USE OF STEM DENDROMETERS AS INDICATORS OF WATER STRESS IN DRIP-IRRIGATED CITRUS TREES

Stem diameter changes of drip-irrigated “Clementina de Nules” citrus trees were recorded continuously during 1994 using LVDT dendrometers in four to six trees per treatment in a well-irrigated (Control) treatment and in three water stressed treatments.
The stress treatments were:

1. irrigation during the whole year at 50% of the evapotranspiration measured in a weighing lysimeter (S50);

2. suppression of irrigation during 1 March to 25 July (S1)

3. during 14 June to 7 September (S2).

During the rest of the year treatments S1 and S2 were irrigated like the Control.

Two parameters were obtained from the dendrometer readings:

1. Amplitude of daily contractions (ADC),

2. Evolution of daily maximum stem diameter (DM)

and they were compared to leaf water potential measurements performed at dawn (^p). The ADC values observed varied with the evaporative demand and were highly variable both between trees (typical C.V. around 20 to 30%) as well as between different days in any treatment.
Maximum ADC for the Control trees was about 350 μm.

At the beginning of water stress ADC values on the severely stressed trees (S1 and S2) were in most occasions significantly higher than those for the Control trees and the differences increased as stress progressed.
The trend reversed before rewatering, suggesting a depletion of the tree water storage.
When irrigation was reassumed ^P increased quickly and stem growth increased also with their ADC values becoming similar to those of the Control in treatment S2 or even lower than them in treatment S1. In treatment S50, ADC also became significantly higher than in the Control during the summer months when stem growth stopped and minimum ^P values were reached.

The evolution of DM appeared more clearly related to water stress development and the inflexion point in the different stress treatments occurred at ^P values of about -0.6 to -0.8 MPa.

The results obtained indicate that the evolution of DM can be used as an index of water stress in citrus.

II International Symposium On Sensors in Horticulture

C. Ginestar, J.R. Castel

Citrus clementina, water stress, leaf water potential, growth

https://doi.org/10.17660/ActaHortic.1998.421.22