Robert W. Coates

Control of individual microsprinklers and fault detection strategies

Based on yield variability in orchards, it is evident that many trees receive too much or too little water and fertilizer under uniform management. Optimizing water and nutrient management based on the demand of individual trees could result in improved yield and environmental quality. A microsprinkler sensor and control system was developed to provide spatially variable delivery of water and fertilizer, and a prototype was installed in a nectarine orchard. Fifty individually addressable microsprinkler nodes, one located at every tree, each contained control circuitry and a valve. A drip line controller stored the irrigation schedule and issued commands to each node. Pressure sensors connected to some of the nodes provided lateral line pressure feedback. The system was programmed to irrigate individual trees for specific durations or to apply a specific volume of water at each tree. Time scheduled irrigation demonstrated the ability to provide microsprinkler control at individual trees, but also showed variation in discharge because of pressure differences between laterals. Volume scheduled irrigation used water pressure feedback to control the volume applied by individual microsprinklers more precisely, and the average error in application volume was 3.7%. Fault detection was used to check for damaged drip lines and clogged or damaged emitters. A pressure monitoring routine automatically logged errors and turned off the microsprinklers when drip line breaks and perforations caused pressure loss. Emitter diagnosis routines correctly identified clogged and damaged microsprinkler emitters in 359 of 366 observations. Irrigation control at the individual tree level has many useful features and should be explored further to characterize fully the benefits or disadvantages for orchard management.

Wireless mesh network for irrigation control and sensing.

Variations in plant water and nutrient demand and environmental regulations to protect water quality provide significant justification for site-specific irrigation and fertigation systems. We have developed wireless valve controllers that self-assemble into a mesh network. Mesh networking means that controllers pass messages to extend the effective communication range without using high-power radios. Solar energy is collected with a 200 mW panel to operate each controller node without yearly battery replacement. Nine nodes were tested in a mesh network, and each properly responded to commands. Measurements of battery voltage, solar panel voltage, enclosure temperature, and external sensors were transmitted every 10 min. Irrigation schedules were stored locally on each node and executed automatically. Schedules for each node were unique, based on the needs of the particular area being irrigated. Internal clock drift was an average 6.3 s per day. Clock offset was removed using daily time stamps. One-hop transmission range using 916 MHz radios varied from 20.9 m with a whip antenna at ground level to 241.1 m with a dipole antenna at 3 m. Node commands were acknowledged after an average of 2.7 s per hop. Charge consumption was approximately 7.03 mA·h per day for the node circuit and 1 mA·h per day for battery self-discharge. The solar panel produced 26.0 to 81.3 mA·h in direct sunlight and 6.5 to 13.7 mA·h in shade. Node operation is expected to be continuous with occasional sunlight exposure. Soil moisture, pressure, temperature, and other environmental sensors will be used for feedback control and detection of problems. Such a network of intelligent valve controllers will allow growers in orchards, vineyards, nurseries, greenhouses, and landscapes to develop management practices that improve water- and fertilizer-use efficiency.

Design of a System for Individual Microsprinkler Control

A new microsprinkler system was developed to allow spatially variable delivery of water and fertilizer. A prototype was installed along 50 trees in a nectarine orchard. Individually addressable microsprinkler nodes were located at each tree, and a drip line controller that stored the irrigation schedule and issued commands to each node was installed at one corner of the orchard. Each microsprinkler node included a standard microsprinkler emitter, latching solenoid valve, and control circuit. A master computer allowed remote access to the drip line controller using a wireless modem. Tests were conducted to evaluate power consumption, valve and communication reliability, wireless range, and individual microsprinkler control. A lead-acid battery with solar charger powered the system for ten continuous days with no decline in average daily voltage. While testing prototype reliability, four communication errors and three valve errors occurred out of 10,250 operations. Wireless communication range between the master computer and drip line controller was 600 m with line-of-sight and 130 m with obstructions. The ability to provide microsprinkler control at the individual tree level was demonstrated by operating the emitters for different durations.

Site-specific water and chemical application by wireless valve controller network.

Variations in plant water and nutrient demand and environmental regulations to protect water quality provide significant justification for development of site-specific irrigation and fertigation systems. We have developed wireless valve controllers that self-assemble into a mesh network. Mesh networking means that controllers pass messages to extend the effective communication range without using high power radios. Solar energy is collected with a 200 mW panel to operate each controller node without yearly battery replacement. Nine nodes were tested in a mesh network and each properly responded to commands. Measurements of battery voltage, solar panel voltage, enclosure temperature, and external sensors were transmitted every 10 minutes. Irrigation schedules were stored locally on each node and executed automatically. Schedules for each node were unique, based on the needs of the particular area being irrigated. Internal clock drift was an average 6.3 s per day. Clock offset was removed using daily time stamps. One-hop transmission range using 916 MHz radios varied from 20.9 m with a whip antenna at ground level to 241.1 m with a dipole antenna mounted at 3 m. Node commands were acknowledged after an average of 2.7 s per hop. Daily charge consumption was approximately 6.76 mA·h for the node and 1 mA·h per day for battery self-discharge. The solar panel produced 26.0 to 81.3 mA·h in direct sunlight and 6.5 to 13.7 mA·h in shade. Node operation is expected to be continuous with occasional sunlight exposure. Soil moisture, pressure, temperature, and other environmental sensors will be used for feedback control and detection of problems. Such a network of intelligent valve controllers will allow growers in orchards, vineyards, nurseries, greenhouses, and landscapes to develop management practices that improve water and fertilizer use efficiency.

