Agricultural Water Conservation
SIRP actively participates in researching and implementing the latest agricultural water conservation tools. The park provides onsite demonstrations, field days, and tours highlighting new technologies offered by several different companies. SIRP is an ideal facility for bringing new methods and ideas from the lab to the working farm. Agricultural water conservation is vital to the future of south Georgia’s economic, social, and environmental health. The Floridan aquifer provides the main water source for the region’s farmers and the interacts geologically with the flows of the Flint River. In times of drought, there is often conflict over water consumption and streamflow. With this area of Georgia receiving 52 inches of rain annually, why is there still a need for irrigation? The majority of rainfall does not occur with precise timing or amount during critical growth stages for the crops, so farmers supplement any natural rainfall with irrigation to ensure their crops’ health and yields. Agriculture is the chief economy of this region, producing over $2 billion in farm-based revenue and approximately $70 billion statewide. The Flint River (and its tributaries) is also home to an array of biological diversity, including federally endangered mussel species. During times of drought and intensive agricultural irrigation, the streamflow of the river and streams can be reduced to harmful levels for these species as well as many others dependent upon a healthy and generous flow of the water throughout the year. This environmental interest coupled with the economic significance of agriculture bring agricultural water conservation and efficiency to the forefront of southwest Georgia’s priorities. Persistent droughts, energy costs, urban expansion, and interstate litigation are collectively threatening irrigation water supplies in the Southeast. Conservation of agricultural water is critical for sustaining the economic development of rural farming areas. University of Georgia Extension estimates that 1 inch of water costs $12 per acre-inch through overhead sprinkler application. Growers are interested in precision irrigation applications that allow for less water use while maintaining optimum yield. Examples of some conservation practices implemented at SIRP and in the surrounding basin are listed below:
Variable Rate Irrigation
(VRI) is a tool of precision agriculture that optimizes irrigation water application. Most fields are not uniform due to natural variations in soil type or topography, but center pivot irrigation systems still apply a singular rate across the field without sensitivity to these variations. VRI technology enables farmers to more easily apply customized rates of irrigation water based on individual management zones within a field. Developed by researchers from the University of Georgia, including SIRP Superintendent Calvin Perry, VRI is now commercially available as a modular component on existing center pivots or as a component of new systems. Research shows that implementing a VRI system can result in water savings of up to 15%.
- Non-cropped areas
- Overlap with adjacent pivots
- Topographic variability
- Soil variability
- Hydrologic variability (boggy or dry areas)
- Multiple crops/crop stages
- Irregularly shaped fields
- Environmentally sensitive areas
Advantages of VRI
- Reduced input costs (pumping, chemigation)
- Enhanced yields and profitability
- More accurate water application
- Improved water use efficiency
- Water conservation
- Reduced weed and/or disease pressure
- Reduced runoff
The FirstWater Ag VRI system consists of multiple components. The Master Controller acts as the brain of the system. This controller is where irrigation rate maps are loaded, deleted, changed and/or executed. The Master Controller allows for up to five zones (each zone is made up of a pre-determined number or “bank” of sprinklers). To add more zones, an expansion node is necessary. Each expansion node allows for the addition of eight more zones for a maximum of forty-eight zones. Solenoid valves send pressurized water from the mainline to activate flow control valves on each sprinkler when needed. The solenoid valves along with flow control valves allow each bank of sprinklers to be shut off over non-cropped areas or allow for cycling (for less than full amount) when necessary. The 100% rate is the base rate of application set by the user on the manufacturer’s control panel. Cycling refers to turning a sprinkler bank on and off based on percent of a minute (for example, 40% refers to sprinklers on for 40% of a minute and off for 60% of a minute to achieve 40% of the base rate). The GPS receiver (insert photo VRIGPS.jpg) located on the end of the center pivot mainline allows for the rate map to be applied to the correct locations on the field. A pressure reducing valve (insert photo PressureReducingValve.jpg) is usually added between the water source and the pivot point to allow the pivot to enable sprinkler cycling (or shut off sprinklers) without excessive pressure buildup which could lead to damaged pipes.
