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Characterisation of water use by grapevines on their own roots or on Ramsey rootstock drip-irrigated


Irrig Sci (1997) 17: 77– 86

? Springer-Verlag 1997

O R I G I N A L PA P E R

I. A. M. Yunusa · R. R. Walker · D. H. Blackmore

Characterisation of water use by Sultana grapevines (Vitis vinifera L.) on their own roots or on Ramsey rootstock drip-irrigated with water of different salinities

Received: 6 May 1996

Abstract Seasonal evapotranspiration (ET) was determined for Sultana grapevines grown on their own roots (Own-rooted) or grafted onto Ramsey rootstock (Grafted), and irrigated with water of three salinity levels – low (0.4 dS m–1), medium (1.8 dS m–1) and high (3.6 dS m–1) – during the 1994/1995 growing season in south-eastern Australia. Transpiration ( T) was determined from sap flux, soil evaporation (Es) with a model, and soil water (S) with a neutron probe. Total ET for the season was similar for both Own-rooted and Grafted, averaging 382 mm. However, Grafted partitioned a mean of 193.5 mm (50.8%) of the ET through T compared to 146.7 mm (38.4%) by Ownrooted. Daily rates of T were generally low and attained peaks of 1.2 mm (9.9 l per vine) for Grafted and 0.9 mm (7.5 l) for Own-rooted in late November, and changed very little until after harvest in February. In contrast to T, the Es rate was consistently higher for Own-rooted than for Grafted from November onwards, and at the end of the season totalled 237 mm for Own-rooted compared to 187 mm for Grafted. Differences between Own-rooted and Grafted in their partitioning of ET into T and Es were associated with their canopy development. Grafted had a higher rate of canopy development than Own-rooted, and in mid-season, the former intercepted about 50% more incident radiation than Own-rooted. The crop factors, i. e. ratio of water use to evaporative demand, based on ET were similar for both vine types with an average seasonal value of 0.25, but when based on T were 0.12 for Grafted and 0.10 for Own-rooted. The ratio of fresh fruit weight to total water used at harvest, i. e. crop water use efficiency (CWUE), based on ET, had a mean of 86 kg mm–1 ha–1 for Grafted and 43 kg mm–1 ha–1 for Own-rooted, and when based on T, was 165 and 115 kg mm–1 ha–1, respectively; however, supplementary data obtained during the 1993/1994 season, indicated a CWUE based on T of 294 and 266 kg mm–1 ha–1 for Grafted and Own-rooted, respectively. Sa-

linity did not have significant effects on canopy development and water use for most of the 1994/1995 growing season. The study shows ET and crop factors for the drip-irrigated grapevines to be much lower than previously reported for this district.

Introduction

Achieving high water use efficiency has become a major issue in sustainable irrigation cropping systems. To develop irrigation practices that harmonise high water use efficiency and avoid over-irrigation, it is imperative to quantify components of the soil water balance. The water balance of an irrigated vineyard can be represented as: ?S = P+I+Gw –Es –T –RO –D (1) in which ?S is the change in the storage of soil water, P rainfall, I irrigation, Gw water contributed to the root zone by the shallow water-table (where present), Es soil evaporation, T transpiration, RO surface run-off and D through-drainage. Since both Es and T are closely linked and difficult to measure separately, they are often combined and quantified as evapotranspiration (ET) or crop water use. However, the contribution to ET from Gw is negligible where the soil is adequately recharged from the top and the perched water-table is of poor quality, while RO is largely avoided with drip irrigation systems (Hillel 1987). Hillel (1987) used the term “technical or irrigation water efficiency” (IWUE), i. e. the ratio of water applied to the root zone to that used for ET, to evaluate the supply and demand of water for an irrigated crop. In the Mallee district of south-eastern Australia, the recommendation is to keep the soil water potential above –40 kPa in the 0.5-m soil profile (Prior and Grieve 1986). Maintaining such a high water potential requires frequent application of water which may lead to over-irrigation, and the magnitude of D could then become the main determinant of IWUE. D can be minimised if water applications are matched to crop requirement, which is commonly

I. A. M. Yunusa ( ) · R. R. Walker · D. H. Blackmore CSIRO Division of Horticulture, Private Mail Bag, Merbein, Victoria 3505, Australia

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achieved using the crop factor (Kc). Doorenbos and Pruitt (1984) defined Kc as the ratio of ET to the potential evaporation (Epot), and recommended Kc values of between 0.2 and 0.7 for grapevines, values similar to those obtained in experimental vineyards in California (Williams et al. 1992). It has been reported that this range of Kc values in the Mallee district maintains the soil water potential above the recommended –40 kPa (Prior and Grieve 1986). However, depending on management practices and environmental conditions, Kc values can fall as low as 0.21 – 0.31 (Van Zyl and Van Huyssteen 1980; Oliver and Sene 1992). Thus, Kc is not constant and fluctuates with weather, irrigation regime and other management options. Hanks (1985), therefore, argued that Kc is of limited application especially where incomplete canopy cover provides little restraint on Es under the high evaporation conditions of arid environments. He proposed the use of a crop coefficient based on transpiration (Kt), i. e. T/Epot. Cultural practices and scion-rootstock combinations strongly influence the growth of grapevines, and would be expected to modify water use. For instance, Sultana vines grafted onto Ramsey rootstock develop larger root systems (Nagarajah 1987) and bigger foliage canopies than ownrooted vines (R. R. Walker, F. Iocono, D. H. Blackmore, unpublished data), and thus would be expected to have high water requirements compared to own-rooted vines. Furthermore, adverse effects of salinity on vine growth and yield have been observed both in the field (Prior et al. 1992 a, b; Walker et al. 1996) and in the glasshouse (Downton 1977 a, 1985; Walker et al. 1981), and the range of factors influencing grapevine response to salinity have recently been reviewed (Walker 1994). The response of vine growth to differences in rootstock or salinity may, therefore, modify seasonal water use and the yield produced per unit of water used, i. e. crop water use efficiency (CWUE). Previous studies on the vineyard water balance in the Mallee district used neutron probe and drainage lysimeters (Prior and Grieve 1986). These methods may be inefficient in quantifying D and T, especially with frequent irrigation and in the presence of a perched water table. In the present study, the water use of vines was obtained by separately determining T, with sap flow sensors, and Es, with a model. The objectives were to determine (1) both daily and seasonal water use by the vines, (2) baselinne Kc and Kt for vines under non-limiting water supply conditions, and (3) to evaluate the effects of rootstock and salinity on water use and CWUE, during the 1994/1995 growing season. The data were supplemented with limited measurements from the 1993/1994 season.

