specific length during the growing season. Three trellising designs were used to ob- tain three distinct shoot inclinations within Type of Trellis Affects Radiation the vineyard. The positioning of shoots on trellises resulted in canopies that were 1) po- Absorption and Must Composition but sitioned vertically (vertical canopy), 2) po- sitioned in a “V” pattern with sides inclined not Yield of ‘Petite Sirah’ Grapes 60o from horizontal (inclined canopy), and 3) inclined toward the vineyard floor (stan- T.H. Morsil, A.D. Matthias2, and J.L. Stroehlein3 dard canopy). The vertical canopy was ob- Department of Soil and Water Science, University of Arizona, Tucson, tained by attaching cordons and shoots to a vertically arranged three-wire trellis. The AZ 85721 lower wire was used for cordon support, and Additional index words. radiation balance, PAR, wine, vineyard, Vitis vinifera the middle and upper wires were used to sup- port shoots. Spacing between lower and Abstract. The effects of trellising on absorption of photosynthetically active radiation middle wires was 0.46 m, and spacing be- (PAR, 400- to 700-nm wavelength) by foliage and fruits, on fruit composition, and tween middle and upper wires was 0.58 m. yield were studied in 1988 under semi-arid conditions using field-grown Vitis vinifera This canopy was designed to provide in- L. ‘Petite Sirah’ grapevines in a mature vineyard. A vertical inclination was obtained creased PAR absorption and fruit shading near o by attaching shoots to a vertically arranged three-wire trellis; 60 shoot inclination solar noon when incoming radiant energy from horizontal was obtained by attaching shoots to a “V-type” Tatura trellis; a stan- fluxes were greatest. The inclined canopy dard two-wire trellis (control) was used in which shoots attached to the upper wire was supported on a “V-type” Tatura trellis. were permitted to orient downward to the vineyard floor. PAR absorption by foliage This trellis consisted of five wires for sup- during mid-morning to mid-afternoon periods was highest in the standard trellis and port of cordons and shoots. A lower wire lowest in the Tatura trellis. PAR available for absorption by fruits was lowest in the was used to support cordons. Four upper wires standard trellis and highest in the Tatura trellis. Analysis of fruit composition at harvest were attached to the ends of stacked 0.38- o revealed that total dissolved solids ( Brix) was significantly higher for berries from the and 0.76-m double crossarms for support of Tatura trellis than for the vertical trellis or the control. The Tatura trellis resulted in shoots. Spacing between crossarms was 0.58 the highest alcohol content of wine. Per-vine yields did not differ significantly among m. The inclined canopy was used to study the three trellis systems. the effect of decreased PAR absorption by foliage and decreased shading during midday Trellis design is an important factor that in- We present preliminary results from a field periods. The standard canopy (control) was fluences the physiological and management study in Arizona to determine the effects of supported on a standard two-wire trellis with aspects of grapevines (Smart, 1988; Smart et three trellising systems on absorption of pho- a 0.46-m spacing between the lower and up- al., 1982, 1985; Van den Ende, 1984). De- tosynthetically active radiation (PAR) by fo- per wires. Shoots were attached to the upper signs in which excessive shading of fruits by liage and fruits, fruit composition, and yield wire and were permitted to orient downward foliage occurs have generally reduced fruit of mature ‘Petite Sirah’ grapevines. This study toward the vineyard floor. This orientation quality and yield. A two-wire (Geneva Double was motivated by the need to determine op- resulted in a relatively dense foliage config- Curtain) trellis design increased ‘Concord’ grape timal shoot positioning for the production of uration that nearly enveloped the fruits and yields by as much as 90%, relative to a single- wine grapes in a hot, semi-arid climate, such provided nearly total fruit shading from di- wire (Kniffin) design, as a result of improved as Tucson, because, to our knowledge, noth- rect sunlight throughout the day. The stan- leaf and shoot exposure (Shaulis et al., 1966). ing has been published about the effect of dard trellis is commonly used in vineyards The yield of ‘Crouchen’ grapes was increased shoot positioning on productivity of grapes in the southwestern United States. Cordon up to 30% due to trellis widening from 0.3 to grown in such a climate. Growth of wine height above ground for all three canopies 1.4 m (May et al., 1976). Improved fruit ex- grapes under high air temperatures and in- was » O.9 m. Establishment of vertical and posure with four- and six-wire trellising sys- tense midday solar radiant