How it Works
In the Super Duper PC software, the center pivot system dimensions, sprinkler banks/groupings, and sectors are defined. A bank of sprinklers can range from a single sprinkler to as many as 7-10 sprinklers. A sector represents the division of the pivot circle from 1-10 degrees of travel. A water application map is then configured in the software (by combining the banks and sectors with percent application) which establishes special management zones throughout the field. Management zones are the areas of the field requiring more, less, or no water application, such as non-cropped areas or boggy areas. The water application map can also be programmed to control the end gun and speed of the pivot system. The sprinkler banks that correspond to each designated management zone will apply the desired amount of water to each zone in the field, using GPS. Once the field management zones have been established, they are then digitally drawn in a grid system over a background image of the field. Once this map building process is complete, the file is uploaded to a USB drive and transferred to the Master Controller on the pivot. The Master Controller then manages the sprinkler banks so the pivot applies water at the desired rate across the field, maneuvering through each variation or zone with the specified amount of water being applied.
The development of VRI began around 1993 when The University of Idaho received a US Patent No. 5,246,164 for the “Method and Apparatus for Variable Application of Irrigation Water and Chemicals.” However, there is little evidence of actual development of a University of Idaho-based VRI system In 1999, The University of Georgia via the College of Agricultural & Environmental Sciences’ NESPAL group acquired a “prototype” VRI system developed by Greg Harting, who at the time was an irrigation manager for R.D. Offut Northwest (Boardman, OR). The following year UGA approached Ole Hansen with Computronics/Farmscan (Perth, Australia) to provide a more simplified electronic control system for VRI. The first Farmscan system was installed in February 2001 in Tifton at the UGA-Tifton campus. Computronics/Farmscan secured exclusive worldwide license from the University of Idaho in 2004. The same year, Hobbs & Holder LLC (Ashburn, GA) became the US dealer for Farmscan VRI. Using USDA-NRCS funding, the Flint River Basin Partnership installed twenty-two VRI systems in 2004-05. Another twelve systems were installed by UGA and Clemson under a NRCS CIG-funded grant project. Advanced Ag Systems (Dothan, AL) became the sole US dealer/distributor for Farmscan VRI in 2010. To increase distribution of its patented Farmscan VRI technology globally, Computronics/Farmscan signed an agreement with Valmont Industries Inc. (Valley Irrigation). Over the last few years, the major pivot manufacturers, Lindsay (2010), Valley (2010), Reinke (2013), and T-L (2013), have brought their own VRI products to the market. More recently, Trimble announced the acquisition of a New Zealand irrigation company that specializes in VRI (IQ Irrigation), adding another major player to the market. Since 2010, numerous grants and cost-share funding opportunities have led to the expansion of VRI installations. In October of 2013, Advanced Ag Systems announced… VRI is one of the main tools of agricultural water conservation, and as the technology continues to grow and improve, more farmers will adopt this irrigation tool.
Low Pressure Sprinkler Retrofits
Farmers began implementing center pivot irrigation systems in Georgia in the 1970’s, and the conventional models operated at high pressure with impact sprinklers spraying water from the top of the pivot mainline. However, converting these systems from high to low pressure with spray-type sprinklers on drop hoses generates considerable water and energy savings by applying water at a lower pressure more directly to the soil surface to reduce evaporation and wind drift losses. Combined with the installation of end gun controls to keep irrigation inside the field boundary and the repairing of leaks in the system, retrofitting a pivot can save up to 20% of water application.
Conservation tillage refers to using a cover crop and intentionally leaving plant residue from a prior crop in the field. This modifies plant rooting structure and physiology to enable more efficient water use by crops, and water holding capacity in the soil improves. Water infiltration rates increase. Soil temperature, evaporative loss, and field runoff decrease. Converting from conventional tillage to conservation tillage can reduce water use by up to 15%.
