Plate 24.Grafted vines in the nursery, after incubation at 28°C. The buds start to push and shoots form during this time, adding a bit of colour to the nursery.
Plate 25.Use of plastic mulch during vineyard establishment, which conserves moisture and reduces weed competition. Disposal of the plastic once it starts to degrade is a problem, however.
Plate 26.Montage of different types of vine shelters.
Plate section supported by John Coleman of Plasma Physics Corporation.
25
Plate 27.A trellis-less vine in Greece. Vines are woven into a basket shape to encourage collection of early morning dew, and spaced far apart to so the amount of soil water available to the vine is maximized (Photograph reproduced with permission, L. Brenner).
Plate 28.Vines trained to an Umbrella Kniffen-style system in Margaret River area of Western Australia. The canes are arched over wires placed at the desired height over the vine heads.
Plate 29.Sylvoz trained vines, where their short canes are tied to a lower wire.
29
28
Plate 30.An overhead vineyard trellis system growing Sultana grapes for fresh consumption in Chile.
Note the fresh shoots on the ground, which are the result of shoot thinning to open up the canopy.
Plate 31.Mussel shells as part of a research trial at Neudorf Vineyards in Nelson, New Zealand.
Plate 32.Shoots that have been damaged in a radiation frost. Only the tips have been affected as heat loss from these was greater than the leaves below, which were protected from direct radiation loss by the shoot tips.
31
32
Plate 33.A row of fuel burners in a Californian vineyard. Though common in years past, they are becoming less used due to cost, convenience and environmental concerns.
Plate 34.The aftermath of frost protection using sprinklers. Inside the ice the vine tissues are still unfrozen (Photographs courtesy, D. Darlow).
Plate 35.Micro-sprinklers mounted atop each vineyard post deliver water evenly over the vineyard.
Plate 36.Leaf and shoot removal in a VSP vineyard. Management of these vines is to remove all of the leaves in the fruiting zone.
Plate 37.Berries that have been damaged from late season leaf removal. Direct exposure to the sun and heat has caused blackening of the berries.
36
Plate 38.The interior of a dense and wide canopy. Note that the shoot carrying the lower cluster has lost all its leaves due to the lack of light.
Plate 39.An example of severe chlorine toxicity in an Australian vineyard. The marginal chlorosis is not diagnostic of this however, as these symptoms can appear through a number of different ways.
Plate 40.A broken end assembly post caused by passing machinery, because the post was slightly out of line with the row.
40
Plate 41.Botrytis infection contributing to ‘noble rot’ of some Riesling grapes. Note the shrivelled but whole berries.
Plate 42.Botrytis has infected frost damaged shoot tissue, creating a source of inoculum for later in the season.
Plate 43.Point infections of Botrytis on Sauvignon blanc berries. It is likely that the entry point was a defect or a stomatal pore in the berry skin.
43
Plate 44.Powdery Mildew on left, grapevine leaves, showing leaf curling; right, shoots, and lower, overwintering canes (dark areas).
Fig. 6.39. Flood irrigation in a New South Wales, Australia ‘Semillon’ vineyard.
The land must be levelled quite precisely for flood irrigation to be efficient.
Fig. 6.40. A modification of flood irrigation: twin-furrow. This system uses less water than the basic one, but has similar drawbacks.
Targeted irrigation, usually using a series of pipes and tubes to deliver water to the vines, is now common in many viticultural regions. Establishment costs can be high, but there are savings in the amount of water used and advantages with the precision to which water can be applied to vines.
Typically, a small tube is laid down under each row and drippers (also called emitters) ⫺either built in or inserted at appropriate intervals ⫺deliver water at a known rate. Tubes can be tied to a wire or simply rest on the ground (see Fig. 6.41). Older-style emitters often required the former method, as soil particles could be sucked back up into the tube as it drained, but the modern irrigation laterals are quite robust and simply need to be kept away from machinery paths.
In areas with high temperatures and low water availability, irrigation tubes can be buried underground, delivering the water directly to the root zone and further increasing the efficiency of application (Camp, 1998).
Fig. 6.41. Irrigation lateral tube with built-in emitters. The short distance between emitters ensures an evenly irrigated line down each row, which is especially advantageous with newly planted vines.
Methods of monitoring soil moisture
In grape-growing areas that need supplementation of water supply, investment in some means of measuring soil water will benefit management of the vineyard. Observing the trends of how the soil profile dries out allows advance planning as to when to schedule irrigation, which can save on water and pumping costs and maintain vine growth at a preferred rate. Addition of too much water simply multiplies the work necessary to keep the canopies in good shape: more shoot trimming and leaf removal at the very least.
