Vitis 44 (3), 117–125 (2005) Effects of partial root-zone drying irrigation on cluster microclimate and fruit composition of field-grown Castelão grapevines T. P. SANTOS1), C. M. LOPES1); M. L. RODRIGUES1), C. R. DE SOUZA2), J. M. RICARDO-DA-SILVA1), J. P. MAROCO2), J. S. PEREIRA1) and M. M. CHAVES1),2) 1) Instituto Superior de Agronomia, Universidade Técnica de Lisboa, Lisboa, Portugal 2) Laboratório de Ecofisiologia Molecular, Instituto de Tecnologia Química e Biológica, Oeiras, Portugal Summary effects on wine quality. Due to the severe water stress in the last decade irrigation became an increasingly common in The partial root-zone drying (PRD) irrigation tech- central and southern parts of the country where high poten- nique has been proposed for viticulture as a possible way to tial evaporation and low rainfall dominate during the grow- save water without compromising yield. Half of the plant ing season. It is now considered important for stabilizing root system is slowly dehydrating whereas the other half is yield and to warrant vine longevity. irrigated; after about two weeks the opposite side of vines is Future climate scenarios suggest drier and warmer con- irrigated. A PRD irrigation system (50 % of the crop ditions for most of southern Europe, with longer dry sum- evapotranspiration - ETc) was installed in a vineyard (Vitis mers and more severe plant water deficits (SCHULTZ, 2000; vinifera L. cv. Castelão) in Southern Portugal and com- MIRANDA et al. 2002). With enhanced pressure on water re- pared with two other irrigation systems, deficit irrigation, sources, the increasing demand for vineyard irrigation will DI (50 % ETc) and full irrigation, FI (100 % ETc), as well only be met if there is an improvement in the efficiency of as with non-irrigated vines (NI). Water was applied twice a water use. This goal can be obtained by deficit drip-irriga- week, from fruit set (mid-June) until one week before har- tion, including partial root-zone drying techniques (LOVEYS vest (September 3). While FI vines remained well watered et al. 2000). during the ripening period, a severe water stress developed Regulated Deficit Irrigation (RDI) is one of the most in NI plants. PRD and DI vines exhibited mild water deficits frequently used drip-irrigation strategies in vineyards with during the same period. A significant decrease in vegeta- the aim to balance grapevine vegetative and reproductive tive growth (shoot weight, pruning weight, leaf layer number growth by applying less than the full vineyard water use at and percentage of water shoots) was observed in NI and specific periods of the growing season (CHALMERS et al. PRD vines when compared to DI and FI. In denser canopies 1986; MCCARTHY 1997; BATTILANI 2000; DRY et al. 2001). One (FI and DI) berry temperature was always lower than that of of the main objectives of RDI on red-wine cultivars is to the more open ones (NI and PRD). The higher degree of reduce berry size, leading to an increase of the berry skin/ cluster exposition in PRD and NI had a positive influence flesh ratio and thus to an improvement of fruit quality. The on berry composition due to temperature and incident ra- management of RDI is, however, not easy. A major difficulty diation, leading to higher concentrations of anthocyanins is the need for a reliable soil water monitoring system in and total phenols in the berry skin compared to DI and FI order to avoid the risk of severe water stress in periods with vines. Irrigation did not significantly affect berry sugar extreme temperature events (GOODWIN and JERIE 1992). accumulation and pH in berries. Compared to FI, PRD and An irrigation technique called Partial Root-Zone Drying DI treatments water use efficiency (the amount of fruit pro- (PRD) was developed, allowing to control plant growth and duced per unit of water applied) was doubled since at the transpiration avoiding severe water stress periods that can same yield the amount of water applied, was reduced by occur in RDI (DRY et al. 1996, DÜRING et al. 1997, LOVEYS 50 %. et al. 2000). With the PRD technique part of the grapevine root system is slowly dried and while the remaining roots K e y w o r d s : berry temperature, canopy microclimate, are exposed to wet soil. Thus, roots of the watered side fruit quality, Vitis vinifera L., irrigation, partial rootzone drying, maintain a favourable plant water status, while dehydrating yield. roots will produce chemical signals that are transported to A b b r e v i a t i o n s : DI: deficit irrigation, ETc: crop the shoots via the xylem and will hypothetically control veg- evapotranspiration, ETo: potential evapotranspiration, FI: full ir- etative vigour and stomatal aperture (DODD et