Precision Irrigation and Fertilization in Orchards

The development of a spatially variable microsprinkler system was shown. The system consisted of individually addressable microsprinkler nodes and a drip line controller which issued commands to each node. A demonstration system was constructed and preliminary field tests were conducted. Results show that individual microsprinkler control is possible and development will continue.

Fertigation techniques for use with multiple hydrozones in simultaneous operation

Site-specific delivery of fertilizer is a useful tool to address differences in crop need. Modern systems with wirelessly networked sensors and valves allow multiple hydrozones to be created more easily than traditional wired systems. This allows irrigation and fertigation rates to be varied across small portions of a field. However, fertigation to multiple hydrozones with different fertilizer requirements may be complex if each zone cannot be fertigated in an independent set. Instead, it might be necessary to operate several fertigation zones simultaneously. This raises a concern over the ability to deliver fertilizer uniformly within each zone. Four fertigation strategies were tested. The conventional method was to fertigate multiple hydrozones at different times. Three site-specific strategies were considered, involving overlapping fertigation phases in multiple hydrozones. Fertilizer distribution uniformity tests were conducted with a 64-emitter drip line to determine which strategy gave the most uniform distribution of fertilizer within a hydrozone. All fertigation techniques performed well, with fertilizer distribution uniformities between 0.88 and 0.96. Selection of the optimum site-specific fertigation strategy will depend on crop needs, scheduling limitations, and system design parameters such as emitter type, fluid travel time, and slope. Similar to conventional fertigation, the main factor in fertilizer distribution uniformity for this study was drip emitter variability. In the presence of sloped terrain, the site-specific control strategy that involved a delay between fertilizer injection and flushing had the least uniform fertilizer application.

Wireless Sensor Network for Precision Irrigation Control in Horticultural Crops

Wireless sensor networks for crop monitoring have become more common, but typically support sensing only and not control. Much of the work on wireless sensor networks with integrated control has been conducted in academic research. To promote the accessibility of commercially-available wireless sensing and control networks, valve control hardware and software were developed to be compatible with a commercial wireless sensor node. The work was conducted in collaboration with a wireless network vendor such that the research conducted with this wireless system and the product itself would be available to growers. The valve actuation system included custom node firmware, actuator hardware and firmware, and base computer communication software and a web interface. Network range, energy consumption, and actuator operation were characterized. A commercial soil moisture sensor was selected to monitor nursery container water content for closed-loop irrigation control in container nurseries.

Solar-Powered, Wirelessly-Networked Valves for Site-Specific Irrigation

Site specific irrigation and fertilization have been proven as useful tools for crop management. Existing technology generally limits the scale at which site management can take place since fields are divided into management units which contain multiple sprinklers or emitters. Control of each individual or smaller groups of emitters in an irrigation system may improve water and fertilizer use efficiencies, and reduce runoff and leaching. Controllable valves would operate from a schedule based on plant or field conditions. This would be useful in orchards and landscaping to irrigate trees or plants with different water or injected fertilizer requirements. In a container nursery, the individual schedules could be changed to accommodate inventory movement. We are developing an irrigation system consisting of a network of irrigation valve controllers. Each valve controller will operate autonomously from a locally stored schedule and communicate with a field controller using wireless communication. Mesh networking will be used to increase the range of the network. The line-of-sight range of a single unit was about 30 m. Each valve controller will be powered by a battery coupled to a solar panel for recharging. This will allow several years of operation before battery replacement is required. Solar panel energy production in sunny and shaded conditions will be adequate if radio communication time is carefully managed. Latching valves were selected due to their low power requirements. We will develop strategies for accurate control of water discharge, fertilizer application, and detection of fault conditions, such as clogging or breakage.

Site-Specific Water and Nutrient Application by Wireless Valve Controller Network

Variations in plant water and nutrient demand and environmental regulations to protect water quality provide significant justification for development of site-specific irrigation/fertigation systems. But to be accepted by growers, a system must be easy to install and operate. We have developed wireless valve controllers that self-assemble into a mesh network. Mesh networking means that controllers pass messages to extend the effective communication range without using high power radios. We are currently designing a system using low-power wireless modules designed specifically for sensor networks. Solar energy is collected with a miniature panel to operate each controller node without yearly battery replacement. In lab testing, nodes properly responded to commands to open or close a latching valve. Transmission range using 900 MHz radios with dipole antennas varied from 32 m to 217 m depending on obstructions and antenna height above ground. Node current consumption during idle periods was about 180 µA. Current consumption during radio transmission and receiving was about 15 mA. The solar panel produced 52 to 81 mA-h in full sun and 6 to 10 mA-h in shade. Soil moisture, pressure, temperature, and other environmental sensors will be used for feedback control and detection of problems. Such a network of intelligent valve controllers will allow growers in orchards, vineyards, nurseries, greenhouses, and landscapes to develop management practices that improve water and fertilizer use efficiency.