At its most simple, the amount of moisture in the soil can be followed through simple calculations of data available in many weather reports. If the soil starts the season at field capacity (where no more water can be held by the soil), evaporation pan data (a standardized method of measuring water loss from liquid form into the atmosphere) can be converted to evapotranspiration that occurs from plants. The formula for this is
evapotranspiration (ET) = evaporation pan figure (Epan)⫻crop factor (kc) The crop factor adjustment accounts for the difference between water loss from an open pan of water and water loss from plant stomata, with values typically ranging from 0.2 to 0.5 (Nicholas, 2004). The crop factor will vary between plant types, and also with the stage of development of the plants, as small grapevine shoots early in the season transpire less water than a full canopy later on. However, if a cover crop is present, the overall crop factor may not change much over a growing season (Yunusa et al., 1997).
The water lost to evapotranspiration can be calculated on a daily or monthly basis (at whatever frequency that Epandata are available) and subtracted from the field capacity value, which has added to it any rainfall and/or irrigation applied.
Figure 6.42 shows an example of a season’s soil moisture as estimated through these types of calculations. In this example, irrigation needed to be applied to keep the plant-available water from dropping below zero. Even though there is quite a bit of rainfall in the winter and spring, none of this is usable in the soil profile because it is already at field capacity. Note that there is still a deficit in soil moisture at the end of the season that may not be replenished by winter rainfall: if this was the case, additional irrigation would be required in the following season.
As an indirect method of keeping track of soil moisture this has its advantages, as no equipment is needed; however, your particular site may not have the same weather conditions as the site from which the data come, which can lead to significant errors in determining the amount of water left for the vines. Unless this method is combined with periodic verification with some form of direct soil water measurement, it can only be used as an indication of irrigation needs. More precise management techniques will require other methods.
The amount of water in the soil can be measured, or the water status of the plant can be estimated. Quantifying the former can be done through measuring soil moisture tension, which is the amount of force required to extract water
from the soil particles (this is the same force that a plant root has to contend with). A tensiometer (a partly filled water tube with a porous cap on the bottom and a vacuum gauge on the top) measures this directly when it is buried to the appropriate depth in the soil. As the soil dries out, water moves from the porous cap into the soil, creating a vacuum in the tube, which registers on the gauge.
These are fairly simple devices that work well at higher soil moisture contents (Tollner and Moss, 1988). However, because grapevines are fairly efficient at removing water from the soil, tensiometers are not ideal for use in vineyards.
Another commonly used instrument relies on the electrical conductivity of a substance changing as the water content within it changes. Gypsum is often used as the conducting material, and a block of it is buried in the soil. As the soil dries so does the block, and the change in its electrical conductance can be recorded. These sensors are more accurate in drier soils than tensiometers (Zazueta and Xin, 1994), and have common application in vineyard situations.
As an electrical output is being measured, the data can be logged and transmitted to remote stations, automating some of the monitoring process.
However, the blocks have a finite life, which is shortened when used in acidic soils, and it can be difficult to convert the conductance output into actual required amounts of water to apply (Johnston, 2000).
Other methods measure the dielectric constant of a soil (which varies with moisture content), through capacitance or time-domain reflectometry (TDR).
30 25 20 15 10 5 0 –5 –10 –15 –20
January March May July September November
February April June August October December
Month
Plant-available water in soil (mm)
Fig. 6.42. Example of the amount of plant-available water in a soil through a growing season (line) and how evapotranspiration (hatched bars), rainfall (black bars) and irrigation (white bars) affect it. At field capacity the soil has 24 mm of water available in the profile, but this dips to as low as 10 mm in July.
Capacitance is measured with a probe lowered into a tube that has been carefully installed into the soil, and TDR with stainless steel rods inserted precisely into the soil. Both of these methods measure only a small volume of soil and require precise placement of the tube/rods, but they can determine volumetric soil water content (making it easier to calculate the amount of water needed) over a wide range of values (Whalley et al., 2004; Plauborg et al., 2005).
Perhaps the most accurate method of determining soil moisture is with a neutron probe, which measures the number of neutron particles that are reflected back to a source from the soil, with a wetter soil reflecting back more neutrons. As such, this method also gives an indication of volumetric soil water content and has the added advantage of being able to measure a much larger volume of soil than capacitance or TDR methods (Zazueta and Xin, 1994).
Because of this, the tubes into which the probe is inserted do not have to be so precisely installed, leading to more consistent measurements from tube to tube. However, the cost of these machines is high, taking readings is a slower process (up to 32 s each), the unit must be operated manually and, as a radiation source is used, the operator often must be licensed. As a result of the convenience factor, there is a tendency for growers to use other methods (Nicholas, 2004).