Advanced Irrigation Scheduling
Advanced Irrigation Scheduling identifies precise periods of time in which a farmer can irrigate by using objective field data such as soil moisture, soil temperature, crop growth stage and localized evapotranspiration (ET) data. Whereas VRI controls “where” the center pivot will irrigate, advanced irrigation scheduling answers the question of “when” to apply irrigation. Utilizing these tools has produced water savings by up to 15%.
Remote Soil Moisture Monitoring (RSMM)
The purpose of a soil moisture monitoring system is to deploy probes or sensors to detect soil moisture conditions which are critical to optimal crop production. Monitoring soil moisture status allows the farmer or consultant to detect plant stress before the plant displays obvious signs of stress. Avoiding this unneeded stress can provide more optimal growth, increase yields, and enhance the overall quality of the crop. RSMM may also help the grower avoid overwatering, thereby decreasing potential water logging of the roots, root diseases, unnecessary water use, and nutrient leaching from the root zone. Soil moisture monitoring probes and sensors are available from a number of vendors and come in many forms, shapes, and sizes. Some probes are directly installed into the soil near the crop root zone while others measure canopy temperature from above to indirectly quantify soil moisture status. Each probe or sensor differs in the sensing method for measuring the soil moisture. The soil water tension sensor uses the electrical conductivity between two electrodes embedded in a ceramic or gypsum material. The electrical resistance between the two electrodes increases as water is drawn from the material. This sensor is installed in the soil and responds to changing soil moisture conditions. The sensor can be read with a handheld meter or through various dataloggers and/or remote telemetry. Another sensor option is a capacitance probe. This probe consists of a number of sensors (made up of pairs of circular rings) mounted on a vertical column and is then protected by a waterproof outer tube. Capacitance soil moisture sensors use electronics to measure the dielectric constant of the surrounding material (usually the soil) which happens to be related to moisture content.. Soil moisture stress can also be measured indirectly using a canopy temperature sensor. One vendor determines temperature using an infrared thermometer. Research has shown that crop canopy temperature can be related to crop stress levels caused by lack of soil moisture. If the temperature of a crop reaches an above-optimal temperature for an elongated period of time, the individual plants transpire water less efficiently which can be detrimental to the overall yield. The majority of soil moisture sensing technology on the market allows the farmer to use the Internet to securely log in and access real-time data on which to base an irrigation decision. Sensors within the probes are often placed at multiple depths (8 , 16, and 24 inches, for example) below the soil surface so the farmer or consultant can better interpret crop water needs or plant stresses.
Water Balance Methods
Irrigation scheduling tools that predict when to irrigate based on weather and crop conditions are prevalent, and many of these are available in the form of computer programs or websites. Current weather data is used to calculate an amount of water that would be evaporated by a reference crop such as grass, and then a crop coefficient is used to scale that reference value to a specific crop need. The majority of these programs are based on the water balance method. Scheduling irrigation using a water balance, or checkbook method, is based on the available water in the soil profile. Like a checkbook, inputs are credited to the total soil water, and withdrawals are debited from the soil water. The inputs to the soil water are rainfall and irrigation. Withdrawals include transpiration through the plant, evaporation from the soil surface, and deep percolation into lower soil layers. During the growing season, evaporation and transpiration, commonly termed “evapotranspiration” and abbreviated “ET” are the most important processes by which water is removed from the soil. The key to using a checkbook method is knowledge of the available water capacity of soils. In the Southeast Coastal Plain, our soils are typically more sandy and can only hold about 0.08 inches of water per inch of soil. Some scheduling tools combine soil moisture monitoring with water balancing. This approach can prevent over-irrigating early in the crop season or under-watering later during peak crop water use.
The UGA EASY Pan (Evaporation based Accumulator for Sprinkler enhanced Yield) is an affordable and easily operable system that yields representative results in the humid region of the southeast U.S.. No record keeping is necessary for this method, and the unit can be read from a distance quickly. The float-based mechanism is designed to represent both the effective root depth of a crop and the soil water holding capacity. The screen covering the pan limits evaporation in a similar level to the evapotranspiration rate of a crop. The EASY pan can be constructed using affordable and readily available products. UGA Extension provides instructions on how to build an EASY pan and also how to calibrate it for certain crops and soil types.