Variable effects on tomato (Lycopersicon esculentum(L.)) yield were found in irrigation trials carried out in five seasons from 1973–74 to 1980–81. Only in one season was there a consistent positive response to irrigation; this was the season when soil moisture deficit was highest. The causes of the general lack of an irrigation response were not identified in this study; but observations suggested that the crop's water requirements were being supplied by subsurface water as well as rainfall, irrigation, and soil moisture storage in the 0–430 mm depth (A and B horizon). The subsurface water could have been supplied either by upward flux or by deep rooting. Further investigations are needed to clarify the character of tomato rooting systems and the contribution of upward flux from a water table to the root zone water economics.