Issue link: https://read.dmtmag.com/i/622402
www.goodfruit.com Good Fruit Grower JANUARY 15, 2016 35 then counted, weighed and mechanically sized the remainder of the crop. Stress that occurs one summer can affect developing buds for the following year's crop. As a result, the researchers noted that trees that received only 25 per- cent ET had significantly reduced yields and quality the second year. The fruit also had more deformities. Because of the negative impact 25 percent ET irrigation had on the crop, Ayars said he would not recommend that practice to growers. But by cutting later-season irrigation in half, growers could see 50 percent savings in postharvest water use with no significant differences in yield or defor- mities compared to trees that received full ET. Wang, research leader with the cen- ter's Water Management Unit, continued work in the same peach orchard to exam- ine whether infrared sensors and thermal technology could be used to characterize plant water stress based on plant canopy temperature. As temperatures rise, loss of water vapor through leaf pores — or stomata — cools the plant. When water loss from the leaves exceeds what the plant can take up from the soil through roots, the stomata shut down and the plant heats up. The temperature of the plant has been used previously as a measure of the stress in some field crops. Thermal technology and hand-held infrared sensors were used by cotton growers in the 1970s to monitor crop health. Wang and ARS agricultural engineer Dr. Jim Gartung placed infrared temperature sensors above the tree canopy in the orchard. In a well-irrigated orchard, tree temperatures can be about 2°C — about 35°F — lower than the ambient air temperature, Wang explained. But as trees become stressed, the difference may reverse, with canopy temperatures exceeding ambient air temperature by more than 4°C (about 39°F) under extreme conditions. These trials compared thermal technology readings to soil moisture sensor data and midday stem water potential readings from a pressure chamber to determine how well the results correlated. The researchers found canopy temperatures that were approximately 2°C warmer than the surrounding air correlated to about a 50 percent deficit irrigation while fruit size was not affected, Wang said. In his latest research, Wang has begun working with a canning peach grower near Kingsburg to gain a better understanding of the water requirements of a tree's various growth stages. The project differs from the work at Parlier because it involves a later- season canning peach variety. It also will examine how a grower's typical irrigation regime matches up against the tree's water requirements. "One of the things I think is pretty common in California is most growers don't have water meters for surface irrigation," Wang said. Instead, many growers know the gallons-per-minute flow and run water for a set number of hours. Good water management requires an accurate measurement of applied water and that requires precise measurement of flow, he said. • Photo courtesy AgriculturAl reseArch serVice An infrared thermometer mounted on a pole measures peach tree canopy temperatures under regulated deficit irrigation. Canopies of stressed trees have a higher temperature than nonstressed trees. Rears Manufacturing Company 800.547.8925 A heartfelt thanks to all who contributed to the Washington Apple Education Foundation 2015 Friendraising Drive James Foreman of Wenatchee took home the silent auction prize, a Rears OMF756 orchard flail. James' winning bid boosts scholarship and grant pro- grams: WAEF raised $39,000 at the 2015 WSHA show. Thank You! John Klefeck of Royal City was the winning ticket holder for the WAEF benefit raffle prize: a 2016 Rears TTN Powerblast sprayer. John, at right, is pictured here with Mike Rear of Rears Manufacturing Company.