Session 7. Sensors and Controls in Microirrigation
A Modified Tensiomether for Control of Potted Plant Irrigation in Nurseries
F. S. Zazueta, M. Valiente-Gomez, J. I. Valiente-Banuet, T. Yeager
A soil water status measuring device and its use in a greenhouse is presented. The devise is based on tensiometric measurements. It consists of a porous plate placed at the bottom of a cylinder with a pressure transducer to measure matric potential. The device avoids problems typical of the use of conventional tensiometers in soil-less ornamental crop production. This device was used successfully with a closed-loop control system to control irrigation. The system consisted of a personal computer, a powerline modulated actuator, and a datalogger as the data acquisition interface.
Keywords: Sensors, control, automation, greenhouse
Abstract taken from paper found on pages 209 to 213 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG
Soil Water Sensor Placement and Interpretation for Drip Irrigation Management in Heterogeneous Soils
Many drip irrigation management schemes rely on frequent monitoring of soil water content and matric potential using various sensors (e.g., tensiometers, gypsum blocks, or time domain relectometry probes). The information is used either for scheduling irrigation, or for adjusting schedules based on evapotranspiration measurements. Most soils exhibit spatial variations in their hydraulic properties, which in turn, induce spatial variations in wetting patterns about the drippers. These variations present a problem for sensor placement relative to the dripper, and complicate interpretation of soil water information. The objective of this study was to quantify effects of mild spatial variation in soil hydraulic properties on the mean and variance of soil water content and matric potential distribution about point sources and the consequences on soil water sensor placement and interpretation.
The stochastic approach considers the soil properties as random space functions. A first-order small-perturbation expansion was applied to analytical solutions of stead state flow from point sources. The stochastic analysis presented here is limited to conditions of mild variations in soil hydraulic properties, for the following reasons: (i) most agricultural fields are selected on the basis of homogeneity in soil conditions (within plant rooting zones); and (ii) such conditions are amenable to first order statistical analysis which yields analytical solutions. The resulting analytical expressions relate the variability of soil hydraulic properties to the expected variability in matric potential and relative saturation. Comparisons of analytical predictions with Monte Carlo simulations for surface and buried sources resulted in excellent agreement. The expressions may be used to define regions with smaller uncertainty for better monitoring, or for determining the minimum number of sensors needed to obtain estimates with a prescribed estimation error.
Keywords: Steady state flow; Drip irrigation; Stochastic analysis
Abstract taken from paper found on pages 214 to 222 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG
Solar Power Supply System Design for Irrigation Control at Remote Sites
R. J. Edling and M. J. Gaspard
An irrigation control system for remote sites powered by solar energy is being developed. The system consists of the solar array. solenoid valves, voltage regulator, inverter and storage battery. Methods of determining the size of the solar array, estimating the daily energy output from the array, determining the size and type of battery needed and other information about the circuitry are discussed. Field tests in 1994 indicated that the energy demand to operate the system exceeded that produced from the array. The inverter, in particular, now places excessive demands on the system. Plans are being made to reduce the energy demands of the inverter by incorporating a solar cell switch. The inverter will be off at night and during the middle of the day.
Keywords: Photovoltaic cells, solar power, solar energy, microirrigation, controller
Abstract taken from paper found on pages 223 to 227 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG
Irrigation Automation Conserves Resources to Meet Demands of a Changing World
Doug W. Champion and Susan Suggs
The Wilbur® irrigation and mist control system combines easy to use software, reliable hardware and proven surge protection against lightning and provides features growers want. It results from ten years of development and feedback from users of the system. Automation features include sensor based control, warnings and phone/pager communication. Based on sensor input, the system can start, stop, delay, or skip a task and deliver phone messages.
The system provides off site control of irrigation and mist via phone lines. The system can call a preset number at a set time with a message that irrigation is proceeding as scheduled.
With the Wilbur resource manager, the grower can easily implement a pulse irrigation program saving at least 20% in water and also reducing runoff, power consumption and chemicals used. The system detects abnormal flows and issues warnings.
With flow meters, the system keeps precise records of when, where and how much water was applied allowing growers/researchers to experiment with various watering regimens, determine water savings and implement the optimum schedule for each crop.
The system significantly reduces human labor. It is automatic. Human inputs are required only as crop water needs change. Rescheduling is quick. The warning and communications abilities free up manpower for other tasks including those off site. Remote control and monitoring is possible.
The Wilbur system's unique mist control varies the amount of mist by the hour. Coupled with sensor based control, growers increase propagation percentages.
Growers will use automotive resource management to remain competitive, reduce labor and meet environmental requirements. Remote control ad monitoring of irrigation will increase. Growers will track their water usage. Additional applications of sensor based control will be developed as sensor technology improves. Intricate watering regimens will be implemented which save water and improve plant vigor.
Keywords: Irrigation control, sensor based control, automation, mist control, pulse irrigation
Abstract taken from paper found on pages 228 to 233 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG
Advances in Microirrigation Control by Sap-Flow Monitoring Systems
M. G. van Bavel
Over the last seven years, new advances in the techniques for sap-flow measurement have made the measurement of water use in crops, trees and vines a simpler and more economical process. A new system design is explained and a new microirrigation controller implementation is proposed in this paper. The method has been studied, and research has proven the utility of the heat balance sensor method of determining transpiration (T) and how it relates to sap flow(F). Many crops have been measured in the field under realistic conditions, and studies are proving the utility of the method in a variety of applications of stem gauge, a sensor produced with the heat balance theory. Citrus and fruit growing applications have recently been explored and are shown to be useful in determining water stress and in relating water consumed to the amount of hourly or daily evapotranspiration (ET) demand. Two new sap flow monitoring systems have been recently produced which are being adapted for the closed loop, automatic control of water valve timing needed to keep crop production at a peak, while minimizing water use and preventing water stress. Although many more species need to be tested using stem-flow technology, many of the principal economic crops of the world have been shown to be effectively monitored using stem gauges.
Keywords: Sap flow measurement, heat balance, in situ, microirrigation, microcomputer control, water stress
Abstract taken from paper found on pages 234 to 238 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG