internet).
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Fig. 3. Gro-Point soil moisture sensor (inset) and radio transmitter.
top computer (Fig. 2F), equipped with a data acquisition and control adaptor (MiniLab-1008, Measurement Computing), is used to control 24 lines of digital output to the solid-state relay board. A digital I/O card (PC-Card D24/CTR3, Measurement Computing) is also compatible with this system, and can replace the MiniLab-1008. The forward driving motor is connected to one of the solid-state relays, and controlled by turning the driving motor ON or OFF between 10% and 100% duty cycle. A GPS antenna was installed on top of the lateral (Fig. 2E) and connected to a receiver (AgGPS, Trimble Navigation Limited, Sunnydale, CA) mounted inside the weatherproof box. At the pump house, a variable frequency drive (Zentac America, Madison, CT) was installed to slow down the electrical motor as the downstream system demand for water decreased due to nozzles shutting off. The variable frequency drive operates in the range from 60 Hz at full capacity to about 40 Hz. When the pump motor turns at a rate below 40 Hz, it was programmed to automatically shut down the motor to prevent overheating of the shaft and bearings. A highpressure cut-off switch was also installed at the pump to shut off the motor when line pressure exceeded 550 kPa. It was noted that the variable frequency drive can only respond to average flow rate conditions and not instantaneous flow rate variations. 3.2. Communication and data acquisition systems The Clemson VRLI system could monitor and apply water based on the actual soil moisture content, pan evaporation data, or the U.S. Climate Reference Network (CRN) data. Communication systems had to be developed in order to transmit sensor data to the computer. Fig. 3 shows a Gro-Point soil moisture sensor (Environmental Sensors Inc., Sidney, BC, Canada) and radio transmitter in the field. Ten Gro-Point moisture sensors were installed at two different depths (20 and 35 cm) at five locations in the test field. For each location, a radio transmitter was mounted on a 2.4-m fiberglass pole which transmits moisture data from two sensors to the control–data-acquisition (CDA) system. A 6-V solar power panel, also mounted on the pole, provides power to charge the transmitter’s battery. The pole is anchored between rows and is able to be removed easily when necessary. Fig. 4 shows a standard pan evaporation system that was modified so that real-time evaporation data can be transmitted to the CDA system using radio signals. A 1.2-m diameter by 25 cm deep standard evaporation pan rests on a 400-kg load cell (LC101). The signal is sent to a signal conditioner (DMD-465) that was calibrated to the depth of water in the pan. A radio transmitter sends the signal to the base station. The irrigation intervals can be determined
Fig. 4. Evaporation pan load cell (inset, upper-left) and signal conditioner (inset, lower-left).
based on pan evaporation data and crop coefficient values for days after planting using water balance method explained by Harrison and Tyson (1993). A base-station radio (Environmental Sensors Inc.) was installed on the top of the lateral (Fig. 2H) to receive the signals from the soil moisture sensors and pan evaporation system. Using Aqualink software (V5.0.4.31, Environmental Sensors Inc.), volumetric soil moisture content from each moisture sensor and voltage output from the evaporation pan are recorded. Moisture sensors were used to determine depleted soil moisture by converting sensor readings to volumetric soil moisture content (VSMC) and subtracting it from the field capacity for each soil layer. Irrigation depth was calculated by adding the depleted water in both soil layers. Wireless Internet is installed on the lateral system. A Cisco 340 wireless bridge inside the weatherproof box is used as a wireless link between a Cisco Aironet YAGI directional wireless antenna with 13.5 dB gain installed on a 28-m tower near the main office building and an omni-directional 12 dB gain unit mounted on top of the lateral (Fig. 2I). The Internet is used to download data from a nearby NOAA Weather Station for use in irrigation scheduling. The reference evapotranspiration (ET0 ) was estimated using the Jensen–Haise equation (Jensen et al., 1990) and NWS data. The U.S. mean daily solar radiation, average daily temperature, and rainfall data were downloaded from the NOAA WebPages and used in calculation of the (ET0 ). The crop water use (ETc) for irrigation scheduling was calculated by multiplying the reference evapotranspiration (ET0 ) by a crop coefficient (Kc) for cotton. The crop coefficient curve for cotton is given by Harrison and Tyson (1993). 3.3. Clemson variable-rate lateral irrigation control software A set of custom software was developed to support Clemson Lateral Irrigation System. The first is “Field Configuration Utility” software that collects the field information, including the length and width of the field, its GPS coordinates and the orientation of the lateral, number of irrigation control sections and zones. An example field information form is shown in Fig. 5. The Field is divided into a number of “Sections” and “Zones” in which the irrigation rates could be controlled. The “Control Section” follows the direction of the Lateral Guide (travel path) and one could have as many sections as practically possible. Since the irrigation control program will be working on a 60-s cycle, however, it is recommended to select a section length long enough to be covered by lateral in at least 2 min. The “Section Length” can be fixed or variable. If one selects the Variable Length option, the cumulative
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Fig. 6. Example screen of irrigation depth map.