energy fluxes re- inclined canopies occurred during Mar. 1988. tems increased ‘Cabernet Sauvignon’ yields by quires efficient configuration of the vine A completely randomized design was used, 45% and 48%, respectively, relative to the yield canopy to achieve optima1 radiation absorp- consisting of the three treatments. Each can- from a standard two-wire trellis (Steinhauer tion by foliage, fruit shading, and fruit tem- opy treatment was replicated eight times, with and Bowers, 1979). Reynolds et al. (1986) perature conditions within the canopy. each replicate containing three vines. Data found that the most exposed ‘Seyval blanc’ Excessive shading by foliage or excessive from the two outer (border) plants within a fruit had the highest pH levels, in addition to exposure to intense radiant energy may re- replicate were not collected; thus, data from the highest oBrix and tartrate content, and the duce fruit quality. only the middle vine were used in the study. lowest titratable acidity. Reynolds et al. (1986), The experiment was conducted during the Components of the PAR budget of each however, reported no significant wine quality 1988 growing season at a 0.7-ha vineyard at type of canopy were measured on several differences due to differences in fruit expo- the Univ. of Arizona Campus Agricultural clear days during the season using a 80-cm- sures. Recently, Patterson and Zoecklein (1990) Center, Tucson, using lo-year-old ‘Petite long, Decagon Model SF-80 Sunfleck Cep- showed that increased radiation penetration due Sirah’ grapevines. This cultivar was chosen tometer (Decagon, Pullman, Wash.). Mea- to shoot positioning and removal of nonfruitful because it generally produces wines with ad- surements of the descending and ascending shoots resulted in superior fruit (i.e., reduced equate color and flavor in warm climates PAR (µmol·m-2·s-1) components of the malate and potassium) relative to other treat- (Mielke et al., 1980). The vines were grown budget were made at 0.5-h to 2-h intervals, ments in ‘Norton’ grapes. in Brazito sandy loam soil, which is classi- typically from mid-morning to mid-after- fied as mixed thermic Typic Torrifluvents. noon, and were used to calculate the PAR Received for publication 17 Dec. 1990. Accepted The vines were basin-irrigated at » 3-week absorbed by foliage (APAR) for each canopy for publication 28 Aug. 1991. Journal article no. intervals. Spacing was 2.1 m between vines, design. Instantaneous APAR was calculated 7308 from the Arizona Agr. Expt. Sta, The cost with rows 3.3 m apart. Rows were oriented using Eq. 1 from Gallo and Daughtry (1986) of publishing this paper was defrayed in part by north-south. Before 1988 each vine had been given here as: the payment of page charges. Under postal regu- trained to a standard two-wire trellis. All vines lations, this paper therefore must be hereby marked APAR = (PARo + RPARs)— advertisement solely to indicate this fact. were spur-pruned in Jan. 1988 to 20 buds/ (TPAR + RPARc) [1] 1Graduate Student. cordon with two cordons per plant. There 2Associate Professor. were » 20 shoots/meter of row and » 130 where PAR, is the PAR flux incident on the 3 Professor. leaves/shoot. Shoots were not pruned to a canopy, RPAR, is the PAR reflected from the soil surface to the canopy, TPAR is the of PAR available for absorption by the fruits. incoming PAR (PARo) was absorbed by the PAR transmitted through the canopy, and As done with APAR, FPAR was also con- foliage in the standard canopy, thus provid- RPARc is the total PAR reflected from the verted to daily (integrated) values. Also, ing relatively uniform shading of fruits at the canopy and the soil. PARo and RPARc were FPAR was expressed as a fraction of PARo base of the canopy. This high percentage of measured at » l m above the canopy using on a daily basis according to: FPAR' = midday PARo absorption by foliage may in- the leveled ceptometer facing either upward FPAR/PARo. Only FPAR' and APAR' val- crease photosynthesis and growth in the or downward, respectively. RPARs was ues are presented. standard canopy relative to the others. In measured with the inverted ceptometer at The fruits were harvested 17 Aug. 1988, contrast to the standard canopy, the inclined » 0.2 m above the soil surface. TPAR was which was several days earlier than the nor- canopy absorbed, on average, only » 71% measured by positioning the upright level mal harvest of ‘Petite Sirah’ at the end of of PARo, thus allowing for increased expo- ceptometer diagonally across the canopy at August in Tucson (Mielke et al., 1980). Fruit sure of fruits, and potentially higher fruit about the height of the basal fruits. Ten rep- was harvested early to avoid yield loss due temperatures. Similarly, the vertical canopy licate measurements of each of the four PAR to possible infestation by birds and insects.