al. 1996; Dry rigation, LLN: leaf layer number, NI: non irrigation, PRD: partial et al. 1996). In recent years much information obtained un- rootzone drying, PPFD: photosynthetic photon flux density, T : b der controlled conditions have provided evidence for a re- berry temperature, WUE, water use efficiency. duction of growth and gas exchange of plants in drying soil, without shoot water relations being affected (DAVIES et al. Introduction 1994; Liu et al. 2003). There is an extensive experience with PRD irrigation of For a long time, vineyard irrigation was uncommon in grapevines in Australia (LOVEYS and DAVIES 2004). In most wine production in Portugal, because of possible negative cases, PRD resulted in a better control of vegetative growth, Correspondence to: Dr. M. L. RODRIGUES, Instituto Superior de Agronomia, Universidade Técnica de Lisboa, Tapada da Ajuda, 1349-017 Lisboa, Portugal. E-mail: [email protected] 42 118 T. P. SANTOS et al. providing an adequate exposure of clusters to sunlight and I r r i g a t i o n a n d e x p e r i m e n t a l d e s i g n : saving water without detrimental impacts on the quality and Irrigation was applied with drippers, two per vine, and inde- yield (LOVEYS et al. 2000). In addition to a favourable bal- pendently controlled and positioned 30 cm from the vine ance between vegetative and reproductive growth the lower trunk, at both sides of the row. Water was applied according vigour in PRD allows a more open canopy and, consequently, to crop evapotranspiration (ETc), estimated from the poten- influences the light environment within the fruit zone. The tial evapotranspiration (ETo), which was calculated from beneficial effects on berry composition and metabolism are Class A pan evaporation and using the crop coefficients well documented, usually improving fruit colour and anthocy- (Kc) proposed by PRICHARD (1992). Each irrigation treatment anin concentrations in red varieties in addition to a rise in was checked by a time clock-valve-assembly to control wa- total phenols (CRIPPEN and MORRISON 1986 a, b, SMART et al. ter supply. The treatments were: fully irrigated (FI, minimum 1988, DOKOOZLIAN and KLIEWER 1996, KELLER and HRAZDINA water deficit, 100 % of the ETc, half of the water amount 1998, SPAYD et al. 2002). An excessive cluster exposure may supplied by drippers, 4 l·h-1 to each side of the vine); deficit lead, however, to supra-optimal berry temperature with det- irrigated (DI, 50 % of the ETc, half of the amount of water rimental effects on grape berry composition. In fact, while in supplied to each side of the row with 2 l·h-1 by drippers); most wine-producing regions a high grape exposure is ben- partial root drying (PRD, 50 % of ETc periodically supplied eficial, in some warm regions the high temperature of fully to only one side of the vine by drippers, 4 l·h-1, while the exposed berries can reduce or even inhibit the synthesis of other side tried); non-irrigated (NI, rainfed). In PRD the first anthocyanins (COOMBE 1992, HASELGROVE et al. 2000, change of the irrigation side of the vine was done after BERGQVIST et al. 2001, SPAYD et al. 2002). 1 month and then alternating sides every 15 d. Vines were The aim of the present study was to evaluate the re- watered twice a week, from fruit-set (mid-June) until one sponse of Castelão grapevines to differences in soil water week before harvest (September 3). The total amount of water availability in the root system as a consequence of different supplied to FI plants was 196.8 mm (493 l per vine). The PRD irrigation techniques under field conditions. Two objectives and the DI vines received half of this amount. were specifically addressed: (1) The effects of PRD on plant The experimental design was a Latin square with 4 treat- growth and canopy density. PRD plants were compared with ments and 4 replications per treatment. Each replicate (plot) vines that were rainfed (NI), fully irrigated (FI) or that re- had 3 rows with 15 to 20 vines each and all the measure- ceived the same amount of water as PRD but distributed to ments were made in the central row. both sides of the vines (DI). This treatment is important P l a n t a n d s o i l w a t e r r e l a t i o n s : Pre-dawn because earlier studies compared PRD with a system where leaf water potential (Ypd) was measured weekly from the be- the water given to each plant was twice as much as in PRD ginning of berry development (pea size) until harvest (sec- (LOVEYS et al. 2000). Field trials where PRD was compared ond week of September). Measurements were carried out on with a control receiving the same amount of water are still one adult leaves of 6 replicate plants of each treatment and scarce (LOVEYS et al.