Table 1 Summary of selected physical and chemical properties of the soil profile Parameters Physical a Texture Clay (%) Silt (%) Fine sand (%) Coarse and (%) Chemical b Na (mg l–1) K (mg l–1) Mg (mg l–1) Ca (mg l–1) Cl (mg l–1) EC (dS m–1) pH
a b

Values Sandy loam 22 5 30 22 272.0 12.5 82.0 175.0 406.0 2.4 8.3

Averages for the top 0.3 m of the profile (from Penman et al. 1939) Averages for the top 0.9 m of the soil profile in November 1989 prior to imposition of salinity treatments

The soil at the site is a sandy loam with a 17% clay content, referred to as Coomealla sandy loam (Penman et al. 1939). The soil profile consists of 0.28 m of brown sandy loam at the top which is underlain by light-brown sandy clay loam about 1.4 m deep. The soil is generally rich in lime and slightly alkaline. Table 1 summarises the physical and chemical characteristics of the soil. There is a perched water table at about 1.8 m depth occasionally rising to 1.3 m in parts of the block. Subsurface drainage is achieved with tile-drains installed at a depth of 1.3 m in alternate rows. A vertical sheet of black plastic was inserted to the depth of the drain midway between the rows to prevent inter-row movement of both roots and salt in the top 1.3-m profile. The vineyard was planted in spring 1987 with Sultana vines on their own roots or grafted onto one of seven rootstocks. Thus, there were a total of eight rootstocks including those on their own roots. The vines were spaced at 3.3 m inter-row and 2.5 m intra-row, and arranged in single-row plots of ten vines including a guard vine at each end. There were 24 plots in total and these were arranged in six rows of four plots oriented in a NW-SE direction. The six treatment rows were bordered by a row of wine grapes on either side. Irrigation lines were installed approximately 0.3 m above the soil surface with the drippers spaced 0.8 m apart and set to supply water at a rate of 4 l h–1. Vines were trained on a standard T-trellis with a single foliage wire. Two cane wires were located at 1.2 m height and 0.3 m apart; the foliage wire was 0.3 m above the cane wires. The vines were cane pruned to a maximum of 12 canes each, if available, in July 1994. The vineyard was not cultivated, but was kept largely weed free with the use of herbicides throughout the study period. The first irrigation was applied just before bud break, on account of the dry winter, and water was applied on alternate days to ensure that the water potential at a depth of 0.3 – 0.9 m, as assessed with tensiometers installed at 0.3, 0.6 and 0.9 m depth along the drip line, was kept above –30 kPa, i. e. the soil water content was always close to the field capacity. Treatments

Materials and methods
Site This study was undertaken during the 1994/1995 growing season (September – May) in the Mallee district of north-west Victoria, Australia. The vineyard was located at the CSIRO Division of Horticulture Research Station at Merbein (34°13′S, 142°2′E; 56 m altitude).

The trial was laid out in a spit-plot design with three salinity treatments (described below) which were assigned to the plots arranged in a randomised block design and replicated eight times. Salinity treatments commenced in December 1989. The salinity of the irrigation water was adjusted at three levels of electrical conductivity (EC) by adding sodium chloride (NaCl) to water from the River Murray. The EC for the river water during the season averaged 0.36 dS m–1. Soluble nutrients, principally calcium nitrate

