Improvements of Relative Indicators of Trunk Diameter Fluctuations in Comparison to Discrete Indicators in the Regulated Deficit Irrigation Scheduling of Olive Trees

Daily cycles of trunk fluctuations are used to measure plant water status. However, the traditional indicators derived from these curves constrains the selection of thresholds. The aim of this work was to evaluate a new indicator based on maximum daily shrinkage (MDS). The experiment was performed in a hedgerow olive orchard at Seville (Spain) in 2025. Trunk diameter fluctuations were characterized by weekly frequencies of the appearance of trunk growth rate values (good and severe). In addition, the indicator reference was defined as the ratio between the MDS signal (normalized from MDS with evaporative demand) and the average MDS signal at the beginning of the experiment. Three irrigation treatments were performed: fully irrigated-control, and two regulated deficit irrigation. Patterns of the trunk diameter fluctuation indicators were compared with discrete measurements of fruit development and water status. Good rates presented an earlier decrease with water stress (33 days before) and a more variable pattern than severe rates. The reference indicator showed the most sensitive pattern with an early effect (10 days before), the greatest number of differences (40 days vs. 22), and a clear read to identify water stress. These relative indicators improved the management of water stress.