Spatial and Temporal Resolution Requirements For Real-Time Temperature Measurements in Perennial Crops.
Eileen M. Perry, Pedro Andrade, Jose Chavez, and Francis Pierce. Washington State Univ, Irrigated Agriculture Research & Extension Ctr, 24106 N. Bunn Rd, Prosser, WA 99350
Growers of high value perennial crops must make management decisions based on conditions that can vary on spatial and temporal scales of meters and minutes. For example, tree fruit growers expend tremendous effort and cost to protect against frost damage to sensitive flowers and buds as critical changes in temperature can occur within minutes. While 15 minute averages of weather station data may be adequate for some management issues such as irrigation scheduling, other management issues such as temperature monitoring for frost protection require data with high spatial and temporal resolution. This study evaluated small but critical temperature changes during frost events associated with a reflective mulch ground cover installed to benefit fruit growth and maturation. Multiple temperature sensors were installed in an apple orchard (Malus domestica Borkh. cv. 'Granny Smith') in rows with and without the reflective mulch to obtain high spatial and temporal resolution data. Air temperature was measured at one minute intervals for several heights in the canopy as well as for the blossom temperatures and shallow soil temperature. Temperature differences between the two ground cover treatments for the same height changed throughout a 24 hour period. Flower temperature differences between the treatments fluctuated, although flower temperatures were consistently colder in the mulch site during freezing conditions. Averaging one minute temperature measurements to a 15 minute interval reduced or eliminated the treatment differences. The results demonstrate that in situ measurements can be important for extreme events (such as frost protection). Temperature fluctuations can occur over short periods that go undetected when measurements are made outside the actual canopy environment, and/or after averaging over longer periods such as the traditional 15 minute intervals.