Fig. 5. Example of Clemson Lateral Field Configuration Utility.
sum of all variable section lengths should match the Field Length. The control system can turn a bank of nozzles on/off in each “Control Zone.” The number of Control Zones is set by the hardware, and should match the number of relays (solenoid valves) installed on the lateral. The Zone Widths, either fixed or variable, also depend on how the boom and nozzles are set up. With up to 24 digital control lines, Clemson lateral hardware and software can support up to 23 Control Zones and a forward drive control. The Relay Number for the forward drive control is set by the hardware installation. The Forward Speed at 25.4 mm (1.0 in.) of irrigation depth also depends on the lateral hardware and described in % speed setting. The Irrigation Control Program will use these information to calculate the speed of the lateral and to send control signals to the forward driving motor. The Time Delay between Control Zones is implemented to prevent a “water-hammer” effect that may happen when many nozzles are turned on/off at the same time when the lateral goes into a new Control Section. This function can be turned off, if necessary, by specifying 0 s to Time Delay between Control Zones. Most of the information shown in Fig. 5 is field- and equipment-dependent, and may not need to be changed once entered. The irrigation rate information will be entered on the second part of the Field Configuration Utility. A site-specific irrigation depth map can be graphically prescribed. Fig. 6 shows 12 Control Zones along the length of the lateral system and 15 Sections along the travel path. An irrigation depth can be set by clicking one of the rate buttons on the left and clicking anywhere inside the field to apply the selected rate to the zone. One may also click and drag the mouse pointer to paint more than one square at a time. A custom rate can be set by right-clicking any square and entering an irrigation depth. The irrigation map can also be imported from or exported to an Excel spreadsheet. Fig. 7 shows the second software, “Clemson Lateral Irrigation Control” (CLIC), which takes the irrigation application map prescribed by the “Field Configuration Utility” and actually controls the irrigation system. The CLIC program is capable of controlling up to 23 individual control zones, and the forward motion of the lateral. The variable-rate speed control assures that the lateral moves
quickly over wet spots and slows down over dry spots. Using the position signal from the DGPS, the speed of the lateral for the section is calculated based on the highest irrigation depth in the section so that nozzles in a zone with the highest depth will remain ON all the time. This assures that at least one bank of nozzles is on at all times, preventing a high-pressure cut-off at the pump house. In the example in Fig. 7, Zone 5 has the highest application depth of 25.4 mm (1.0 in.), and the forward speed is set to 24% so that “always-on” nozzle can deliver this application depth. The CLIC program then calculates the nozzle on/off time for each zone as the fraction of the highest irrigation depth in a 60-s on/off cycle. For example, since Zones 1, 2, and 3 all have 10.2 mm (0.40 in.) of irrigation depth, nozzles in these zones will be turned on for 24 s and off for 36 s. The colored arcs shown in the figure signify the remaining on/off times, where the full circle represents 60 s. The reason that the sizes of the arcs in Zones 1, 2, and 3 are different is because of the 2.0 s time delay between Control Zones, as speci-
Fig. 7. Example of Clemson lateral irrigation control program.
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Fig. 9. Effects of pulsing on irrigation rate (100% = nozzles are ON all the time; 75% = ON for 45 s and OFF for 15 s; 50% = ON for 30 s and OFF for 30 s; 25% = ON for 15 s and OFF for 45 s).
cation rate error was less than 2% for all rates. There was a strong correlation between the nozzle theoretical flow and measured flow (R2 = 0.9991). The nozzle output flow could be calculated by the following equation: Q = 35.688P + 2.8951 Fig. 8. Example of the simulated GPS Demo program.
