Combine timely irrigation with good crop management and 250 bushels per acre is a reachable yield for many corn farmers, according to Georgia Extension Agronomist Dewey Lee.
He cites long-term records showing dryland corn  produces only 48 percent of the yields coming from irrigated corn.
Cultural practices such as hybrid selection, plant population, fertilization and crop protection all change under irrigation, according to Lee. When growing corn, he says producers should assume yield-reducing droughts will be the norm rather than the exception.
Corn crops need water starting immediately after planting and continuing through the black layer stage when the plant reaches physiological maturity. Water use by corn peaks during a period from the time of tassel emergence through the dent stage.
Well-timed irrigation can eliminate moisture stress during critical plant growth periods, and help the crop efficiently use fertilizer and other inputs. Irrigation scheduling can be simple or complicated, and Rad Yager has some tips for farmers to use in timing their irrigation applications.
Yager works as an Extension agent in Dougherty County, Ga., and as a water Extension and outreach specialist at the Stripling Irrigation Park near Camilla, Ga. He recently reported on an irrigation scheduling project he worked on that was sponsored by the Georgia Corn Commission. “I also had a great deal of help from the Stripling Irrigation Park and the Flint River Soil and Water Conservation District,” he noted.
“Our growers are already good irrigators,” says Yager. “They know their crops, their fields and which ones are drought prone.” Like most farmers, he knows that irrigating too late will cause yield losses while irrigating too much will waste energy, money, water and can leach nutrients.
Several methods are available for scheduling corn irrigation. The simplest is probably the checkbook method. It requires a rain gauge along with knowledge of soil type, daily corn water use and the water holding capacity of the soil. The EASY pan method was developed by the University of Georgia and focuses on moisture loss from pan evaporation. Another is Irrigator Pro, an expert system developed by USDA researchers at Dawson, Ga. Also, soil moisture measuring devices such as the Echo and Watermark models can be used with corn growth curves to aid in irrigation scheduling.
Though some farmers use soil moisture sensors, crop irrigation models and take pan evaporation readings, Yager says most farmers irrigate by intuition. He believes farmers could improve their irrigation results by using one of the more sophisticated methods of irrigation scheduling. Irrigation scheduling methods are inexpensive compared to the investment in irrigation equipment .
The project Yager worked on was designed to bring some of this irrigation scheduling technology to south Georgia farmers. The focus was on using soil moisture sensors to pin-point the soil moisture conditions that call for irrigation prior to the crop entering a period of drought stress. Another goal was to make this information easily accessible.
“We used some sophisticated measuring devices,” says Yager. “An expensive one came with five sensors on the probe, and it was very accurate. We also used radios and cellular phones to transmit the data to a Web site every 15 minutes. Doing this allowed us and the farmers to check the soil conditions remotely.”
He described the data provided by one of these soil moisture monitoring systems on a farm field in Berrien County, Ga. “We used the data to generate a graph showing the number of days the crop was stressed in 2009,” he says. “The soil moisture data came from sensors placed four, eight and 12 inches deep in the soil. The graph also showed the influence of plant water use during the day and during the night.”
The graph from last June showed there were about three to four days between irrigations. “Irrigation was started on June 12 to keep the soil moisture level close to field capacity,” he said. “After two irrigations, the field received rainfall on June 18, and the farmer turned off the irrigation. The local Extension agent checked the data on the Internet and saw the rain did not recharge the moisture.” In this case, the farmer would have been better off to continue irrigating, even during and after the rain. Yager said the data also showed the farmer might have wasted some water when he resumed irrigating on June 21. “He applied the irrigation to catch up on the lost soil moisture and when he did his irrigation exceeded the field capacity.”
Yager later received an e-mail message from the Berrien County farmer who said he was impressed with the results of the soil moisture monitoring, and that he would use the technology again in 2010.
On another farm in Mitchell County, Ga., the sensors showed the effects of a good rain on June 4. By June 10, this moisture was depleted and the crop needed to be irrigated. “But the irrigation pump went down,” said Yager, “and we saw the soil moisture level decreasing steadily after that.” After the irrigation pump was repaired, the farmer put out three light irrigation applications during a period from June 16-19 to help catch up. Then, on June 29, another good rain fell and this helped get the crop through its critical period for moisture requirements.
The soil moisture sensors are not without their problems. Yager said some of these challenges include initial expense, the time it takes to install them and the time it takes to evaluate the data. Durability of the devices can also be an issue. “If the installation is not done properly, you can get bad data,” says Yager. “We had to re-install one of the sensors on a farm last year in Terrell County, Ga.”
Overall, Yager says the sensors and the crop models will make farmers better irrigators. “But you need to balance out the potential benefits with the potential problems,” he says. “It definitely takes some experience to be able to accurately read and interpret the data.”
Yager intends to continue with the project in 2010. He also notes that the Flint River Soil and Water Conservation District through its Advanced Irrigation Management (AIM) program is providing attractive cost sharing in an effort to get more of these soil moisture sensors out on farms.
For more information, growers might want to refer to a publication entitled A Guide to Corn Production in Georgia 2010, which is published by the Georgia Cooperative Extension Service.