Preview: Irrigation Management Tech section from the future Almond Production Manual

Hello Patreon members! I know the website has been inactive over the past few months. Some of this is due to a larger effort by me to help complete "The Almond Production Manual," a remaining task from my time with UCCE. One part of that was the construction of a section within the Irrigation chapter, titled "Irrigation Management Technology." I have included it below for your review, thoughts, and use.Irrigation Management Technology – David DollDue to the complicated nature of irrigation scheduling, there has been efforts to develop simplified tools for use by farm operations. Traditional recommendations in irrigation management have relied on three principles to help refine irrigation scheduling. These include crop ETc estimation, soil moisture monitoring, and plant stress monitoring. In the past, these three areas were typically managed by calculation of an ETc estimate, soil moisture sensors, and the pressure chamber. Although these tools still exist and are very effective, in recent years, the number of companies offering irrigation solutions has increased dramatically. These tools tend to utilize various technologies to determine how much water to apply, in-field monitoring of the soil and plant status, and finally, services to help with water resource management and application. Although it is difficult to determine what tool is best as this is dependent on the site and farm operation, an overview of the technologies will be provided.Irrigation scheduling and ETc estimation. As described in this chapter, irrigation scheduling takes time. Many tools and strategies have been developed to assist with ETc estimation and calculation. Many of these are as simple as programs that calculate ETc and help determine run times. Others are as complicated as determining daily water use and helping to refine site specific Kc values for a field.Probably the most widely installed tool to assist with ETc estimation is on-farm weather monitoring equipment. Traditionally, farms use to utilize evaporation pans to estimate water use by the surrounding crops. This has been replaced by the evolution of affordable, very sensitive weather monitoring equipment that is connected to the farm’s information network. This equipment can measure the variables required to estimate ETo utilizing the Penman-Monteith equation. Variables required include temperature, wind speed, humidity, and solar radiation. Any weather station installed should provide these input variables or it will not be able to accurately estimate ETo, . Software packages included with the purchase of most weather stations used for agriculture typically calculate ETo values for use.Recently, there have been the development of in-field monitoring of water usage. Most of these efforts rely on either in-situ sensors being installed or use of satellite data. These technologies utilize localize temperature fluctuations and solar radiation to determine the amount of water vapor being emitted from an orchard. This method is known as surface renewal (Snyder, et al, 1996, Shapland, et al, 2014), and allows a site-specific water use estimation to be determined for an orchard. Although this technology has been considered more expensive in the past, recent advancements have lowered the costs, making it possible to integrate into orchard systems.Soil Moisture Monitoring Tools. Soil moisture sensors are great tools to aid in irrigation management. They provide feedback on the movement, depth, and quantity of moisture within the soil. This information can assist in determining the need to irrigate, as well as the proper duration of irrigation. Proper use relies on a thorough understanding of the soil characteristics of the orchard, which include soil type, water holding capacity, and salinity level.Traditionally, growers have relied heavily on the “feel method.” This method involves sampling the soil at varying depths and either making a ball or ribbon with the soil to estimate the level of available moisture. Although difficult to calibrate at first, after some practice this method is quite useful as it is quick, reliable, mobile, and free. This method is also useful in identifying variability and helping with the calibration other types of irrigation system management tools. Useful guidelines to help with the feel method have been developed by the USDA-NRCS and can be found online or at the local office.There are various sensor technologies that are currently on the marketplace to assist with soil moisture monitoring. Most of these are based on four technologies, which measure one of the following: soil tension, di-electrical constant, electrical resistance, or movement of neutrons. Each of these methods have differing benefits and drawbacks, which can be seen in table 1. Work by the University of California has compared many soil moisture monitoring systems. Neutron probe data, dielectric, tensiometers, and electrical resistance blocks have all been found to respond to water applications similarly. Essentially, if sensors are properly installed and maintained, and time is taken to understand and interpret the data, they can provide similar information.Sensors can be used to help schedule irrigation. Timing of irrigation usually occurs when moisture levels drop below certain trigger points at varying depths. These points are different for every soil and sensor type and require in-field calibration to help reduce unwanted plant stress. Calibration can occur by comparing sensors readings to plant stress responses (e.g. Pressure chamber readings) or to a “feel” test to determine how much water is still available to the plant.Several factors need to be considered when planning to install the sensors. Sensor locations should be placed to account for varying soil types of the orchard. If only a few locations are planned, the predominant soil types should be selected. If possible, sensors should be installed at varying depths to provide moisture levels in the middle, bottom edge, and below the active rootzone. A common 3 sensor installation pattern is 12-18″, 30-42″, and 48-60.” Lastly, dependent on the sensor technology, the area of moisture detection can be extremely limited. Soils with high amounts of variability may require a greater number of sensors or technologies that have measurements over a larger soil volume.Remote sensing methods of soil moisture measurements. With ongoing improvements in sensor technology, sensors that were once thought to be unaffordable have dropped significantly in price. Two technologies that may see an increase usage in helping to manage soil moisture and site variability are LIDAR and satellite imagery. LIDAR, which stands for light detection and ranging, uses light pulses which the sensor uses to help construct three-dimensional information about an area. Since water has an impact on how the light is reflected to the sensor, this