Abstract
Abstract Two-year-old ‘Hamlin’ orange trees [ Citrus sinensis (L.) Osb.],on Poncirus trifoliata (L.) Raf. rootstock were used to study the effects of various microsprinkler irrigation rates and spray patterns on trunk temperatures and microclimate during freeze conditions. Irrigation treatments consisted of a factorial combination of two spray patterns (90° and 360°) × three application rates (38, 57, and 87 liters hr −1 ), plus an unirrigated control. All trunks were wrapped with fiberglass insulation. Trunk temperatures were 1° to 5°C higher for irrigated than unirrigated trees, regardless of spray pattern or application rate and were 1° to 2°C higher with the 90° than 360° spray pattern. The 57 and 87 liter·hr −1 rates produced the highest trunk temperatures, although 38 liter·hr −1 maintained trunk temperatures above −2.5°C with air temperatures as low as − 12°C. Outgoing radiation was higher for irrigated than unirrigated treatments during advective freeze conditions only, but air temperature and vapor pressure were unaffected by microsprinker irrigation.