Use of maximum trunk diameter measurements to detect water stress in mature 'Arbequina' olive trees under deficit irrigation

Olive is one of the fruit tree species for which measurements of the trunk diameter variation (TDV) has shown a lower potential both for monitoring water stress and for scheduling irrigation. This is particularly true in the case of old, big olive trees with heavy fruit load. Fernandez et al. (2011, J. Environ. Exp. Bot. 72, 330-338) observed that the daily difference for maximum trunk diameter between deficit irrigated 'Manzanilla' olive trees and control trees growing under non-limiting soil water conditions, termed D-MXTD, is more sensitive and reliable for detecting the water stress of the trees than other widely used TDV-derived indices. However, they considered their results as preliminary because of the lack of replications. The aim of this work was to evaluate the usefulness of the D-MXTD index tot detecting plant water stress in an orchard with 12-year-old 'Arbequina' olive trees with heavy fruit load. The performance of DMXTD for detecting water stress of the trees was compared to that of the signal intensity for the maximum daily shrinkage (SI-MDS) derived from the same TDV records. Results showed that SI-MDS was not useful for indicating the water stress of the trees. On the other hand, the dynamics of D-MXTD mimicked those of the soil and plant water status. Four instrumented trees per treatment (replicates) were enough to reduce the uncertainty of the TDV measurements to a reasonable level. Our results show that D-MXTD is a useful index to detect the onset, and severity, of water stress in mature 'Arbequina' olive trees with heavy fruit load. They also suggest a potential of D-MXTD for scheduling low frequency deficit irrigation strategies. (C) 2011 Elsevier B.V. All rights reserved.