fied in the Field Configuration Utility. The whole control process of determining the position, forward speed and controlling individual nozzles is repeated every 500 ms. This means that even at full forward speed, the system can control the irrigation rate every 2 cm of forward movement. Another useful feature of the Clemson Lateral Irrigation System is its Demo/Simulation capability. A CLIC Demo program has the same user interface as the CLIC program, without actually controlling the hardware. This feature can be used to easily demonstrate the look-and-feel of the CLIC program to consultants and farmers without being tied to the irrigation system. A custom utility program shown in Fig. 8 can send a simulated GPS coordinate of any position in the field to the CLIC Demo program by using two serial ports connected with a null-modem cable. It can send a static coordinate chosen manually, or advance the coordinate automatically to simulate a continuous lateral movement in the field. The CLIC Demo program will respond to the received coordinate and simulate the irrigation control operation. Researchers can also use this capability to simulate what-if scenarios of an irrigation session and observe what would happen in the field without leaving their offices. The CLIC and CLIC Demo program keep detailed log files of every control functions during its operation, a useful feature for system diagnostics/repair. 4. Irrigation system performance test Tests were conducted to ensure that the nozzle-pulsing technique produces the desired amount of irrigation water. Tests were run for 100%, 75%, 50%, and 25% nozzle ON times based on a 60-s on/off cycle. For example, at 25% rate, nozzles would pulse 15 s ON and 45 s OFF. As the nozzles were pulsed on and off, a bucket was used to catch the water for a period of 2 min. Flow rates were calculated for each of the nozzle ON time rates. Fig. 9 shows individual nozzle output at different pulsing rates. The nozzles produced an average flow of 38.2, 28.5, 18.7, and 8.7 L/min for the 100%, 75%, 50%, and 25% of nozzle ON time, respectively. The average water appli-
where P is the nozzle on time (%) and Q is the nozzle discharge (L/m). The Clemson VRLI system was tested in a 2-ha field at the Edisto Research and Education Center near Blackville, SC. The main purpose of the test was to evaluate performance of the hardware and software under actual field conditions. In addition, the system was used to determine the optimum irrigation scheduling method for cotton production utilizing site-specific irrigation management (Khalilian et al., 2007). The results during a 2-year test period showed that communication from the moisture sensors and the evaporation pan worked as expected. Internet capability on the system allowed for weather data to be downloaded to the computer on the lateral. The computer software was able to pulse the water on and off for any given application rate in each respective plot. A uniformity test of the system was conducted following ASAE Standard S436.1 (ASAE Standards, 2003). Plastic cups (84 mm diameter and 124 mm height) were placed in a grid and spaced at 0.75 m apart along the span of the lateral. Four rows of 17 cups were spaced apart at 1.5 m. The coefficient of uniformity (CU) was calculated by the Christiansen formula for four different irrigation application depths. The CU values were 94.0, 94.8, 91.7, and 79.5 for the four depths of 25, 19, 13, and 6 mm, respectively. Except for the 6 mm test, which was affected by high wind, the results were similar to those reported in Perry et al. (2004) who showed high CU values with a slight degradation as the sprinkler cycling rate decreased. The sprinkler cycling had no discernable impact on overall application uniformity. The forward speed control was able to adjust the lateral’s speed from 145 m/h at 100% duty cycle to 29.1 m/h at 20% duty cycle. Energy savings resulting from pumping less water to the irrigation system was also studied by comparing the power drawn by the pump to the percent flow rate. The power consumption was measured using a PMT AC Motor/Load Surveyor (Esterline-Angus). When using the variable speed drive, the pump used 27% less power when pumping at 80% flow rate to the lateral; it uses 42% less power when pumping at 60% flow rate; and it consumed 52% less power when pumping at 40% flow rate. Using the calculated power consumption values, the power savings were 19%, 39%, and 59% at of 80%, 60%, and 40% flow rates, respectively.
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5. Summary and conclusions A variable-rate lateral irrigation system was developed and tested. The system consists of solid-state relays controlled by custom software, air-actuated diaphragm valves, and a forward speed control system. The system is capable of controlling five management zones of five nozzles per each zone to produce a variable amount of water application using the pulsing method. The accompanying software can control up to 23 Control Zones and the forward speed of the lateral. This system could monitor and apply water based on the actual soil moisture content, pan evaporation data, or the U.S. Climate Reference Network (CRN) data. Uniformity tests showed that the system is able to control the irrigation rate from 0 to 25 mm (1 in.) of irrigation water and can control the forward speed between 145 and 29 m/h. The variable speed control system allows the irrigation system to move faster over wet zones that require a lighter irrigation amount, and slower over zones requiring a heavier irrigation amount. From nozzle-pulsing tests, it was found that the average water application error was less than 2%. The pulsing technique to deliver variable amounts of irrigation had little adverse effect on system uniformity and nozzle flow rate. The computer software was able to pulse the water on and off for any given application rate in each respective plot. This article provides sufficient detail for interested readers to duplicate and/or modify the system to fit their specific needs. Compared to the conventional uniform irrigation application, the practice of variable-rate irrigation requires a higher level of management, advanced system hardware and software, and an application map based on soil and/or crop water stress variability. Obviously, adoption by farmers will be enhanced if costs associated with these additions are offset by increased profit, crop quality, and environmental benefits. Thus, economic analysis, not performed herein, is needed to gauge potential adoptability. The immediate usefulness of the system is currently recognized at Clemson’s Experiment Station, Edisto Research and Education Center, for research, education, training, and demonstration of the impact of variablerate irrigation on crop growth. Acknowledgements The authors acknowledge the support of Cotton Incorporated and the South Carolina Cotton Grower’s Association. References ASAE Standards, 2003. S436.1. Test Procedure for Determining the Uniformity of Water Distribution on Center Pivot and Lateral Mover Irrigation Machines Equipped with Spray or Sprinkler Nozzles. ASAE, St. Joseph, MI. Badr, W., Wachob, A., Gellici, J.A., 2004. South Carolina Water Plan, second edition. South Carolina Department of Natural Resources, Columbia, SC, 120 p. Buchleiter, G.W., Camp, C.R., Evans, R.G., King, B.A., 2000. Technologies for variable water application with sprinklers. In: Evans, R.G., Benham, B.L., Trooien, T.P. (Eds.), Proceedings of the 4th Decennial National Irrigation Symposium. American Society of Agricultural Engineers, St. Joseph, MI. Camp, C.R., Sadler, E.J., Evans, D.E., Usrey, L.J., Omary, M., 1998. Modified center pivot system for precision management of water and nutrients. Appl. Eng. Agric. 14 (1), 23–31.