79 [Ca(NO3)2] and potassium nitrate (KNO3), were also added to the irrigation water which increased the salinity by 0.07 dS m–1 for all the salinity levels. Small amounts of calcium chloride (CaCl2) and magnesium chloride (MgCl2) were also added to maintain the sodium adsorption ratio (SAR) of the irrigation water below 15. Thus, mean salinity levels for the 1994/1995 season, including added nutrients and salts, were 0.43 (low), 1.8 (medium), and 3.6 dS m–1 (high). For the current study, there were two sub-treatments consisting of Sultana vines on their own roots (Own-rooted) or grafted onto Ramsey rootstocks (Grafted) and three replicates at each salinity level. Thus the treatments consisted of two vine types by three salinity levels in three replications, i. e. a total of 18 vines were studied. Measurements Canopy development The green area index (GAI), the ratio of total green surfaces (leaves, shoots and fruit when present) to the unit of land area allocated to each vine (8.25 m2), was measured regularly with a Plant Canopy Analyser (LAI-2000, LI-COR, Lincoln, Nebr., USA) following the procedure describe by Sommer and Lang (1994). The analyser was calibrated by destructively sampling shoots for leaf area determination. The fraction of photosynthetically active radiation (PAR) (400 – 700 nm) intercepted by the canopy was monitored with a ceptometer (AccuPAR, Decagon Devices, USA). Readings of incident PAR were taken above and below the canopy on clear days between 11:30 and 12:30 hours EST. Three ‘above-canopy’ readings were obtained for each vine while standing in the open inter-row space, making sure that the senor was fully exposed to direct solar radiation. Two sets of ‘below-canopy’ readings were taken beneath the canopy at ground level, each at a distance of 0.45 m on either side of the vine trunk along the row. Each set of measurements consisted of four readings taken at consecutive positions at right angles to the row direction, running from row centre to row centre. The fraction of PAR intercepted (i) was calculated from the means of the ‘above’ (Io) and ‘below’ (Ib) canopy readings: i = 1–(Ib/Io) (2) Both GAI and PAR measurements commenced 6 weeks after bud burst, which was on 2 September 1994, and continued at 14-day intervals until just before senescence in the second week of May. The light extinction coefficient (K) was obtained from: Ib = Io (e–KGAI) Transpiration Transpiration was determined only in vines under low and high salinity treatments from measurements of sap flux using the heat pulse technique described by Hatton and colleagues (Hatton and Vertessy 1990; Hatton et al. 1990, 1995). For this study, we used commercially available sap flow sensor units (Greenspan Technology, Warwick, Australia); each unit consisted of two probe sets and a data logger. Each probe set contained a heater and a pair of sensors. Both probe sets were installed into the vine trunk separated by a distance of a least 0.4 m and at least 0.30 m from the soil surface. During installation, holes approximately 2.0 mm in diameter were drilled using a 2.2-mm drill bit at right angles into the side of the trunk to a depth of 15 mm, and both the sensors and the heater were implanted. Silicon gel was liberally applied around the points of insertion to seal the wound and keep both the sensors and the heaters firmly in place. The probes and the part of the trunk into which they were installed were wrapped with aluminium foil to minimise the effects of sunlight. Sap flux readings were logged continuously throughout the season at 30-min intervals, and the data were downloaded every week and processed using the software (SAPCAL) provided by the manufacturers. The sap flow sensors were calibrated gravimetrically by weighing potted vines, which had sap flow sensors installed, over an 8-day period. The relationship between the sap flow sensors (y) and (3) the gravimetric method (x) in their estimation of accumulative daily T was: y = 1.057x r2 = 0.987, n = 8 (4) From the sap flux data, daily rates of sap flow per vine were calculated, which were then scaled to unit land area to estimate vine transpiration using the tessellation method (Hatton and Vertessey 1990). Sap flux measurement was made throughout the season beginning soon after bud burst until leaf senescence in May. Stomatal resistance and leaf temperature Three shoots which were fully exposed to direct solar radiation were marked during the fourth week after bud break. Stomatal resistance (rs) was measured with a porometer (AP4 Porometer, Delta-T Devices, Cambridge, UK) on three leaves from each shoot. These measurements were made between 10:30 and 13:30 hours EST starting at 72 days after bud burst (DAB), and repeated at approximately 14-day intervals until leaf senescence. Leaf temperature was inferred from the temperature difference between the porometer cup and the leaf. Canopy resistance (Rc) was calculated as: rs/GAI (Monteith and Unsworth 1990). Soil evaporation This was estimated using the two-stage evaporation model of Ritchie (1972) by which evaporation rates are based on evaporative demand during the first stage (Es1), immediately following recharge of the soil profile by rain or irrigation, and on soil hydraulic characteristics during the second stage (Es2), once the soil surface dries out: ∑ Es1 =[?/(? + γ)] Rn [exp (– K GAI)] ∑ Es2 = Ct
0.5

when ∑ Es < U when ∑ Es < U

(5) (6)

where ? is the slope relating saturation vapour pressure to temperature, γ is the psychrometer constant, Rn is net radiation and the term exp(–KGAI) is the fraction of radiation transmitted through the canopy to the soil surface; both U and C are soil parameters denoting the theoretical maximum amount of soil water that can be lost during Es1 and the soil hydraulic characteristic, respectively. A U value of 7.1 mm and a C of 5.0 mm1/2 were determined during the high Epot conditions in summer, as suggested by Yunusa et al. (1994), with microlysimeters. During rainy periods, Es was calculated with Eq. 5 for the whole plot. However, during dry periods, the plot was zoned into two. Zone 1 consisted of a 1-m band centred along the drip line, which was moist throughout the season as a result of frequent irrigation, and therefore considered to be perpetually in the first stage; Es from this zone was calculated with Eq. 5 but using the fraction of radiation transmitted to this band measured directly with the ceptometer. Zone 2 consisted of the remaining part of the plot, where the soil surface was mostly dry, and Es was calculated with Eq. 6. Hence, during dry periods, Es for the whole plot was obtained by integrating values from the two zones after multiplying each by the respective fractions of plot surface area accounted for by the zone, i. e. 0.303 for zone 1 and 0.697 for zone 2. Crop water use, i. e. evapotranspiration (ET), was obtained as the sum of T and Es. Soil water Storage of soil water (S) was monitored with a neutron probe (CPN, USA). Three aluminium access tubes were installed per vine: two were under the drip line at 0.45 and 0.90 m from the vine trunk, and one was placed in the inter-row space at 0.45 m from the vine and oriented at right angles to the row. Neutron probe readings were taken at 0.1-m increments between 0.2 and 0.6 m depth, and thereafter at 0.2-m increments to 1.2 m depth. These measurements started a week after bud burst and were repeated at 14-day intervals until the end of the season.

80 Yields and water use efficiency The fruit was harvested on 16 February 1995, i. e. at 167 DAB. Fruit from each vine was weighed fresh soon after picking, and the yield expressed per unit land area for the calculation of CWUE. CWUE was expressed in terms of either fruit yield per unit of total T at harvest (CWUEt) or fruit yield per unit of total ET at harvest (CWUEET). Weather Key weather variables – minimim and maximum temperatures, solar radiation, humidity, wind run and rainfall – were monitored with an automatic weather station. Potential evaporation (Epot) was determined with a modified Penman equation as given by Meyer (1993). Additional crop and water use data from the 1993/1994 season Transpiration was monitored between January and March 1994 in the same vines used in 1994/1995 season following the procedure described above. In addition, GAI was measured with LAI-2000 in mid-February. At harvest, the fresh weights of fruit for each of the 18 vines were determined. In this season, but burst was completed by 20 September 1993, and harvesting was carried out on 3 March 1994. The salinity levels for the three treatments in 1993/1994 were similar to those in the following season. Statistical analysis All the plant and soil data were analysed according to a split-plot design (Mead and Curnow 1983) using the SYSTAT statistical package (SYSTAT, Evanston, Ill., USA).

