Topic 5 - Introduction to water, soil and the vine Flashcards
(174 cards)
1
Q
What is water potential (Ψ)?
A
A measure of the free energy of water per unit volume relative to a standard state, usually expressed in bars or Pascals.
2
Q
How does water move in a plant according to water potential?
A
Water moves passively from areas of high water potential (less negative) to low water potential (more negative).
3
Q
What is the typical direction of water movement in grapevines?
A
From wet soil (higher Ψ) to the atmosphere (lower Ψ), through roots, stems, leaves, and berries.
4
Q
What are the typical values of water potential in the grapevine transpiration system?
A
All water potential values are negative.
5
Q
Why is measuring grapevine water potential important?
A
To determine vine water status and quantify water stress.
6
Q
What percentage of water taken up by roots is lost via transpiration?
A
95% - 99%.
7
Q
What is the transpiration stream?
A
The movement of water through the vine, exiting via stomates on leaves and berries.
8
Q
What is the formula for total water potential (Ψ)?
A
Ψ = Ψπ + ΨP + ΨM + Ψg.
9
Q
What is Ψπ (osmotic potential)?
A
Determined by solute concentration; higher solutes = lower Ψπ; major component of Ψ.
10
Q
What is ΨP (hydrostatic potential)?
A
Pressure from living cells (positive turgor) or xylem tension (negative); major component of Ψ.
11
Q
What is ΨM (matrix potential)?
A
Water potential related to adhesion of water to surfaces.
12
Q
What is Ψg (gravitational potential)?
A
Potential related to water’s position in a gravitational field.
13
Q
What is the permanent wilting point in grapevines?
A
Around -1.5 MPa, where xylem tension fails and water transport stops.
14
Q
What is turgor pressure?
A
Hydrostatic pressure in living cells driving cell expansion.
15
Q
What happens when leaf turgor pressure reaches zero?
A
The leaf wilts due to reduced internal pressure under water stress.
16
Q
How is turgor pressure maintained?
A
By regulating osmotic potential through solute accumulation.
17
Q
When does leaf water potential reach its lowest point?
A
Around solar noon (mid-day), indicating maximum water stress.
18
Q
What does pre-dawn leaf water potential represent?
A
It approximates soil water potential in the rootzone.
19
Q
When is vine water potential highest?
A
From pre-dawn to shortly after sunrise.
20
Q
Does transpiration stop at night?
A
No, it slows down but continues through stomates and cuticle.
21
Q
What is the Cohesion Tension Theory?
A
It explains water movement in plants through cohesion between water molecules and tension from transpiration, forming a continuous water column.
22
Q
Why doesn’t capillary action contribute to water lifting in grapevine xylem?
A
Because grapevines have large xylem vessels that cannot sustain water columns by capillary action.
23
Q
What factors influence water movement in grapevines?
A
Soil water availability and atmospheric conditions (e.g., transpiration).
24
Q
What is transpiration?
A
The loss of water from grapevine leaves and berries, mainly through stomates.
25
What influences transpiration rate?
Solar radiation, vapour pressure deficit, wind, stomatal and diffusion resistance.
26
What controls stomatal pore size?
The swelling and shrinking of guard cells, triggered by changes in turgor pressure.
27
What is stomatal conductance?
The rate of water vapor movement through stomates, proportional to stomatal aperture.
28
How is stomatal conductance measured?
With a porometer.
29
How does leaf water status affect stomatal conductance?
Low water potential increases ABA, causing stomates to close.
30
How does soil dryness affect stomatal conductance?
Dry soil induces ABA synthesis, reducing stomatal conductance.
31
How does CO2 concentration affect stomatal conductance?
Low CO2 inside the leaf opens stomates; high CO2 closes them.
32
What is the effect of high vapour pressure deficit on stomatal conductance?
It increases transpiration and leads to stomatal closure.
33
How does light affect stomates?
Stomates are more sensitive to blue light, affecting opening.
34
How does temperature affect stomatal conductance?
High temperature can increase transpiration but has variable effects on stomatal conductance.
35
What influences the root:shoot ratio in grapevines?
Soil water restriction increases it; shoot trimming affects root structure.
36
What is sap flow?
The movement of water and minerals through xylem from roots to shoots.
37
What determines sap flow rate?
The difference in water potential divided by hydraulic resistance.
