A Latin Square design was used to determine effects of undertree irrigation on orchard temperatures during freezes. Plots (40 × 40 m) in a tart cherry orchard included 72 trees. Water was applied at 0, 125, 250 and 380 (± 5%) liters/min. Four meter towers held shielded thermocouples at 1, 2, 2.5, 3 and 4 meters. Thermocouples were monitored at 10-second increments using a Campbell Scintific CR10 micrologger. AM32 multiplexers switched between the 96 thermocouples involved. An IBM AT compatible computer retrieved and stored data from the micrologger at 10-minute intervals. The data acquisition system was activated shortly after midnight and operated continuously until after sunrise on three near-freeze nights. No significant heating effect was present at any water level. On one of the nights, a refrigeration effect was documented.
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