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Computers and Electronics in Agriculture journal homepage: www.elsevier.com/locate/compag
Development of Clemson variable-rate lateral irrigation system夽 Young J. Han ∗ , Ahmad Khalilian, Tom O. Owino, Hamid J. Farahani, Sam Moore Department of Agricultural and Biological Engineering, Clemson University, Clemson, SC 29634-0312, United States
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Article history: Received 22 September 2008 Received in revised form 16 March 2009 Accepted 4 May 2009 Keywords: Irrigation Precision agriculture Variable-rate irrigation Instrumentation Lateral-move
a b s t r a c t Crops in the Southern United States are generally produced in fields which are known to have a high degree of variability in soil type, water holding capacity, infiltration rates, and other major factors which affect crop production. In these fields, the ability to turn irrigation water on or off or apply variably to different segments of the field is advantageous over the conventional uniform application. A variable-rate lateral irrigation (VRLI) system was developed for site-specific application of water to match field variability. The system consists of solid-state relays controlled by custom software, air-actuated diaphragm valves, a forward speed control system and a GPS receiver. The Clemson VRLI system applies variable-rate water utilizing the nozzle-pulsing technique and variable speed control system. This system could monitor and apply water based on the actual soil moisture content, pan evaporation data, or the U.S. Climate Reference Network (CRN) data. Uniformity tests show that the system is able to control the irrigation rate from 0 to 2.5 cm of irrigation water and can control the forward speed between 145 and 29 m/h. The pulsing technique to deliver variable amounts of irrigation had little adverse effect on system uniformity and nozzle flow rate with an average application error of less than 2%. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Water consumption in agriculture is quickly becoming a concern in the humid Southeast, caused by increased demand and higher frequency and duration of drought. South Carolina, for example, experienced one of its most severe droughts during 1998 to 2002, during which many stream flows reached historic lows, lakes drained below normal levels, and wells had to be deepened (Badr et al., 2004). Greater emphasis on water conservation and efficient application and use of water is thus needed to maximize water use efficiency and enhance sustainability. In the Coastal Plains region in the southeastern U.S., crops are generally produced in fields which are known to have a high degree of variability in soil type, and thus water holding capacity and infiltration rate, topography, and other major factors which affect crop production. In these fields, the ability to turn irrigation water on or off or apply variably to different segments of the field is more efficient than the conventional uniform application. The on/off feature helps eliminate wasting irrigation water on areas of the field
夽 Technical Contribution No. 5232 of the Clemson University Experiment Station. Mention of specific products is for information only and not for the exclusion of others that may be suitable. ∗ Corresponding author at: Department of Agricultural and Biological Engineering, 248 McAdams Hall, Clemson University, Clemson, SC 29634-0312, United States. Tel.: +1 864 656 4046; fax: +1 864 656 0338. E-mail address: [email protected] (Y.J. Han). 0168-1699/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.compag.2009.05.002
that should not be wetted, such as drainage ditches, boggy and low yielding areas, or any non-crop or highly eroded areas. The other advantage of a variable-rate system is to apply different rates of water to different soils to avoid crop water stress due to infrequent application to light textured soils, and to better match soil intake rates in heavier soils. By combining current irrigation systems with sensing equipment and proper water management strategies, a variable-rate irrigation system can apply water to better meet texture and intake variability across the field with the potential to improve water and energy use efficiency and crop yield. Research dealing with variable-rate application of irrigation water has been ongoing for a number of years (McCann and Stark, 1993; King et al., 1995; Evans et al., 1996; Camp et al., 1998; Perry et al., 2002, 2003a). The concept of VRI and its design considerations, economics and environmental benefits have also been explored using field data and simulation modeling (Fraisse et al., 1995; Heermann et al., 1999; Evans and Harting, 1999; Duke et al., 2000; Sadler et al., 2000, 2002; Watkins et al., 2002; Perry et al., 2004; Oliveiria et al., 2005; King et al., 2006). Most past work favored selfpropelled irrigation systems, like center-pivot and lateral-move, due to their widespread availability and adaptability to automation (Sadler et al., 2005). These efforts were independently pursued at first and gradually overlapped as work was publicized. In Fort Collins, CO, Duke et al. (1992) introduced the concept of pulsing and modified a linear-move system to provide variable water and nitrogen application rates. This was accomplished by switching supply solenoids on and off. At about the same time, a microprocessor that controlled individual nozzles, lateral speed, and flow rate of