38
Where does the greatest water movement resistance occur?
At the soil-root and leaf-air interfaces.
39
What is cavitation in xylem vessels?
The collapse of water tension by air bubbles, leading to embolism.
40
What causes cavitation?
Freezing, water stress, or air entry through pit membranes.
41
What happens if cavitated vessels are not refilled?
Water flow to leaves stops, causing leaf death.
42
When is grape berry transpiration highest?
Pre-veraison, and higher during the day than at night.
43
What is the dominant water transport route in berries pre-veraison?
Xylem transport.
44
What happens during post-veraison berry development?
Phloem transport increases, xylem slows, and transpiration decreases.
45
What causes berry splitting?
Rapid water uptake exceeding skin elasticity, often during rain and low transpiration.
46
Which varieties are more prone to berry splitting?
Thin-skinned varieties like Semillon and Riesling.
47
What management can reduce fungal risk from berry splitting?
Improving canopy ventilation to dry berries faster.
48
When do berries expand more, day or night?
At night; they may contract during the day.
49
What is evapotranspiration (ETV)?
The combined water loss from soil evaporation and plant transpiration in a vineyard.
50
How is reference crop evapotranspiration (ET0) used to estimate vineyard ETV?
ET0 is adjusted using a crop coefficient to estimate site-specific ETV.
51
What is the alternative method to estimate ETV besides ET0?
Using water loss from an evaporation pan (ETp) and a crop factor.
52
What is the formula to calculate vine water use?
Vine water use (ETV) = crop coefficient × ET0 = crop factor × ETp.
53
When is irrigation required in vineyards?
When ETV exceeds rainfall.
54
Why might viticulturists apply less water than calculated irrigation needs?
To align with production goals and based on grower experience.
55
What factors influence modern irrigation strategies?
Historical application, evaporative demand, soil moisture thresholds, and plant water status thresholds.
56
What are vine water needs from budburst to flowering?
Water supports root/shoot growth and leaf function. Often met by winter/spring rain.
57
Why avoid water stress from budburst to flowering?
It causes irregular budburst, poor shoot growth, and reduced flowering and fruit set.
58
When might early irrigation be necessary in the season?
In dry winters or warm regions to avoid pre-flowering water stress.
59
What are vine water needs from flowering to veraison?
Supports shoot/root growth, leaf function, flowering, fruitset, and berry growth.
60
Why is water stress after fruitset potentially beneficial?
It limits excessive shoot growth and canopy shading.
61
What are the risks of excessive water supply after fruitset?
It can lead to vigorous growth, shading, and reduced fruitfulness next season.
62
What are vine water needs from veraison to harvest?
Supports shoot/root growth, leaf function, and berry growth.
63
What happens if water is excessive after veraison?
Shoot growth competes with berries for carbohydrates and delays ripening.
64
What are the effects of moderate water stress post-veraison?
Smaller berries with higher sugar and phenolic concentration due to higher skin-to-pulp ratio.
65
What are the effects of severe water stress post-veraison?
Reduced berry size, yield, delayed sugar accumulation, and impaired flavour development.
66
What are vine water needs post-harvest?
Water supports root growth and leaf function.
67
What are the risks of severe water stress post-harvest?
Early leaf fall and inhibition of second root growth flush, limiting carbohydrate reserves.
68
Why are soil water content measurements preferred for irrigation scheduling?
They account for site-specific factors like variety, soil type, and rainfall.
69
What does soil moisture tension indicate?
The force binding water to soil particles, indicating how easily roots extract water.
70
What is drainage in soil water content terms?
Water that drains out of soil after saturation, not held by soil particles.
71
What is field capacity?
Water content remaining in soil after drainage, typically at 2–10 kPa tension.
72
What is the permanent wilting point?
Soil water tension (~-1500 kPa) where leaves wilt irreversibly without rehydration.
73
What is total available water (TAW)?
All water a vine can extract, including under stress and post-stress limits.
74
What is readily available water (RAW)?
Soil water that can be extracted without vine stress, usually irrigated at 40–60 kPa.
75
What is deficit available water (DAW)?
Water extracted under increasing vine stress, up to 400 kPa.
76
What is vine-available water (VAW)?
VAW = RAW + DAW; determined by soil texture.
77
What happens when RAW is depleted?
Vines extract DAW, experiencing increasing water stress.
78
What are signs of water stress in grapevines?
