Sap flow and water consumptive use in cherry trees irrigated or not irrigated under trickle irrigation.

Hydric behaviour of cherry trees, irrigated under trickle irrigation and non-irrigated (table I), are investigated. Irrigation rate is controlled by tensiometry. Sap fluxes in cherry trees are measured by a thermal method, hourly branch diameter variations by micromorphometry, and water soil transfer by neutronometry and tensiometry (fig I). It has been shown that: i) a general heterogeneity of sap fluxes is present in different sectors of a cherry tree trunk section (fig 2; table II). The heterogeneity is closely correlated and induced by the spatial and temporal heterogeneity of different soil sector wetting in relation to local root bundles (fig 3); under irrigation, the ratio between extreme fluxes, measured in a trunk section, is close to the ratio between the two sources of water in the soil, irrigation and the natural soil water contribution; ii) sap flow in trunks, whatever the hydric conditions may be, is essentially a function of instantaneous availability of soil water, the effect of ETP being virtually negligible; iii) a heterogeneity of diameter microvariations is present in branches of non-irrigated trees and not in irrigated trees (figs 4 and 5). It has been concluded that preferential flow pathways exist in the soil-plant system. The relative participation, in time, of internal water tree reserves and sap flows to evapotranspiration (figs 6 and 7), and the existence of water stress in trees or the satisfaction of their real water requirements as a function of different water supplies have also been shown. It is concluded that methodology used is not only a good tool for characterising water relations and water stress of trees but also for upgrading trickle irrigation scheduling of cherry tree orchards: especially if these measures are continuous and self-acting.