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the chemical injection pump based on a spatially referenced mapping system was reported in Stark et al. (1993) and later patented by at the University of Idaho (McCann and Stark, 1993) for sitespecific application of water and chemicals through lateral-move and center-pivot irrigation systems. This latter work led to a sitespecific irrigation machine as described in King et al. (1995). A multiple-segment water application system was also developed by Camp et al. (1998) in Florence, SC, and attached to a center-pivot irrigation system to provide variable application depths within each segment at a given speed. Each segment consisted of three parallel manifolds with different nozzle sizes such that they could be operated individually or in various combinations to provide eight application rates at any given tower speed (Omary et al., 1997). The advantage of this system is the ability for variable-rate water application depths to small discrete areas under the center-pivot system as opposed to the much wider wetting patterns produced by commercial sprinklers. The development of a custom control system on a commercially operated center-pivot system that started as early as 1991 (McCann and Stark, 1993), was further pursued at multiple locations, including at Washington State University (Evans et al., 1996; Evans and Harting, 1999) on full and partial commercially operated centerpivot systems. As summarized in Buchleiter et al. (2000), various techniques were used in the above studies to design and control irrigation machines for variable-rate application. Using a modification of the above system, the Precision Ag Team of the University of Georgia at NESPAL (National Environmentally Sound Production Agriculture Laboratory) developed a VRI system for differentially applying center-pivot irrigation water (Perry et al., 2003b). In 2002, test results in three growers’ fields showed a substantial amount of water conservation over 20 million liters (about 40 mm per unit area/year). The NESPAL variable-rate center-pivot system is currently commercially available. However, no commercially available system for lateral-move irrigation system has been developed. Lateral systems are important to farmers in the Southeast. Due to irregular-shaped fields (long and narrow), most of the time it is not feasible to use a center-pivot in this region. Furthermore, lateral systems are important to researchers who wish to lay out rectangular plots, as opposed to the odd-shaped, triangular plots associated with center pivots. 2. Objective The overall objective of this project was to develop and field test equipment and software for variable-rate application of water using a lateral-move irrigation system.
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Fig. 1. The Clemson variable-rate irrigation system.
evenly apart at 3 m (120 in.) and connected to drop-tubing at a height of 2 m (80 in.) above the ground. Each nozzle is equipped with a 140-kPa Nelson pressure regulators (Fig. 2A). Just downstream of the pressure control valve is a Bermad (Anaheim, CA) air-actuated, normally open diaphragm valve (Fig. 2B). This valve is used for cycling sprinklers OFF and ON. Installed on the top of the lateral between the spans is a fivesolenoid valve manifold enclosed in a weatherproof case (Fig. 2C). Each valve is a 3-way, normally closed, 120 V electric solenoid valve manufactured by ASCO (Florham Park, NJ). Eight-conductor, 12 AWG shielded wire was run from the lateral’s transformer to the manifold housing box to supply power to the solenoids. The solenoid valve controls the flow of compressed air to a group of diaphragm valves for cycling purpose. The compressed air is supplied by an air compressor with a 9.5-L reservoir tank mounted on the lateral (Campbell-Hausfield, Fig. 2D). When a solenoid receives a 120-V signal, the valve opens, allowing air to flow into the pneumatic diaphragm valve. As air enters the normally open diaphragm valve, it closes, thus preventing water from flowing through the nozzle. The diaphragm valves are “daisy-chained” together in groups of five using 3 mm diameter neoprene tubing. Therefore, each solenoid controls a bank of five nozzles. The electrical signals, sent to the solenoids to turn the water off, are controlled by a solid-state relay board (SSR-RACK24, Measurement Computing, Middleboro, MA, Fig. 2G) with AC-switch solid-state relays (SSR-OAC-05, Measurement Computing). A lap-
3. Materials and methods 3.1. Clemson variable-rate lateral irrigation design and hardware A variable-rate lateral irrigation (VRLI) system was developed for site-specific application of water by modifying an existing 76-m long Reinke lateral irrigation system with an integrated GPS positioning (Fig. 1). The VRLI system uses the pulse system described by Perry et al. (2003b), which cycles individual sprinklers or groups of sprinklers OFF and ON, and a speed control system which varies forward travel speed to achieve desired irrigation rates within management zones. In doing so, the system moves quickly over wet spots and slows down over dry spots. The VRLI system consists of 25 quick-change spinner nozzles, which were grouped into 5 management zones (5 sprinklers in each zone) for research purposes. The system controls each bank of five nozzles in each of the five management zones. The 25 Nelson #36 quick-change spinner nozzles (Walla Walla, WA) were spaced
Fig. 2. Variable-rate lateral control system (A: pressure control valve; B: diaphragm valve; C: solenoid; D: air compressor; E: GPS receiver; F: control PC; G: solid-state relay board; H: base radio; and I: wireless Internet).