Lower leaf water potential, reduced stomatal conductance, photosynthesis, and transpiration.
79
What does stem water potential between -0.1 to -0.5 MPa indicate?
No or low water stress; vines perform at physiological potential.
80
What does stem water potential between -0.5 to -1.0 MPa indicate?
Decreased transpiration and conductance; drought adaptation and minor yield impact.
81
What does stem water potential between -1.0 to -1.5 MPa indicate?
Moderate stress; ABA synthesis begins, possible slight yield penalty.
82
What does stem water potential between -1.5 to -2.5 MPa indicate?
Leaf embolisms; stem embolisms begin beyond -1.7 MPa.
83
What does stem water potential below -2.5 MPa indicate?
Extensive embolism, risk of vine mortality and crop loss.
84
What is a near-isohydric grapevine?
Maintains stable water potential despite declining soil moisture.
85
What is a near-anisohydric grapevine?
Allows water potential to drop with declining soil moisture.
86
What traits are now proposed to describe vine water stress response?
Max transpiration rate, stomatal regulation, turgor loss point, root volume.
87
What must a grower consider when planning irrigation scheduling?
Production goals, intended wine style, and grape variety.
88
What characterizes a 'no water stress' irrigation strategy?
Soil water is maintained within RAW range; vine shows no signs of water deficit.
89
What are potential downsides of no water stress irrigation?
May lead to excessive shoot growth and canopy shading.
90
What is Sustained Deficit Irrigation (SDI)?
Water supply is limited for the remainder of the season from a chosen point (often post-fruitset).
91
What level of water stress is maintained under SDI?
Mild to moderate water stress.
92
What is Regulated Deficit Irrigation (RDI)?
Water is restricted for a set period post-fruitset, then restored to maintain RAW.
93
How is water applied under RDI?
Short irrigations maintain soil water at a targeted deficit level, then full irrigation resumes.
94
What level of stress is targeted under RDI?
Typically mild to moderate, but may vary depending on conditions.
95
What is Partial Rootzone Drying (PRD)?
Alternating irrigation between sides of the rootzone to induce ABA production and regulate stomatal aperture.
96
How often is irrigation switched in PRD?
Every 3–14 days, depending on soil type and weather.
97
What is the role of ABA in PRD?
ABA from drying roots reduces stomatal aperture, lowering transpiration and shoot growth.
98
What are the physiological outcomes of PRD?
Lower stomatal conductance and shoot vigour, minimal impact on leaf water potential and berry weight.
99
What is a major advantage of PRD?
Improved water use efficiency with minimal yield loss and reduced risk of severe water stress.
100
What are limitations of PRD related to soil and drainage?
Poor drainage may keep roots too wet; clay soils may not dry well; free-draining soils are ideal.
101
What is critical for successful PRD scheduling?
Regular monitoring of soil moisture and vine stress to properly time irrigation switches.
102
Why is limiting water availability sometimes necessary in vineyards?
To reduce excessive vigour and dense canopies in fertile, high water-holding soils.
103
How can ground cover reduce vine water availability?
By creating competition for soil water between vines and cover crops.
104
What is the effect of cover crops on canopy density?
They reduce water availability, which may reduce canopy density.
105
What is root pruning and its purpose?
Trimming roots to reduce soil volume for water uptake; a short-term solution to control vigour.
106
Why is water conservation important in Australian vineyards?
Because water is a limiting resource in most regions.
107
How does slashing or mowing cover crops help conserve water?
It reduces competition between cover crops and vines for water.
108
How does mulching help conserve soil moisture?
By reducing evaporation from the soil surface.
109
What is the function of vineyard catchment areas?
To harvest and retain water within the vineyard.
110
How can plastic sheeting be used for water conservation?
To harvest and direct water into the vine rows.
111
Why use soil moisture monitoring for irrigation scheduling?
To apply irrigation more precisely and efficiently.
112
What are the benefits of matching rootstocks to soil and irrigation?
It optimizes vine water use and improves vineyard performance.
113
How can dam evaporation be reduced?
By covering the surface of dams.
114
What are the benefits of sub-surface irrigation?
It reduces water loss via evaporation.
115
What is a limitation of sub-surface irrigation?
Difficult to monitor for leaks and check drippers.
116
How can mulch improve sub-surface irrigation efficiency?
