Irrigation of crops in the Mid-South has grown by leaps and bounds over the last two decades, but an ongoing challenge for farmers has been to improve the accuracy and timeliness of water applications.

A research project under way in Mississippi may hold a solution.

With the online scheduling tool being developed, a producer could log onto a Web site, plug in information such as field boundaries from aerial photos, crop planting date, soil moisture present in the field, etc. The program would then update the weather information to add current and predictive weather data and suggest the best time to apply irrigation (or if rain is predicted, the producer could elect to hold off on the application).

After an irrigation application, or if rainfall occurred, that information would be added in order to determine timing of the next irrigation.

The tool will work for all types of irrigation delivery systems — sprinkler, flood, and furrow — and flow rates.

“For nearly two years, we’ve been working to develop the online irrigation scheduling tool,” says Amy Schmidt, assistant Extension professor in the Department of Agricultural and Biological Engineering at Mississippi State University.

She is part of a team that includes Gretchen F. Sassenrath, plant physiologist, and Daniel K. Fisher, agricultural engineer, both with the USDA-Agricultural Research Service Crop Production Systems Research Unit at Stoneville, Miss.; Lyle Pringle, associate agricultural engineer at the Delta Research and Extension Center, Stoneville; and Scott Samson, Extension professor in the Geosystems Resources Institute at Mississippi State University, who is managing the computer coding and web site development.

“Our goal is a reliable, easy to use irrigation scheduling tool that integrates crop monitoring, current weather, and weather predictions to improve the timing and application of irrigation in the humid, high rainfall environment of Mississippi,” Schmidt says. By making the scheduling tool Web-based, producers will be able to access the tool from mobile devices, including phones.

Saving energy through reduced pumping

“While we hope there will also be water conservation benefits, the main goal is to provide producers with a tool that will allow them to better time irrigation applications and to save energy by not pumping water when they don’t have to.”

Funding assistance from the Mississippi Soybean Promotion Board will continue the project through March 2011 to allow beta testing of the program with producers.

“Dr. Sassenrath has identified soybean producers in the Delta who she and I will work with to test the tool and determine how easy it is for them to enter field data, how effective the tool is, and what may be missing that would make it work better,” Schmidt says.

While the tool is initially being used with soybeans, it will also be adapted to cotton and corn, with a possibility of later including rice.

There are a couple of tools of this type being used in Midwest states, she notes, but nothing for the humid South. “If it proves effective for Mississippi producers, we could then potentially expand it for use by growers in other southern states.

 “By next summer, we should have enough experience and input from the initial group of producers to decide whether to continue the project,” Schmidt says. “If it goes forward, we would hope to make it generally available for the 2012 crop season.”

Even though Mississippi receives high rainfall — in excess of 40 inches annually — over the past several years more water has been pumped from the alluvial aquifer than is being replenished, which has begun to deplete the aquifer.

If soil moisture isn’t sufficient during the growing season, crop yields and profits suffer. Weather-related risks have increased the use of irrigation in the Delta, which has resulted in an average decline in the alluvial aquifer of 300,000 acre feet per year over the past 10 years.

No readily available, accurate, easy to use irrigation scheduling tools have been developed and calibrated for the environmental conditions and crops in the area.

'Checkbook' method to determine when to irrigate

“Wise water management requires knowledge of how much water the crop needs and when that water is needed,” Schmidt says. “More effective irrigation scheduling can help producers to better match the timing and application of irrigation with crop water use.”

In a paper to be presented later this year at the American Society of Agricultural and Biological Engineers’ national irrigation conference, the researchers note that irrigation in hot, humid areas is “particularly challenging,” because water must be applied in a timely manner to prevent yield loss due to crop water stress, while avoiding flooding should rain occur following an irrigation.

Also, it is difficult to detect the onset of crop water stress under environmental conditions that limit evaporative cooling.

The irrigation decision support system is based on calculations of crop water use from weather data collected from weather stations throughout Mississippi, using crop coefficients developed from weighing lysimeters.

A “checkbook” method is used to indicate when supplemental irrigation is needed, based on water available to the plants and crop water use. The method is very similar to a check book, with inputs to the available soil water from rainfall and irrigation being “credits”, and use of soil water by crops being “debits”. As the daily soil water balance decreases with crop growth, the loss of soil water to a predetermined negative balance indicates the need to irrigate.

The tool will be integrated with other publicly available, spatially registered farm and soil databases to reduce the amount of data the farmer needs to enter, and develop the irrigation scheduling recommendations. It calculates crop water use and suggests a need to irrigate based on the irrigation system and the allowable deficit set by the producer. Key data needs and calculations include weather data, crop coefficients, estimated soil runoff, and soil information.

The irrigation decision support system will be delivered to producers through an easy to use and readily accessible format. Training materials will be developed and presented to producers through on-site training and other Extension systems.

Decisions based on what neighbors do

The most commonly used method of irrigation scheduling has been based on the feel of the soil, the researchers note, which provides no quantitative measure of crop or soil water status. Studies have shown that more than 25 percent of producers base their decision on when to start irrigating on what their neighbors do.

Sensors can also be placed in the rooting zone to measure soil moisture during the growing season. As the plants grow and remove moisture from the soil, depletion below a certain level indicates that irrigation is needed.

While sensors are accurate if properly installed and maintained, they can be expensive, difficult to install and time-consuming to read and record data regularly, and so the researchers did not want to rely on them.

Wise water management requires knowledge of how much water the crop needs and when the water is needed. Irrigation scheduling is a method of managing water to better match the timing and application of irrigation with crop water use.

In high-rainfall areas, like Mississippi, the uncertainty of amount and timing of rainfall makes irrigation scheduling particularly challenging, since a high rainfall event immediately following irrigation can result in waterlogged soils that impede crop growth.

The challenge for Mississippi producers is to manage water resources appropriately and provide sufficient water for crop production during the droughty periods that occur during the growing season, the researchers note.

“Particularly critical to the continued success of agriculture in the Mississippi Delta is the development of accurate and easy to use guidelines for irrigation scheduling and application.

“From previous research, we know that farmer acceptance of new technology is often predicated on their accessibility to scientists and Extension personnel. A significant component of our research is to develop educational tools to enhance understanding and adoption of the new technologies.

“The most important indication that a tool is considered worthy by producers is that it gets used.”

To that end, they have focused on several key points in developing the irrigation tool:

—It must be easy to use, understand, install, and update.

—Data requirements should be minimal.

—Data collection should be as “invisible” as possible through automatic downloading of information such as weather data.

—It should seamlessly integrate with other programs, such as recordkeeping, conservation, etc.

—It should be acceptably accurate, given the data input.

Field and irrigation system data must be entered by the producer. Scheduling is arranged by water source to allow the coordination of fields serviced by particular wells.

The irrigation scheduling Web site would be operated by the Mississippi Extension Service and maintained at Mississippi State University.