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Fig. 3. Gro-Point soil moisture sensor (inset) and radio transmitter.
top computer (Fig. 2F), equipped with a data acquisition and control adaptor (MiniLab-1008, Measurement Computing), is used to control 24 lines of digital output to the solid-state relay board. A digital I/O card (PC-Card D24/CTR3, Measurement Computing) is also compatible with this system, and can replace the MiniLab-1008. The forward driving motor is connected to one of the solid-state relays, and controlled by turning the driving motor ON or OFF between 10% and 100% duty cycle. A GPS antenna was installed on top of the lateral (Fig. 2E) and connected to a receiver (AgGPS, Trimble Navigation Limited, Sunnydale, CA) mounted inside the weatherproof box. At the pump house, a variable frequency drive (Zentac America, Madison, CT) was installed to slow down the electrical motor as the downstream system demand for water decreased due to nozzles shutting off. The variable frequency drive operates in the range from 60 Hz at full capacity to about 40 Hz. When the pump motor turns at a rate below 40 Hz, it was programmed to automatically shut down the motor to prevent overheating of the shaft and bearings. A highpressure cut-off switch was also installed at the pump to shut off the motor when line pressure exceeded 550 kPa. It was noted that the variable frequency drive can only respond to average flow rate conditions and not instantaneous flow rate variations. 3.2. Communication and data acquisition systems The Clemson VRLI system could monitor and apply water based on the actual soil moisture content, pan evaporation data, or the U.S. Climate Reference Network (CRN) data. Communication systems had to be developed in order to transmit sensor data to the computer. Fig. 3 shows a Gro-Point soil moisture sensor (Environmental Sensors Inc., Sidney, BC, Canada) and radio transmitter in the field. Ten Gro-Point moisture sensors were installed at two different depths (20 and 35 cm) at five locations in the test field. For each location, a radio transmitter was mounted on a 2.4-m fiberglass pole which transmits moisture data from two sensors to the control–data-acquisition (CDA) system. A 6-V solar power panel, also mounted on the pole, provides power to charge the transmitter’s battery. The pole is anchored between rows and is able to be removed easily when necessary. Fig. 4 shows a standard pan evaporation system that was modified so that real-time evaporation data can be transmitted to the CDA system using radio signals. A 1.2-m diameter by 25 cm deep standard evaporation pan rests on a 400-kg load cell (LC101). The signal is sent to a signal conditioner (DMD-465) that was calibrated to the depth of water in the pan. A radio transmitter sends the signal to the base station. The irrigation intervals can be determined
Fig. 4. Evaporation pan load cell (inset, upper-left) and signal conditioner (inset, lower-left).
based on pan evaporation data and crop coefficient values for days after planting using water balance method explained by Harrison and Tyson (1993). A base-station radio (Environmental Sensors Inc.) was installed on the top of the lateral (Fig. 2H) to receive the signals from the soil moisture sensors and pan evaporation system. Using Aqualink software (V5.0.4.31, Environmental Sensors Inc.), volumetric soil moisture content from each moisture sensor and voltage output from the evaporation pan are recorded. Moisture sensors were used to determine depleted soil moisture by converting sensor readings to volumetric soil moisture content (VSMC) and subtracting it from the field capacity for each soil layer. Irrigation depth was calculated by adding the depleted water in both soil layers. Wireless Internet is installed on the lateral system. A Cisco 340 wireless bridge inside the weatherproof box is used as a wireless link between a Cisco Aironet YAGI directional wireless antenna with 13.5 dB gain installed on a 28-m tower near the main office building and an omni-directional 12 dB gain unit mounted on top of the lateral (Fig. 2I). The Internet is used to download data from a nearby NOAA Weather Station for use in irrigation scheduling. The reference evapotranspiration (ET0 ) was estimated using the Jensen–Haise equation (Jensen et al., 1990) and NWS data. The U.S. mean daily solar radiation, average daily temperature, and rainfall data were downloaded from the NOAA WebPages and used in calculation of the (ET0 ). The crop water use (ETc) for irrigation scheduling was calculated by multiplying the reference evapotranspiration (ET0 ) by a crop coefficient (Kc) for cotton. The crop coefficient curve for cotton is given by Harrison and Tyson (1993). 3.3. Clemson variable-rate lateral irrigation control software A set of custom software was developed to support Clemson Lateral Irrigation System. The first is “Field Configuration Utility” software that collects the field information, including the length and width of the field, its GPS coordinates and the orientation of the lateral, number of irrigation control sections and zones. An example field information form is shown in Fig. 5. The Field is divided into a number of “Sections” and “Zones” in which the irrigation rates could be controlled. The “Control Section” follows the direction of the Lateral Guide (travel path) and one could have as many sections as practically possible. Since the irrigation control program will be working on a 60-s cycle, however, it is recommended to select a section length long enough to be covered by lateral in at least 2 min. The “Section Length” can be fixed or variable. If one selects the Variable Length option, the cumulative
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Fig. 6. Example screen of irrigation depth map.