Fig. 1 a – c Weekly averages of mean daily weather variables at Merbein during the 1994/1995 growing season. a Temperatures. b Vapour pressure deficit (VPD) and Wind speed. c Potential evaporation (Epot) and major rainfall events

Results

Weather The temperature profile during the 1994/1995 season (Fig. 1 a) was consistent with a cool spring and autumn and a hot summer, as normally experienced in the region. The vapour pressure deficit increased from around 0.7 kPa in September to maxima of around 2.5 kPa in December/January before falling to less than 0.5 kPa at the end of the season in May (Fig. 1 b). Wind speed (Fig. 1 b) was more than 3.0 m s–1 during the summer period (December – February), and fell below 2 m s–1 only after March. Hence, Epot (Fig. 1 c) rose from around 4 mm day–1 in September (spring) to maxima of more than 7 mm day–1 in late November – February (summer); Epot totalled 1500 mm for the study period between 1 September 1994 and 16 May 1995. Rainfall (Fig. 1 c) was rare and mostly occurred as light drizzle, exceeding 10 mm on only five occasions. Rootstock effects on canopy and ET characteristics Except for a 60-day period at the beginning of the season, Grafted produced significantly greater GAI and i than Own-rooted throughout the season. Between 60 and 109 DAB, the rate of GAI development (Fig. 2 a) averaged 0.033 day–1 (or 0.273 m2 of green area day–1) for Grafted compared to 0.019 day–1 (0.158 m2 day–1) for Own-rooted.

Fig. 2 a, b Effects of rootstock on green area index (GAI) (a) and fraction of photosynthetically active radiation (PAR) intercepted (i) by grapevines (b) at Merbein during the 1994/1995 season. For each data point, n = 9; the bars are standard errors of the difference. The arrow head indicates the time of harvest

Likewise, i (Fig. 2 b) for Grafted increased at almost twice the rate for Own-rooted during the same period. Regression parameters used for determining K were similar for both rootstocks; the intercepts were –0.046±0.051 for Own-rooted and –0.059±0.056 for

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Fig. 3 Regression of the natural logarithm of the fraction of PAR transmitted through the canopy (1–i) on GAI for grapevines at Merbein during the 1994/1995 growing season. The slope of the regression line was taken as the extinction coefficient (K): –ln (1–i) = –0.025 –0.182 GAI, r2 = 0.871, n = 22. Both GAI and i data were taken from Fig. 2

Fig. 5 Relationship between daily rates of transpiration (T) and canopy resistance (Rc) for grapevines during the summer (December – mid-March). Each data point is a mean of six vines from low and high salinity treatments. The regression equation is: T = 1.83*Rc–0.183

Fig. 4 a, b Effects of rootstock on weekly averages of daily rates of transpiration (T) (a) and soil evaporation (Es) (b) for grapevines at Merbein during the 1994/1995 growing season. For T data, n = 9; the arrow head indicates time of harvest

Grafted, while the slopes (K) were –0.155±0.063 and –0.177±0.033, respectively. Since the regression parameters for the two rootstocks were within one standard error of each other, the two sets of data were pooled (Fig. 3) to determine a common K of 0.182 for both types of vine. Rates of T (Fig. 4 a) during the first 80 days (September – November) were similar for Own-rooted and Grafted. However, between 90 and 180 DAB (December – February), i. e. in the summer season, the rates of T averaged about 30% higher for Grafted than for Own-rooted: 0.9 mm day–1 (or 7.5 l per vine) compared to 1.2 mm day–1 (9.9 l).

During most of this period, rates of T changed very little for both rootstocks. Shortly after 180 DAB, rates of T fell rapidly until the end of the season; the decline in rates was more rapid for Own-rooted than for Grafted. To calculate Es, the K based on PAR was adjusted for net radiation (300 – 3000 nm) by multiplying it by 0.78, which was the ratio of K based on net radiation to that based on PAR calculated from the published data of Szeicz (1974). Es (Fig. 4 b) was similar for Own-rooted and Grafted in the first 90 DAB with a mean rate of 1.0 mm day–1. After this period, Es was consistently higher for Own-rooted than for Grafted until the end of the season, coinciding with maximum differences in canopy size between the two types of vines. In summer, rates of Es were close to T rates for Own-rooted, but were about half the T rates for Grafted (Fig. 4). Total Es during the season was 237 mm for Own-rooted and 187 mm for Grafted. Between November and March, an inverse relationship was found between T and Rc (Fig. 5). T decreased curvilinearly with increases in Rc, and the curve tended towards asymptote. The leaf-air temperature difference (data not presented) was similar for Own-rooted and Grafted, but it increased from less than 2 °C in late October to more than 4 °C by harvest. ET rates obtained as the sum of T and Es were similar for both Own-rooted and Grafted throughout the season, so only the mean values are presented in Fig. 6 a. Rates of ET increased rapidly after 30 DAB reaching maxima of more than 2.0 mm day–1 in summer, before declining rapidly after 180 DAB due to the onset of low temperatures and, later, leaf senescence. Rates of water applications during the season (Fig. 6 a) increased from a low of 0.94 mm day–1 in the first 30 days to a high of 2.61 mm day–1 between 90 and 210 DAB. Thus, rates of irrigation were as much as 60% greater than those of ET in the summer (Fig. 6 a). At the end of the season, total irrigation of 481 mm was 26% higher than the mean total ET of 382 mm. The mean Kc for Own-rooted and Grafted (Fig. 6 b) was generally below 0.30, except during the occasional periods of rainfall, and averaged 0.25 during the study period.