By covering dripper lines and further reducing evaporation.
117
How does precision viticulture help conserve water?
By applying water variably based on vine vigour and site variability.
118
What materials can be used for mulching?
Straw, bark, grape marc, plastic, and stones.
119
How much water can mulching save?
10–30%.
120
What are other benefits of mulching?
Improves soil structure and biology, suppresses weeds, and increases organic matter.
121
What are potential downsides of mulching?
May increase shoot length and berry size, affecting wine style.
122
What is soil salinity?
The concentration of soluble salts in soils, including Na+, K+, Ca2+, Mg2+, Cl-, SO42-, CO32-, and HCO3-.
123
What causes soil salinity?
Saline irrigation water, poor leaching, and increased aridity.
124
What are the effects of soil salinity on grapevines?
Osmotic stress limiting water uptake and ion toxicity, especially from Na+ and Cl-.
125
How can soil salinity be managed?
Use low-salinity water (<0.8 dS/m), leach salts, blend irrigation water, and use salt-tolerant rootstocks.
126
What does soil health refer to in viticulture?
The soil’s ability to support growth, nutrient uptake, and a healthy vine.
127
What improves soil biological activity?
Minimal tillage, compost, mulch, and ground cover.
128
What is the rhizosphere?
The soil zone around roots with high microbial activity essential for vine health.
129
What are key physical properties of soil?
Texture, structure, aggregate stability, and strength.
130
What is cation exchange capacity (CEC)?
A measure of how many cations soil can retain and exchange, important for nutrient availability.
131
What is the ideal pH range for grapevine nutrient uptake?
Between 5.5 and 8, ideally around 6–7.
132
How can soil acidity be adjusted?
By adding calcitic or dolomitic limestone.
133
How can soil sodicity be treated?
With gypsum application.
134
What causes soil compaction?
Machinery traffic on moist soils.
135
What are the effects of soil compaction?
Reduced root growth, waterlogging, and lower aeration.
136
How can soil compaction be reduced?
Minimize machinery use, apply mulch/compost, plant cover crops, deep ripping.
137
What is the role of macro-nutrients?
Essential for growth and reproduction; includes N, K, Ca, Mg, P, and S.
138
What are micro-nutrients?
Required in small amounts; includes Cl, B, Fe, Mn, Zn, Cu, Ni, Mo.
139
How is nitrogen (N) related to fermentation?
Low N reduces yeast assimilable nitrogen (YAN), causing stuck fermentations.
140
What is the effect of excessive potassium (K)?
Raises juice/wine pH, requiring more acid in the winery.
141
What does phosphorus (P) deficiency cause?
Reduces fruitset and yield.
142
What is calcium (Ca) important for?
Cell walls, signalling, and transported via xylem with water.
143
What causes magnesium (Mg) deficiency?
Occurs in acidic and calcareous soils; affects phloem loading and can lead to bunch stem necrosis.
144
What does molybdenum (Mo) deficiency affect?
Impairs N metabolism and phytohormone synthesis; more likely in acidic soils.
145
What is the preferred method for assessing vine nutrient status?
Tissue (petiole) analysis, especially at flowering.
146
What are benefits of petiole analysis?
Sensitive to nutrient status, region-specific standards, useful for long-term tracking.
147
Why is soil analysis less reliable?
High variability, less correlation to root uptake, and hard to sample representatively.
148
How does water loss occur from vineyards and how can the potential water loss, and irrigation requirements be estimated?
Water loss in vineyards occurs through evapotranspiration (ETV)—the combined effect of evaporation from the soil and transpiration from grapevines and mid-row vegetation.
ETV can be estimated using:
Reference evapotranspiration (ET₀) from a standard crop (e.g. grass), adjusted by a crop coefficient specific to grapevines.
Evaporation pan (ETp) measurements, adjusted using a crop factor.
Irrigation requirement is calculated as:
Vine water use = crop coefficient × ET₀ = crop factor × ETp
Rainfall is subtracted from this to estimate net irrigation need.
149
Explain grapevine water requirements at different stages of the season and how water stress could affect vine development during these stages.
Budburst to flowering: Water is needed for root/shoot growth and leaf function. Water stress can lead to irregular budburst, reduced shoot and leaf growth, and poor fruit set.
Flowering to veraison: Supports active growth, flowering, and berry development. Water stress can reduce berry size and yield, while excessive water can cause vigorous growth and poor canopy microclimate.