Fig. 5. Example of Clemson Lateral Field Configuration Utility.
sum of all variable section lengths should match the Field Length. The control system can turn a bank of nozzles on/off in each “Control Zone.” The number of Control Zones is set by the hardware, and should match the number of relays (solenoid valves) installed on the lateral. The Zone Widths, either fixed or variable, also depend on how the boom and nozzles are set up. With up to 24 digital control lines, Clemson lateral hardware and software can support up to 23 Control Zones and a forward drive control. The Relay Number for the forward drive control is set by the hardware installation. The Forward Speed at 25.4 mm (1.0 in.) of irrigation depth also depends on the lateral hardware and described in % speed setting. The Irrigation Control Program will use these information to calculate the speed of the lateral and to send control signals to the forward driving motor. The Time Delay between Control Zones is implemented to prevent a “water-hammer” effect that may happen when many nozzles are turned on/off at the same time when the lateral goes into a new Control Section. This function can be turned off, if necessary, by specifying 0 s to Time Delay between Control Zones. Most of the information shown in Fig. 5 is field- and equipment-dependent, and may not need to be changed once entered. The irrigation rate information will be entered on the second part of the Field Configuration Utility. A site-specific irrigation depth map can be graphically prescribed. Fig. 6 shows 12 Control Zones along the length of the lateral system and 15 Sections along the travel path. An irrigation depth can be set by clicking one of the rate buttons on the left and clicking anywhere inside the field to apply the selected rate to the zone. One may also click and drag the mouse pointer to paint more than one square at a time. A custom rate can be set by right-clicking any square and entering an irrigation depth. The irrigation map can also be imported from or exported to an Excel spreadsheet. Fig. 7 shows the second software, “Clemson Lateral Irrigation Control” (CLIC), which takes the irrigation application map prescribed by the “Field Configuration Utility” and actually controls the irrigation system. The CLIC program is capable of controlling up to 23 individual control zones, and the forward motion of the lateral. The variable-rate speed control assures that the lateral moves
quickly over wet spots and slows down over dry spots. Using the position signal from the DGPS, the speed of the lateral for the section is calculated based on the highest irrigation depth in the section so that nozzles in a zone with the highest depth will remain ON all the time. This assures that at least one bank of nozzles is on at all times, preventing a high-pressure cut-off at the pump house. In the example in Fig. 7, Zone 5 has the highest application depth of 25.4 mm (1.0 in.), and the forward speed is set to 24% so that “always-on” nozzle can deliver this application depth. The CLIC program then calculates the nozzle on/off time for each zone as the fraction of the highest irrigation depth in a 60-s on/off cycle. For example, since Zones 1, 2, and 3 all have 10.2 mm (0.40 in.) of irrigation depth, nozzles in these zones will be turned on for 24 s and off for 36 s. The colored arcs shown in the figure signify the remaining on/off times, where the full circle represents 60 s. The reason that the sizes of the arcs in Zones 1, 2, and 3 are different is because of the 2.0 s time delay between Control Zones, as speci-
Fig. 7. Example of Clemson lateral irrigation control program.
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Fig. 9. Effects of pulsing on irrigation rate (100% = nozzles are ON all the time; 75% = ON for 45 s and OFF for 15 s; 50% = ON for 30 s and OFF for 30 s; 25% = ON for 15 s and OFF for 45 s).
cation rate error was less than 2% for all rates. There was a strong correlation between the nozzle theoretical flow and measured flow (R2 = 0.9991). The nozzle output flow could be calculated by the following equation: Q = 35.688P + 2.8951 Fig. 8. Example of the simulated GPS Demo program.
fied in the Field Configuration Utility. The whole control process of determining the position, forward speed and controlling individual nozzles is repeated every 500 ms. This means that even at full forward speed, the system can control the irrigation rate every 2 cm of forward movement. Another useful feature of the Clemson Lateral Irrigation System is its Demo/Simulation capability. A CLIC Demo program has the same user interface as the CLIC program, without actually controlling the hardware. This feature can be used to easily demonstrate the look-and-feel of the CLIC program to consultants and farmers without being tied to the irrigation system. A custom utility program shown in Fig. 8 can send a simulated GPS coordinate of any position in the field to the CLIC Demo program by using two serial ports connected with a null-modem cable. It can send a static coordinate chosen manually, or advance the coordinate automatically to simulate a continuous lateral movement in the field. The CLIC Demo program will respond to the received coordinate and simulate the irrigation control operation. Researchers can also use this capability to simulate what-if scenarios of an irrigation session and observe what would happen in the field without leaving their offices. The CLIC and CLIC Demo program keep detailed log files of every control functions during its operation, a useful feature for system diagnostics/repair. 4. Irrigation system performance test Tests were conducted to ensure that the nozzle-pulsing technique produces the desired amount of irrigation water. Tests were run for 100%, 75%, 50%, and 25% nozzle ON times based on a 60-s on/off cycle. For example, at 25% rate, nozzles would pulse 15 s ON and 45 s OFF. As the nozzles were pulsed on and off, a bucket was used to catch the water for a period of 2 min. Flow rates were calculated for each of the nozzle ON time rates. Fig. 9 shows individual nozzle output at different pulsing rates. The nozzles produced an average flow of 38.2, 28.5, 18.7, and 8.7 L/min for the 100%, 75%, 50%, and 25% of nozzle ON time, respectively. The average water appli-