tool can be used to estimate soil moisture levels over large areas. Although this technology has not been thoroughly refined for use within permanent crop agriculture, it has increasing interest due to its ability to measure soil moisture levels over large areas accurately and quickly, assisting with identification and management of variable soils.Satellite imagery can also be used to estimate soil moisture levels. Satellites can provide accurate soil moisture estimates by measuring the microwaves that are reflected by the Earth’s surface. This technology is proven and has been collected for over 40 years by various government organizations and utilized for weather and climate forecasts. Until recently, however, the resolution of the measured surface was not refined enough for site-specific uses. Recent satellite launches, both from government and privately funded projects, will improve resolution to within 3 meters (10’), which would provide a useful tool to utilize in collaboration with in-the-field soil sensors.Plant based Measurements. Plant stress monitoring has been considered one of the more important input variables into irrigation scheduling. Having the ability to monitor if a tree is over- or under-irrigated can help reduce water while increasing almond yields. Traditionally, this has relied on the use of stem water potential measurements (SWP) which utilize the pressure chamber. The use of the pressure chamber is described more thoroughly in the chapter “Physiological aspects of water use.” This measurement has been thoroughly researched and the results have been verified in multiple research trials across several crops over the past 40 years. All other plant-based monitoring technologies have utilized this system to correlate measurements to tree stress.Additional in-situ plant-based measurement technologies include dendrometers and “sap-flow” sensors. Dendrometers measure the shrink and swell of a tree which occur naturally through the day. As the tree requires water during the day, the plant tissue shrinks due to water loss. At night, this tissue recovers – often to a greater level than experienced the day before. If the ratio of shrink/swell decreases, that means the plant is stressed and irrigation is required. Dendrometers have shown a close correlation with SWP. In the past, this technology was considered too tedious to install and manage within an orchard. Due to the lower costs of the precision equipment and the ability to utilize cellular/wireless data, this technology has been successfully launched into a service for almond orchards.In-situ “sap-flow” sensors aren’t as developed as dendrometers. These sensors are embedded into the tree and measure several variables of flowing xylem components to estimate an energy balance. The implementation of these types of sensors have been successful in other crops, but challenges still occur within almonds due to the secondary woody tissue growth. As sensitivity improves, however, these sensors may have the ability to correlate with SWP. Due to the novelty of this technology, a grower should ask to see any supporting research-based information within almonds prior to installation.Aerial imagery has been identified as an effective tool for plant stress monitoring. This technology has utilized satellite imagery, low elevation aerial imagery, and more recently images collected by unmanned aerial vehicles (UAVs). Aerial imagery has been utilized in other crops, which have found that various vegetative indices, such as NDVI, can be correlated to water stress. Within almond, however, NDVI and other vegetation indices have not been as reliable in predicting water stress. This is due to the delayed effect that water stress has on plant growth. In essence, by the time the images can determine a difference in canopy, the effects of water stress have already limited canopy development. Thermal imagery, as well as modification of near-far red bandwidths, have been shown to correlate highly to SWP measurements. In the past, images from these bandwidths required expensive sensors, but prices have reduced over the past decade to allow for installation on planes and UAVs for usage. Correspondingly, there are now multiple companies providing aerial imagery, in which they typically include multiple indices in the analysis, including NDVI, thermal, and various internally developed “tree health” indices.Aerial imagery has the distinct benefit from other plant-based measurements due to its ability to detect plant stress and irrigation related issues over large areas. Currently, these flights are not feasible to conduct continuously, as it is expensive to fly aircraft and operate UAVs, as well as is takes time for image processing. As such, it is best to view these technologies as “check-ups” on the field, in which performing an analysis on occasion through the year can help identify irrigation issues which can be directed for repair. In the future, satellite resolution may improve to levels feasible enough for irrigation scheduling (less than 1-meter pixels), which could be useful for both irrigation scheduling and identifying issues.Additional tools to help with irrigation scheduling and monitoring. The increased affordability of cellular data, wireless networking, and internet connection on the farm has increased the possibilities of what data can be collected on the farm. Operations are utilizing automatic reporting water meters, automatic valves, irrigation controller systems that can be accessed and programmed remotely, and various equipment monitoring tools to determine the need for maintenance. Furthermore, multiple companies are integrating artificial intelligence into the software platforms to assist with routine decisions.Many companies are offering a variety of tools, techniques, and software programs to help manage soil variability. These products typical include automated valve control units, creating the ability to turn on or off valves based on a programmer. Unfortunately, many of them are being retrofitted to older irrigation system that have been designed and installed, reducing the effectiveness to apply site specific irrigation recommendations. To fully implement these technologies, irrigation systems will have to be designed to be managed differently. This includes smaller irrigation areas controlled by each valve, more valves within a field, and a clear understanding of soil variability integrated into the design.Regardless of the system utilized, the farmer needs to remember to double-check the analysis provided by the technology. These tools are here to help facilitate the timely application of water, but they are not replacements for “boots on the ground.” Even so, as these tools continue to develop and integrated into farms, an improvement in irrigation performance should occur, allowing farmers to maximize water use efficiency while reducing time commitment across their operations.Table 1: IrrigationTechTable