Veraison to harvest: Moderate stress is often desirable to limit shoot growth, enhance fruit concentration, and control berry size. However, severe stress can delay ripening and reduce sugar and phenolic development.
Post-harvest: Water is required for carbohydrate storage and root growth. Stress at this stage may cause early leaf drop and weakened vines in the following season.
150
Discuss strategies that could be used to conserve water during dry periods and to avoid salinity problems in vineyards.
Water conservation strategies:
Mulching to reduce evaporation and enhance soil structure.
Slashing/mowing cover crops to reduce competition for water.
Precision irrigation techniques (e.g. SDI, RDI, PRD) and soil moisture monitoring.
Sub-surface irrigation to minimise surface evaporation.
Harvesting rainwater and constructing vineyard catchments.
Salinity management:
Use low-salinity irrigation water (EC < 0.8 dS/m).
Leach salts from the rootzone with irrigation/rainfall.
Blend high and low salinity water if needed.
Plant salt-tolerant rootstocks (e.g. Ramsey, 1103 Paulsen).
Avoid overhead irrigation, which increases Na+ and Cl– on berries.
151
Describe the problems of too high or too low nutrient availability on vine growth and development.
Deficiencies limit vine growth, yield, and berry quality. For example:
Low N: Poor shoot vigour and low YAN (risk of stuck fermentations).
Low P: Reduced fruit set.
Low Mg: Bunch stem necrosis.
Low Mo: Impaired nitrogen metabolism and hormone synthesis.
Excesses may be toxic or cause imbalanced growth:
Excess N: Shaded canopy, high juice pH, reduced aroma and colour.
Excess K: Elevated juice/wine pH, requiring acid addition.
Micronutrients in excess (e.g., Fe, Zn, Cu) can be toxic even in small amounts.
Balanced nutrition is vital, and nutrient status is best assessed by petiole analysis, supported by soil tests and visual vine assessment.
152
What is transpiration efficiency (TE)?
The total carbon fixed by photosynthesis divided by the amount of water transpired (kg dry matter/kg water).
153
Name two vineyard management practices to improve water use efficiency.
(1) Use less water via efficient irrigation scheduling. (2) Improve dripper and sprinkler uniformity.
154
What is wine value water use efficiency (WUEwv)?
The economic value of wine produced per unit of water used.
155
156
What are the three main approaches for determining irrigation timing and amount?
Climate-based, soil-based, and plant-based methods.
157
Which method gives the most accurate information about vine water stress?
Plant-based methods.
158
Which method provides the best estimate of how much water to apply?
Soil-based methods.
159
What is the advantage of combining plant and soil-based methods?
It provides the most comprehensive data for irrigation scheduling.
160
How does the evaporation pan method estimate evapotranspiration?
ET = pan evaporation × crop factor.
161
How do weather stations estimate evapotranspiration?
They use temperature, humidity, wind, and radiation data with a crop coefficient.
162
What are two main soil-based targets for irrigation scheduling?
Soil moisture tension and volumetric water content.
163
How do tensiometers work?
They measure suction required to extract water, operating between 0 and -80 kPa.
164
How do electrical resistance blocks work?
Resistance between electrodes increases as soil dries; operate between -60 and -600 kPa.
165
How do capacitance probes measure soil water content?
They detect changes in dielectric constant via resonant frequency of electric fields.
166
What is the principle of TDR in soil moisture measurement?
Measures time delay of electromagnetic pulse related to soil dielectric constant.
167
How do neutron probes estimate soil water content?
By counting slowed neutrons after collision with hydrogen in soil water.
168
What does the heat pulse method measure?
Time taken for heat to dissipate, indicating soil water content.
169
What does leaf and stem water potential measure?
The suction the vine exerts on soil water, using a pressure chamber.
170
How is stem water potential measured differently from leaf water potential?
The leaf is bagged for 1 hour to reflect xylem pressure before measurement.
171
What does stomatal conductance indicate?
Resistance to water vapour loss; it decreases under water stress.
172
How does leaf temperature relate to vine water stress?
Water stress reduces transpiration, increasing leaf temperature.
173
What does sap flow measurement show?
The rate of water flow through the trunk; it declines under water stress.
174
What can trunk diameter changes indicate?
Vine water status; used in research and can be automated.