82 Table 2 Effects of salinity on the mean green area index (GAI), fraction of photosynthetically active radiation intercepted (i) and total transpiration (T) for Sultana vines at Merbein in January and March 1995 (n = 6). n. a. Data not available Salinity January Low Medium High SE March Low Medium High SE GAI i Total T month–1 (mm) 31.5 n. a. 28.2 2.88 27.5 n. a. 19.1 4.78

2.98 2.68 2.38 0.292 2.09 2.04 1.25 0.203

0.37 0.37 0.32 0.025 0.34 0.33 0.25 0.015

Fig. 6 a – c Components of soil water balance: weekly averages of daily rates of irrigation and mean evapotranspiration (ET) for Own-rooted and Grafted (a); weekly averages of crop factors based on mean ET (Kc) for both vine types, or T (Kt) for Grafted (b); water stored (S) in the 1.2-m soil profile during the 1944/1995 growing season at Merbein, with the bars indicating the SEM and the arrow head, the time of harvest (c). For ET and Kc, n = 12; Kt, n = 6; S, n = 48

of around 0.35. The outliers in Fig. 7 occurred during the last 6 weeks of the season, which experienced progressive falls in temperatures and Epot. Total storage of water in the soil profile did not change significantly during the growing season, and the increases in S observed at the end of the season (Fig. 6 c) were within 1 SE of the mean storage at bud burst. Salinity effects on canopy and ET characteristics No significant effects of salinity were observed on the measured plant variables for most of the season in 1994/1995. The trends in GAI, i and rates of T during the pre-harvest period were typified by their mean values for the month of January (Table 2). Although these variables were lowest for high salinity, differencs between treatments were not significant. However, the decrease in these variables from about 4 weeks after harvest was more rapid for high salinity than for low and medium salinity. Hence, by March, high salinity significantly reduced both GAI and i, and also T, by almost 31% (Table 2). Both Es and ET were similar for the two salinity levels during both January and March (data not presented). Components of the soil water balance Changes in components of the soil water balance during the entire season are summarised in Table 3. There were no significant effects of salinity on any of the variables quantified. Grafted significantly increased mean T by 31.9% compared to Own-rooted. The interaction between rootstock and salinity on T was significant: Grafted at low salinity had the highest seasonal T, which was 34% more than T for Own-rooted at high salinity. Es totalled 237 mm for Own-rooted and 187 mm for Grafted, accounting for 62 and 49% of the seasonal ET, respectively. The difference between the seasonal totals of ET and irrigation constituted D, which averaged 99 mm for all treatment. Thus, IWUE averaged 0.80 (Table 3).

Fig. 7 a, b Relationships between crop factors based on transpiration (Kt) and GAI (a) and fraction of PAR intercepted (i) (b) during the growing season. The open symbols are outliers. Each data point is a mean of six vines from low and high salinity treatments. The equations for the fitted lines are: (a) Kt = 0.156/[1+exp(1.949 –1.89* GAI)]; (b) Kt = 0.156/[1+exp(2.24 –17.811*i)]

Kt is presented for Grafted only (Fig. 6 b) due to small numerical differences between Own-rooted and Grafted. Kt averaged 0.12 for Grafted and 0.10 for Own-rooted during the season. There were strong sigmoidal relationships between Kt and both GAI (Fig. 7 a) and i (Fig. 7 b). Kt-canopy cover relationships were asymptotic at a Kt value of 0.15, which was attained at a GAI of around 3.0 and an i

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Fruit yield and CWUE Since this paper is not designed to analyse yield responses in detail, only the data for the three replicates measured are presented (Table 4). Briefly, the fresh fruit yield averaged 7.1 kg per vine for Own-rooted compared to 19.0 kg for Grafted. While the yield for Grafted was unaffected by
Table 3 Effects of rootstock and salinity of irrigation water on seasonal transpiration (T), evapotranspiration (ET), estimated drainage and irrigation water use efficiency (IWUE) for Sultana grapevines during the 1994/1995 growing season at Merbein. Soil evaporation averaged 237 mm for Own-rooted and 187 mm for Grafted; irrigation totalled 481 mm. Statistical analysis for T only. P is the probability of the F ratios of the analysis of variance being significant; SE is the standard error of the difference between means Salinity Rootstock Own-rooted T (mm) Low High Mean (n = 6) ET (mm) Low High Mean (n = 6) Drainage (mm) Low High Mean (n = 6) IWUE Low High Mean (n = 6) P Salinity Rootstock Salinity × rootstock 0.248 0.022 0.038 148.1 145.3 146.7 385.0 382.3 383.7 97.0 99.7 98.3 0.80 0.79 0.80 Grafted 195.3 191.7 193.5 382.1 378.7 380.4 99.9 103.3 101.6 0.79 0.79 0.79 SE 21.45 10.67 15.09 Mean (n = 6) 171.7 168.5

