Automating aeration of stored rice can reduce the use of pesticide fumigation in on-farm storage bins, said Terry Howell, food engineer for the Arkansas Agricultural Experiment Station.
“On-farm rice storage is expanding to more farms each year,” Howell said. “During storage, the rice is aerated to reduce moisture content and temperature variations of the rice. Most aeration is controlled by manually turning fans on or off. The guidelines for when to aerate are pretty loose, so the benefits of aeration may not be seen by every farmer.”
Bins are also typically fumigated during storage to control insect infestations in the rice. Howell said many fumigants are under review by the U.S. Environmental Protection Agency and may not be available in the future. Cooling the rice with proper aeration can reduce the need for fumigation.
“Certain temperature thresholds inhibit insect activity,” he said. “Temperatures below 60 degrees will stop the adult insects. Below 45 degrees will have an impact on their eggs.”
Howell documented cooling time and the survival of caged insects in both manually aerated bins and automatically aerated bins. “Temperature was reduced much more quickly in the automatic bins and none of the insects survived for more than 12 weeks,” he said. “In the manually-controlled bins, 25 percent of the insects survived.”
Howell said the automatic controllers are relatively inexpensive and can easily be added to a standard storage bin setup. Commercial controllers are available, but the controllers used in his study were built from readily available parts. In 2000-01, the first year of this project, the controllers consisted of a humidistat and thermostat combined to aerate at preset conditions. Last year, he added a feedback sensor that monitored the rice temperature and prevented re-warming of the rice.
“We like to take advantage of cool weather to get the rice to 40 degrees as quickly as possible,” he said. “The feedback sensors prevented the fans kicking on when the weather warms up and raising the temperature and humidity of the rice.”
He said rising and falling humidity is best avoided because it could lead to kernel fissures.
“Rice quality is an important factor when a producer decides whether or not to store rice on-farm,” Howell said. “That's an important element of our research, and we found quality was consistent with both manual and automatic aeration regimes.”
He said some producers store their rice on the farm because it offers flexibility for marketing and may save the expense of commercial rice drying, but maintaining the quality of their crop is important. His research shows automated aeration offers superior protection and cost savings during on-farm storage.
“Reduction of insect survival in the automatic bins means reduced need for fumigants, cutting costs for farmers and increasing the degree of safety for rice storage,” Howell said. “Pesticide levels in rice are low, but they can be reduced further by reducing or eliminating fumigation in storage bins.”
Fred Miller is science editor for the Arkansas Agricultural Experiment Station. e-mail: firstname.lastname@example.org.