Effects of Regulated Deficit Irrigation on 'Clementina de nules' citrus trees growth, yield and fruit quality effects.

Abstract

[EN] An experiment on Regulated Deficit Irrigation (RDI) was performed during 1997 and 1998 in a drip-irrigated Clementina de Nules/ Carrizo Citrange orchard planted in 1985 in Moncada (Valencia, Spain). Treatments consisted of a control, irrigated during the whole year at 115% of crop evapotranspiration measured in a weighing lysimeter (ETlys) and RDI treatments, where irrigation was reduced at different levels and duration after `June drop¿. The RDI treatments studied were: 25%-J, 50%-J, 50%-J+A, 75%-J+A, 50%-A-O, and 75%-J-O where the percentage is the fraction of ETlys applied during the RDI period and the letters are the month initials (July, August, etc.) indicating the duration period. An additional treatment, denominated 50%-Year, was irrigated at 50 % ETlys during the whole year. The effects of the treatments on yield and fruit quality in relation to tree water status (predawn psi.lc.gif a, and midday psi.lc.gif md, leaf water potential) show large differences of sensitivity to water stress according to the phase of fruit development. The initial stages of fruit enlargement, which in our conditions take place during July and August, are the ones less affected by moderate water stress as fruits can have compensatory growth afterwards. Thus, RDI treatments during July and August allowed water savings between 6 to 22% without affecting yield or its components, nor fruit quality, providing that a threshold value of psi.lc.gif a ¿1.2 MPa was not surpassed. However, similar or lower levels of RDI during September and October produced significant reductions in fruit size and external peel disorders (creasing) in a large proportion of the fruit that decreased their quality and price. Creasing occurred especially in 1998 and exclusively in the 50%-A-O treatment, where minimal psi.lc.gif a values were ¿0.71 MPa and ¿1.5 MPa in 1997 and 1998, respectively.