salinity, that for Own-rooted was more than halved by both medium and high salinity treatments. Mean CWUEt (Table 4) was reduced by 29% with high salinity, although the effect was not significant due to the large variability in the data; mean CWUEt for Grafted was 44% more than for Own-rooted. While at low salinity, CWUEt was similar for both rootstocks, at high salinity, it was more than halved for Own-rooted. The response of CWUEET (Table 4) to treatments was similar to that of CWUEt, although Grafted produced more yield per unit of ET than Own-rooted at both salinity levels. CWUEET values were generally about half CWUEt. Supplementary results from the 1993/1994 season Fruit yield at low salinity (Table 5) was 29% lower for Own-rooted than for Grafted. Yield at high salinity was reduced by 21% for Own-rooted but increased by 18% for Grafted. GAI was unaffected by salinity, but grafted vines produced 25% more GAI than Own-rooted in March 1994 (Table 5). T rates (Table 6) did not exceed 1.0 mm day–1 for either vine type during the late summer period. While T rates were 20% higher for Grafted than for Own-rooted in January, the difference fell to less than 15% in March. Kt averaged 0.12 for Grafted compared to 0.10 for Ownrooted during this late summer to early autumn period (Table 6). Since the Kt values (Table 6) were close to those observed for a similar period in the 1994/1995 season (see Fig. 6 b), we assumed that the average Kt for the whole preharvest period night be similar for the two seasons. Therefore, T during the pre-harvest period for the 1993/1994 season was approximated as the product of cumulative Epot from bud burst to harvest in that season and mean Kt for the same period in 1994/1995; this yielded T of 98 mm for Own-rooted and 126 mm for Grafted in the 1993/1994 season (Table 6). CWUEt was only 11% higher for Grafted compared to Own-rooted (Table 6). Both the yields and
ing the 1994/1995 season at Merbein. n. a. Data not available, P probabilities of the F ratios in the analysis of variance being significant, SE standard error of the difference between means CWUEt a (kg ha–1 mm–1) CWUEETb (kg ha–1 mm–1) Ownrooted 59.6 n. a. 25.8 42.7 P 0.057 0.005 0.017 Grafted 90.2 n. a. 82.6 86.4 SE 20.70 15.44 18.48 Mean (n = 6) 74.9 n. a. 54.2

383.6 380.5

98.4 101.5

0.80 0.79

Table 4 Effects of salinity and rootstock on the fruit yield, and crop water use efficiency based on transpiration (CWUEt) and evapotranspiration (CWUEET) for the fruit yields for Sultana grapevines durSalinity Yield (kg per vine) Ownrooted Low Medium High Mean (n = 9) 11.1 5.3 4.9 7.1 P Salinity Rootstock Salinity × rootstock
a b

Grafted 16.3 23.8 16.8 19.0 SE 1.07 1.22 2.88

Mean (n = 6) 13.8 14.5 10.9

Ownrooted 161.7 n. a. 67.4 114.6 P 0.057 0.049 0.006

Grafted 165.9 n. a. 164.2 165.0 SE 33.93 12.77 46.24

Mean (n = 6) 163.8 n. a. 115.8

0.047 0.000 0.006

Based on total transpiration at time of harvest Based on total evapotranspiration at time of harvest

84 Table 5 Effects of salinity and rootstock on fresh fruit yields at harvest and GAI in March for Sultana grapevines during the 1993/1994 growing season at Merbein. P, probability of F ratio in the analysis of variance being significant, SE standard error of the difference between means Salinity Yield (kg per vine) Ownrooted Low Medium High Mean (n = 9) 21.8 23.5 17.2 20.8 P Salinity Rootstock Salinity × rootstock 0.035 0.001 0.039 Grafted 30.9 49.4 36.6 39.0 SE 3.74 3.41 5.91 Mean (n = 6) 26.3 36.5 26.8 GAI (March) Ownrooted 1.71 1.82 1.56 1.70 P 0.895 0.046 0.424 Grafted 2.22 1.88 2.28 2.13 SE 0.251 0.140 0.242 Mean (n = 6) 1.96 1.85 1.92

Table 6 Water use variables for Sultana grapevines irrigated with water of low salinity during the 1993/1994 growing season. Mean daily transpiration (T), estimated total transpiration for the pre-harvest period and crop water use efficiency based on transpiration Rootstock T (mm day–1) Jan Own-rooted Grafted 0.77 (0.10) 0.93 (0.11) Feb 0.62 (0.10) 0.70 (0.12)

(CWUEt) (n = 3). Values in parentheses are the crop coefficient based on transpiration (Kt = T/Epot; see Introduction). Mean daily rates of Epot were January 8.5 mm, February 6.1 mm, March 5.7 mm Pre-harvest T (mm) 98 126 CWUEt (kg ha–1 mm–1) 266.3 294.4

Mar 0.61 (0.11) 0.70 (0.12)

CWUEt were at least 1.5-fold those observed in the 1994/1994 season (see Table 4).

Discussion

Water use and crop factors Grapevines appear to be conservative in their water use. The maximum T of 1.2 mm day–1 (Fig. 4), attained when the canopy size was at its peak in the summer, was a small fraction of Epot (ca. 8.0 mm day–1) as indicated by the Kt data (Fig. 6 b). This resulted largely from the low fraction of radiant energy intercepted by the vine canopy. The concentration of foliage elements around the trellises caused clumping and mutual shading of leaves, and allowed much of the incident radiation to be transmitted to the soil surface between the vine rows. Hence, despite the large GAI (Fig. 2 a), K was low (Fig. 3) because i rarely exceeded 0.45 (Fig. 2 a). This was in contrast to field crops such as wheat, in which a GAI of 2 may produce i of up to 0.6 and K of at least 0.35 (Yunusa et al. 1993). In addition to the low energy intercepted, the strong inverse relationship between T and Rc in the summer (Fig. 5) suggested that T was also restrained by stomatal control. This may explain the lack of response in T to the transient peaks in Epot during the summer. Grapevines are known to close their somata even when well supplied with water under high Epot conditions as a result of low humidity (Lange and Meyer 1979) or high VPD (Loveys 1984). Hence, Kt

