Soil water availability and relationship between canopy and roots in young olive trees (cv Coratina)

Trials were carried out in the Basilicata region (41degrees03' N, 15degrees42' E, Southern Italy) using ownrooted plants of the cultivar Coratina planted in 1992 at distances of 6 x 3 m. During 1992, the whole plot (about 7000 m(2)) was irrigated. From 1993 onwards, irrigation was suspended in part of the plot. A representative number of plants during 1992, 1993, 1994 and 1998 was destroyed in order to carry out dry weight measurements on roots and canopy. The ratio between root and leaf dry weight was always greater in non-irrigated plants compared to irrigated ones. Roots explored a soil volume ranged from 0.5 m(3) in the first year to 16.8 m(3) in the seventh year for irrigated plants and from 0.5 m(3) to 13.4 m(3) for non-irrigated ones. The study showed that in deep soil, with a greater capacity for water storage during the rainfall season, limited water supply (220-1350 m(3) ha(-1)) during the first seven years from planting increased canopy growth by 79% compared to non-irrigated plants, but made little difference to root growth. In non-irrigated plants, canopy growth (but not root growth) was drastically reduced, as a defence strategy against water deficit, making for a better root/leaf ratio and consequently greater water availability for leaves.