Predawn leaf water potential and soil water content in vertical trellis under irrigated and non-irrigated conditions in Tempranillo grapevines

The relationship between soil water content and predawn water potential for cv. Tempranillo grapevines cultivated under non-irrigated and irrigated co nditions during 4 years (1994-1997) have been investigated. The vines were 7 years old in 1994. Soil water content was measured by the TDR technique u p to the depths of 0.15, 0.30, 0.60 and 1.00 m. Predawn leaf water potentia l was measured throughout the vegetative cycle of the vine. Soil water content decreased throughout the year with the major drop occurr ing from flowering to veraison and reaching the lowest values of about 9 % at harvest. No significant differences in soil water content between non-ir rigated and irrigated plots have been observed. Water content of the 0.3-0. 6 m horizon showed a similar evolution and level as the whole profile. Ther efore, the measurement of the 0.3-0.6 m horizon provides a good estimate of the whole profile. Predawn leaf water potential decreased throughout the season being higher i n the irrigated vines compared to the non-irrigated ones from before verais on until harvest. Predawn leaf water potential increased rapidly with soil water content, but it stayed approximately constant to higher content than 12 %. Predawn leaf water potential resulted to be linearly related to soil matrix potential predawn leaf water potential decreased as well.