Methods of monitoring plant water status
Other than measuring what’s in the soil, the water status of the vine can also be measured which, since it directly measures the plant rather than inferred plant status from the soil status, may be more useful. For many years a pressure chamber has been used to do this in research (Scholander et al., 1965; Waring and Cleary, 1967; Ritchie and Hinckley, 1975), and now the technology is well within the grasp of many growers (Choné et al., 2001; Williams and Araujo, 2002). With this method, a leaf is cut off the vine and the blade placed into a chamber that can be pressurized (see Fig. 6.43). The petiole of the leaf is left protruding from the chamber and the pressure inside the chamber increased (usually from a compressed gas cylinder). Since the xylem of plants is under tension the fluid inside retreats back toward the leaf blade when it is cut from the plant. As pressure is applied to the leaf blade, the fluid in the xylem is forced back up the xylem to the cut surface. When this happens, the pressure inside the chamber is equivalent to the tension that was inside the xylem before the leaf was removed. The greater the tension in the plant, the less available water and the greater the water stress.
Because there is a large variation in the water potential of plant tissues over the course of a day (Hardie and Considine, 1976), the time at which the measurement is taken must be standardized. Traditionally, pre-dawn measurements were used as this was the time at which the plants had the most available water (i.e. were under the least amount of water stress). Some
research suggests that midday measurements are more accurate (Williams and Trout, 2005), but others propose that any measurement times are indicative (Williams and Araujo, 2002) or that there are varietal differences in the response to water stress, which limit its broad application (Schultz, 2003).
As the level of tension in the xylem vessels increases (i.e. the water stress in the vine is increasing) water will be drawn out of the other plant tissues, causing a decrease in stem diameter (Klepper et al., 1971). This can be measured through the use of accurate transducers and related to vine water status (Goldhamer and Fereres, 2001; Intrigliolo and Castel, 2007).
Water movement through the plant can also be measured through water loss via leaves (stomatal conductance, Escalona et al., 2002) or from water movement up the stem (using, for example, heat-pulse methodology (see Fig. 6.44; Green and Clothier, 1988). The former technique is difficult to automate (Intrigliolo and Castel, 2007), but the latter has potential for use in commercial situations (Patakas et al., 2005).
Scheduling water application
Once the level of vine water stress can be measured, a system needs to be devised through which the optimum time for application of water can be derived. The simplest strategies involve addition of water when a threshold has Fig. 6.43. Diagram of a pressure chamber as used to evaluate plant tissue water potential.
been reached. For example, if neutron probe results show that the soil moisture is reaching the point where vines will be unable to draw water from it (or some other threshold set by the vineyard manager), then water is applied. With this system the vines are always in a situation where there is no water shortage ⫺ often an advantage where maximization of quantity is desired. However, in those situations where the amount of yield is not the main focus, or where the vegetative growth needs to be managed, a strategy that leaves the vines under some water stress is often employed.
Two examples of this are the use of Regulated Deficit Irrigation (RDI) and Partial Rootzone Drying (PRD). RDI was first used on fruit trees (Chalmers et al., 1981) and involves giving the plants less water than they use in ET. This reduces shoot growth because vegetative growth is more sensitive to water stress than is reproductive growth (Coombe and McCarthy, 2000). A basic RDI programme would be to maintain water availability until following fruit set, Fig. 6.44. A sap flow meter attached to a vine trunk. The device applies a pulse of heat to the trunk and measures the amount of time it takes for the heat to travel up the trunk to the detector. The time is related to how fast the sap is flowing and, therefore, to the rate of water used by the canopy.
then in the period of cell division in the fruit limiting the amount of water, followed by provision of adequate water supply during ripening (Nicholas, 2004; Fereres and Soriano, 2007). This results in efficient use of water while not affecting yields in comparison with a full-water control.
PRD is a type of RDI, but using spatial separation of water application rather than just lowering the amount (Dry, 1997). Water is applied to one side of a vine and the other side is left to dry out, whereupon the watered side is reversed and the process is repeated through the season. This results in a reduction of shoot growth, attributed to the production and transport of abscisic acid (ABA) from the roots to the shoots (Stoll et al., 2000). ABA has been found to decrease the stomatal conductance of the leaves, leading to reduced photosynthesis and shoot growth. There has been extensive research into the potential of PRD to maintain grape quality while not affecting yields or vine health; however, on a use of water basis, there appears to be little advantage in using PRD over RDI (Gu et al., 2004), especially considering the additional infrastructure that is needed to make PRD work.
Effective measurement of vine water status is essential for strategies that employ near to detrimental soil water deficits, as slight under-application of water can result in severe vine stress and loss of productivity, or even death (see Fig. 6.45).