(Fig. 6 b) was consistently less than i (Fig. 2 b), indicating that not all of the energy intercepted was used for transpiration resulting in the leaves being warmer than the air in the summer (data not presented), i. e. the canopy became a significant energy sink during the day (Jones 1983). Rates of T found in this study (Fig. 4) were similar to those observed in vineyards in the northern hemisphere. Measurements of sap flow in irrigated vines in North America, produced T of between 0.8 and 1.6 mm day–1 in a vineyard with 1960 vines ha–1 at Lamese (33.5 °N, 102 °W) (Heilman et al. 1994), and of 1.24 mm day–1 in a vineyard with 2600 3-year-old vines ha–1 at New Deal (33°45′N, 101°50′W) (Lascano et al. 1992). In a rain-fed vineyard at Tomelloso, Spain (39°10′N, 3°1′W), Oliver and Sene (1992), using an energy balance approach, calculated an average T of 1.0 mm day–1 for grapevines which, at midday, intercepted up to 60% of the incoming solar radiation. ET obtained by summing T and Es (Fig. 6 a) was similar to that calculated using the soil water balance method, in the absence of drainage, during the first half of the season. ET obtained periodically with these two methods between bud burst and 104 DAB were correlated (r2 = 0.82, data not presented), and totalled 161 and 168 mm for Ownrooted and Grafted, respectively, when based on soil water balance compared to 162 and 165 mm, respectively, from separate estimates of T and Es. This similarity validated Es estimates from the Ritchie model, and determination of ET from estimates of Es and T throughout the season. The accuracy of the soil water balance method in calculating ET was impaired by drainage arising from overirrigation in the second half of the season. Most of the over-

85

irrigation occurred between 90 and 210 DAB (summer, Fig. 6 a), a period of high Epot and canopy cover, and berry filling, phenomena most growers associate with significant increases in crop water requirement, but a view not supported by the stable rates of T during the summer (Fig. 4 a). However, high rates of Es (Fig. 4 b) signify substantial loss of irrigation water along the drip line especially under canopies, such as those of Own-rooted, which shade this zone poorly. The Es/ET ratio averaged 0.55 for both types of vine (Table 3) and was within the range of 0.44 – 0.68 found in a drip-irrigated vineyard (Heilman et al. 1994). Both the seasonal ET (Table 3) and Kc (Fig. 6) are comparable to those obtained for sprinkler-irrigated 12-yearold vines planted at around 2900 vines ha–1 in South Africa (Van Zyl and Van Huyssteen 1980). Van Zyl and Van Huyssteen (1980) also reported that Kc fell below 0.10 during extended dry periods, when Es was minimal, even though more than 50% of the soil surface was shaded by the canopy. However, the ET values found in the present study were lower by at least 45%, and peak Kc by 64%, than those published for vines planted at a similar density in the Mallee district (Prior and Grieve 1986). Prior and Grieve (1986) acknowledged that their high rates of irrigation (>1000 mm per season) were about 18% more than the anticipated crop water requirement. Errors in their estimation of D could possibly account for the high ET (>700 mm per season) reported. Rainfall totalled 167 mm during the current study, but was not considered in the analysis of IWUE because most of it fell as light drizzle with only a few events large enough (Fig. 1 c) to contribute to T. Inclusion of the seasonal rainfall would reduce IWUE by about 20%, but this may be offset by leaching requirement (about 15% of ET). Furthermore, because irrigation was in excess of ET, Gw (Eq. 1) could be negligible and was excluded from calculation of the soil water balance in this study. The equations in Fig. 7 could be used to estimate T on the basis of canopy growth. An allowance can then be made for Es to determine the amount of water to apply. When coupled to models for predicting canopy development, these equations could be used to forecast crop water requirement for any given season. The outliers in Fig. 7 occurred during the cool, terminal 6 weeks of the season when the vines were more able to meet the comparatively low evaporative demands than the high demands of the preceding period, as indicated by the increases in Kt between 200 and 240 DAB (Fig. 6 b). Effects of rootstock and salinity on CWUE Higher yields for Grafted (Table 4) were associated with greater scion vigour on the Ramsey rootstock which ensured greater i (Fig. 2) and T (Table 3) compared to Ownrooted. Differences in CWUE based on either T (CWUEt) or ET (CWUEET) are in accord with the differences in the yields of the two rootstocks (Table 4). There is limited information in the literature on CWUE, however, the CWUEET values for Own-rooted at low salinity of 59.6 kg

ha mm (Table 4) were similar to the 54.5 kg ha mm–1 for drip-irrigated ‘Thompson Seedless’ grapevines calculated from the data of Araujo et al. (1995). The higher salt tolerance of Grafted vines is often associated with the ability of the Ramsey rootstock to exclude salts (Sauer 1968; Downton 1977 b, 1985; Walker 1994). Reasons for the low yields in the 1994/1995 season are not certain, but fruitfulness in vines has been associated in particular with light and temperature conditions during the period of fruit bud initiation in the previous season (May and Antcliff 1963; Baldwin 1964), and with weather conditions in both the previous season and the season of harvest (May and Antcliff 1963). A further discussion of the yield responses in this trial is presented elsewhere (Walker et al. 1996). The lack of significant effects of salinity on canopy growth and T during most of the pre-harvest period (Table 2) was contrary to reports from previous studies (Prior et al. 1992 a, b; R. R. Walker, F. Iacono, D. Blackmore, unpublished data). The differences could be related to site, seasonal or management differences. For example, there was no evidence that Prior et al. (1992 a, b) adjusted the SAR of their irrigation water, which could have risen to higher levels than in our study. Possible differences in the nutritional status of the soils between the two sites could also be involved. For instance, Pandey and Divate (1976) found that bivalent cations, present in considerable amounts at our site (Table 1), reduced the detrimental effects of salinity on vines. Furthermore, Perera et al. (1995) found that increasing the concentration of calcium ions in the rooting medium proportionally reduced the inhibitory effects of salinity on stomatal conductance. Additional data on the effects of salinity on canopy growth, e. g. pruning wood weights, for the current study are given by Walker et al. (1996).

