THE EFFECT OF DIFFERENT IRRIGATION RATES ON KIWIFRUIT GROWTH AND CROPPING

Irrigation experiments using micro-sprinklers were carried out to determine the effects of water status on fruit development and crop load. Three irrigation treatments of 36, 63 and 100% evapotranspiration (ET) were applied in young kiwifruit vines, using a dry treatment as a control. Pre-dawn leaf water potentials (LWP's) were used as the index of water stress, using a pressure chamber. Volumes of labeled fruit were measured by water displacement in a graduated cylinder. Fruit development was directly related to water availability. There were significant differences (p<0.05) among the rates applied in the LWP's and in the fruit volumes, since the sixth week after full bloom. However, there were not significant differences (p<0.05) between the dry and the 36% ET rates. Pre-dawn LWP from water stressed vines was <-0.1 MPa, whereas the 100% ET irrigated vines was -0.02 MPa. These vines gave higher yield and fruit size. According to these results and the climatology of Asturias, it is recommended to irrigate with the 100% ET. Special care must be taken concerning the water requirements in the period beginning six weeks after full bloom, in order to optimise the final fruit size.