The 2011 ASHS Annual Conference

The scheduling and recommendations for citrus irrigation is primarily based on soil moisture status and estimated daily water use during the growing season. However, water use of citrus trees is altered differently upon exposure in both long and short-term cold temperature and is independent of soil moisture and evaporative demand. Therefore, recommendations for winter may not be appropriate. Our hypothesis is that irrigation recommendations based on mean winter temperatures may not be appropriate for periods of cold weather when citrus irrigation requirements are lower. Three experiments were conducted in two growth chambers with the primary objective of determining water use of ‘Hamlin’ sweet orange in full cold-acclimating temperatures and alternate cold and warm temperatures for 10 and 3 days, and 3 and 10 days; respectively. Results showed that although the plants were well-watered, the fully cold acclimated plants used nearly 65% less water than the control. Reduction of water use by cold-treated plants over control plants was 43-64% and 48-60% upon exposure to alternate 10 days cold and 3 days warm and alternate 10 days warm and 3 days cold temperatures, respectively. The reduced water use of cold-treated plants coincided with reduced stomatal conductance, reduced stem water potential, and increased root resistance for water uptake. Effective irrigation scheduling based on accurate crop demand could save considerable quantities of water in citrus production, while providing adequate water to maintain citrus yield and fruit quality.