–1

–1

–1

Conclusions

Seasonal water use was similar for Sultana vines growing either on their own roots or grafted onto Ramsey rootstock. However, the two types of vine differed in their partitioning of ET between T and Es due to differences in their vigour. The Ramsey rootstock enhanced canopy development which promoted T while reducing Es, whereas the smaller canopies of the own-rooted vines transpired less water and exposed more of the soil surface to evaporation. The relatively high rates of Es under both types of vine showed how significant proportions of irrigation water are lost under high-frequency irrigation systems even though only small fractions of the soil surface are wetted. Furthermore, the grapevines appeared to be conservative in their water use as a result of the generally low rates of T which were associated with low levels of energy interception, and stomatal control. An IWUE of 0.80 indicates there is still some room for improvement by adopting approaches that match water applications more closely to crop requirements. In arid and semi-arid environments, where canopy cover is mostly incomplete, the use of Kt to determine water re-

86

quirements would be more appropriate than using Kc alone, especially with irrigation systems that wet only small fractions of the soil surface.
Acknowledgements We thank Jenny Guy and Mark Symes for their technical support, Ian Lauder for preparation of access tubes, and Dr. Karl J. Sommer for setting up the leaf area meter. The neutron probe was loaned from the Soil and Water Management Group at the Sunraysia Horticultural Centre, and we thank Mark Dale, Paul Burrows and Paul McClure for their cooperation. We also thank Peter Clingeleffer for facilitating yield measurements. The study was partly funded by the Murray Darling Basin Commission through the Natural Resources Management Strategy scheme, and the Dried Fruit Research and Development Council.

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xylem-derived abscisic acid on leaf gas exchange. New Phytol 98: 563 – 573 May P, Antcliff AJ (1963) The effect of shading on fruitfulness and yield in the Sultana. J Hort Sci 38: 85 – 94 Mead R, Curnow RN (1983) Statistical methods in agriculture and experimental biology. Chapman & Hall, London Meyer WS (1993) Standard reference evaporation calculated for inland south eastern Australia. Tech Memo, CSIRO Inst Nat Resour Environ, Div Water Resour, Griffith Monteith JL, Unsworth MH (1990) Principles of environmental physics. Arnold, London Nagarajah S (1987) Effect of soil texture on the rooting patterns of Thompson seedless vines on own roots and Ramsey rootstock in irrigated vineyards. Am J Enol Vitic 38: 54 – 59 Oliver HR, Sene KJ (1992) Energy and water balances for developing vines. Agric For Meteorol 61: 167 – 185 Pandey RM, Divate MR (1976) Salt tolerance in grapes. I. Effects of sodium salts singly and in combination on some of the morphological characters of grape varieties. Ind J Plant Physiol 19: 230 – 239 Penman F, Taylor JK, Hooper PD, Marshall TJ (1939) A soil survey of the Merbein irrigation district, Victoria. Bulletin no 123. Council of Scientific and Industrial Reserach, Melbourne, Australia Perera LKRR, Robinson MF, Mansfield TA (1995) Response of stomata of Aster tripolium to calcium and sodium in relation to salinity tolerance. J Exp Bot 46: 623 – 629 Prior LD, Grieve AM (1986) Water use and irrigation requirements of grapevines. Proc 6th Aust Wine Tech Conf. July 14 – 17, Adelaide, pp 165 – 168, Adelaide: Australian Industrial Publishers Prior LD, Grieve AM, Cullis BR (1992 a) Sodium chloride and soil texture interactions in irrigated field grown Sultana grapevines. I. Yield and fruit quality. Aust J Agric Res 43: 1051 – 1066 Prior LD, Grieve AM, Cullis BR (1992 b) Sodium chloride and soil texture interactions in irrigated field grown Sultana grapevines. II. Plant mineral content, growth and physiology. Aust J Agric Res 43: 1067 – 1083 Ritchie JT (1972) Model for predicting evaporation from a row crop with incomplete cover. Water Resour Res 8: 1204 – 1213 Sauer MR (1968) Effects of vine rootstocks on chloride concentration in Sultana scions. Vitis 7: 223 – 226 Sommer KJ, Lang ARG (1994) Comparative analysis of two indirect methods of measuring leaf area index as applied to minimal and spur pruned grape vines. Aust J Plant Physiol 21: 197 – 206 Szeicz G (1974) Solar radiation in crop canopies. J Appl Ecol 11: 1117 – 1156 Van Zyl JL, Van Huyssteen L (1980) Comparative studies on wine grapes on different trellising system: I. Consumptive water use. S Afr J Encol Vitic 1: 1 – 14 Walker RR (1994) Grapevine response to salinity. Bull OIV 67: 634 – 661 Walker RR, Torokfalvy E, Scott NS, Kriedmann PE (1981) An analysis of photosynthetic response to salt treatment in Vitis vinifera. Aust J Plant Physiol 8: 359 – 374 Walker RR, Blackmore DH, Clingeleffer PE (1996) Salinity-vine vigour interactions and their effects on fruitfulness and yield of Sultana on Ramsey rootstock and on their own roots. Dried Fruit News NS 23: 16 – 18 Williams LE, Williams DW, Phene CJ (1992) Modelling grapevine water use. Proc 8th Aust Wine Ind Tech Conf, 25 – 29 October, Melbourne, pp 29 – 33, Adelaide Winetitles Yunusa IAM, Siddique KHM, Belford RK, Karimi MM (1993) Effect of canopy structure on efficiency of radiation interception and use in spring wheat cultivars during the pre-anthesis period in Mediterranean-type environment. Field Crops Res 35: 113 – 122 Yunusa IAM, Sedgley RH, Tennant D (1994) Evaporation from bare soil in south-western Australia: a test of two models using lysimetry. Aust J Soil Res 32: 437 – 446


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