Issue link: http://read.dmtmag.com/i/108963
Irrigation trees. Wang and Gartung found that midday canopy-to-air temperature differences in the water-stressed trees were in the 10 to 15��F range, consistently higher than the 3 to 4��F range found in the trees not water stressed. To see if data from the sensors were meaningful, Wang used a pressure chamber to measure stem water potential to compare tree stress to sensor data. He found a correlation of about 70 percent between pressure chamber leaf measurements and the canopy to air temperature differences. ���Seventy percent correlation is not perfect, but it���s close and gives us some confidence that the sensor can be used to tell growers what���s going on in the trees,��� he said. ���It means the temperatures obtained from the sensors could be a reasonable indicator of plant stress.��� In the next phase, the scientists are focusing on identifying specific levels of water stress that peach trees can tolerate and identify relationships between stress and canopy temperatures. The sensors, which are commercially available for around $600 to $700, will be tested in irrigation scheduling to see if the technology is viable for commercial orchards. ��� Photo by Dong Wang Orchard-Rite�� Wind Machines ��� www.orchard-rite.com ���The Orchard-Rite crew is great to work with.��� Dong Wang is testing infrared temperature sensors, like this one, in peach orchards to measure water stress. minimize fruit defects from the deficit irrigation. While some deficit irrigation strategies shut tree growth down completely by not watering for a couple months, in the USDA study they maintained an even amount of stress until after harvest, which helped to minimize fruit defects. One of the reasons deficit irrigation has not been adopted more widely by growers is because it has a small margin of error for irrigation timing. That���s where the infrared temperature sensor comes in��� as a potential tool to help growers decide when to irrigate. Sensors USDA agricultural engineer Wang and colleague Jim Gartung, also based in Parlier, are evaluating the use of infrared sensors and thermal technology to assess plant water stress and help growers know precisely when to schedule irrigation. Infrared sensors, around since the 1970s, have been used in cotton and other crops to measure plant health. In the two-year study, 12 infrared temperature sensors were installed in the same peach orchard subjected to deficit irrigation to measure midday canopy and surrounding air temperatures. When trees are water stressed, the stomata begin to close, and less heat is carried away by water vapor transpiring from the leaves. While stomate closing helps the tree conserve water, it also results in a warmer tree and adds to the water stress. Wang said that dry, waterstressed leaves have higher temperatures than a tree with normal transpiration. ���The infrared sensors measure the temperature of the leaf canopy, which reflects the overall thermal footprint of the tree,��� he said. The scientists calculated a crop water stress index based on the differences between tree canopy temperatures and surrounding air temperatures. Higher index numbers indicated more stressed www.goodfruit.com have been farming since 1974, and currently grow 70 acres of cherries. Last year, we put in two Orchard-Rite�� Wind Machines, giving me frost protection on about 40-45 acres. We had a very cold, wet spring. These wind machines were very bene���cial. I Because of our Orchard-Rite�� Wind Machines, we actually had our best crop in what would normally be the poorest-producing portion of the orchard. We are installing two more wind machines this year. The Orchard-Rite crew is great to work with. Anytime I���ve called for information or assistance, they have been Johnny-on-the-spot. Don Nusom Gervais, Oregon Get the Orchard-Rite�� story from your nearest representative: 1615 W. Ahtanum ��� Yakima, WA 98903 ��� 509-248-8785, ext. 612 For the representative nearest you, visit our Web site: www.orchard-rite.com GOOD FRUIT GROWER FEBRUARY 15, 2013 29