Assessment of peach tree responses to irrigation water deficits by continuous monitoring of trunk diameter changes

Continuous monitoring of trunk diameter and of sap flow were investigated to evaluate and characterize tree responses to irrigation water deficits in peach trees (Prunus persica (I,.) Batsch 'O' Henry'). A gradual reduction of irrigation during a three-week period followed by a 17 d recovery was applied to field-grown (SF) and lysimeter-grown (SL) trees. Trunk-diameter change (TDC) measurements and maximum daily trunk shrinkage (MDS) were compared with predawn leaf water potential (PLWP) and midday stem water potential (SWP). TDC was also compared with sap flow calibrated in a weighing lysimeter. The experimental calibration of sap flow (r = 0.95) in a lysimeter showed a 45% underestimation of tree transpiration with a coefficient of 0.55, similar to values found in other tree species. The reductions of water supply were reflected clearly by MDS which showed differences among treatments after only 4 d of 75% ET application. MDS was closely related to PLWP and to midday SWP in both deficit irrigation treatments, and some hysteresis between TDC and SWP was detected. There was a strong relationship between the relative sap flow (sap flow of stress treatment relative to control values) and the relative maximum daily shrinkage. Both parameters were sensitive to water stress, as their values declined by 60% with the development of stress. The relationship between sap flow and TDC shows a hysteresis loop whose shape depended on the stress level. As stress developed, the divergence between MinTD (time of day at which minimum TD was reached) and MaxET (time of day when maximum lysimeter evapotranspiration, ET, was attained) increased. It appears that automated trunk diameter measurements provide a precise irrigation management method for the improvement of irrigation scheduling of peach trees.