where P is the nozzle on time (%) and Q is the nozzle discharge (L/m). The Clemson VRLI system was tested in a 2-ha field at the Edisto Research and Education Center near Blackville, SC. The main purpose of the test was to evaluate performance of the hardware and software under actual field conditions. In addition, the system was used to determine the optimum irrigation scheduling method for cotton production utilizing site-specific irrigation management (Khalilian et al., 2007). The results during a 2-year test period showed that communication from the moisture sensors and the evaporation pan worked as expected. Internet capability on the system allowed for weather data to be downloaded to the computer on the lateral. The computer software was able to pulse the water on and off for any given application rate in each respective plot. A uniformity test of the system was conducted following ASAE Standard S436.1 (ASAE Standards, 2003). Plastic cups (84 mm diameter and 124 mm height) were placed in a grid and spaced at 0.75 m apart along the span of the lateral. Four rows of 17 cups were spaced apart at 1.5 m. The coefficient of uniformity (CU) was calculated by the Christiansen formula for four different irrigation application depths. The CU values were 94.0, 94.8, 91.7, and 79.5 for the four depths of 25, 19, 13, and 6 mm, respectively. Except for the 6 mm test, which was affected by high wind, the results were similar to those reported in Perry et al. (2004) who showed high CU values with a slight degradation as the sprinkler cycling rate decreased. The sprinkler cycling had no discernable impact on overall application uniformity. The forward speed control was able to adjust the lateral’s speed from 145 m/h at 100% duty cycle to 29.1 m/h at 20% duty cycle. Energy savings resulting from pumping less water to the irrigation system was also studied by comparing the power drawn by the pump to the percent flow rate. The power consumption was measured using a PMT AC Motor/Load Surveyor (Esterline-Angus). When using the variable speed drive, the pump used 27% less power when pumping at 80% flow rate to the lateral; it uses 42% less power when pumping at 60% flow rate; and it consumed 52% less power when pumping at 40% flow rate. Using the calculated power consumption values, the power savings were 19%, 39%, and 59% at of 80%, 60%, and 40% flow rates, respectively.
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5. Summary and conclusions A variable-rate lateral irrigation system was developed and tested. The system consists of solid-state relays controlled by custom software, air-actuated diaphragm valves, and a forward speed control system. The system is capable of controlling five management zones of five nozzles per each zone to produce a variable amount of water application using the pulsing method. The accompanying software can control up to 23 Control Zones and the forward speed of the lateral. This system could monitor and apply water based on the actual soil moisture content, pan evaporation data, or the U.S. Climate Reference Network (CRN) data. Uniformity tests showed that the system is able to control the irrigation rate from 0 to 25 mm (1 in.) of irrigation water and can control the forward speed between 145 and 29 m/h. The variable speed control system allows the irrigation system to move faster over wet zones that require a lighter irrigation amount, and slower over zones requiring a heavier irrigation amount. From nozzle-pulsing tests, it was found that the average water application error was less than 2%. The pulsing technique to deliver variable amounts of irrigation had little adverse effect on system uniformity and nozzle flow rate. The computer software was able to pulse the water on and off for any given application rate in each respective plot. This article provides sufficient detail for interested readers to duplicate and/or modify the system to fit their specific needs. Compared to the conventional uniform irrigation application, the practice of variable-rate irrigation requires a higher level of management, advanced system hardware and software, and an application map based on soil and/or crop water stress variability. Obviously, adoption by farmers will be enhanced if costs associated with these additions are offset by increased profit, crop quality, and environmental benefits. Thus, economic analysis, not performed herein, is needed to gauge potential adoptability. The immediate usefulness of the system is currently recognized at Clemson’s Experiment Station, Edisto Research and Education Center, for research, education, training, and demonstration of the impact of variablerate irrigation on crop growth. Acknowledgements The authors acknowledge the support of Cotton Incorporated and the South Carolina Cotton Grower’s Association. References ASAE Standards, 2003. S436.1. Test Procedure for Determining the Uniformity of Water Distribution on Center Pivot and Lateral Mover Irrigation Machines Equipped with Spray or Sprinkler Nozzles. ASAE, St. Joseph, MI. Badr, W., Wachob, A., Gellici, J.A., 2004. South Carolina Water Plan, second edition. South Carolina Department of Natural Resources, Columbia, SC, 120 p. Buchleiter, G.W., Camp, C.R., Evans, R.G., King, B.A., 2000. Technologies for variable water application with sprinklers. In: Evans, R.G., Benham, B.L., Trooien, T.P. (Eds.), Proceedings of the 4th Decennial National Irrigation Symposium. American Society of Agricultural Engineers, St. Joseph, MI. Camp, C.R., Sadler, E.J., Evans, D.E., Usrey, L.J., Omary, M., 1998. Modified center pivot system for precision management of water and nutrients. Appl. Eng. Agric. 14 (1), 23–31.
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