Irrigation: Basic Concepts
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Water Use and Irrigation of Orchard Crops
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Almond tree water needs
• On an average California almonds need 52 acre-inches per year for an orchard
with 80% canopy coverage
• That translates to 13 Mega-liters (or Megs.) per year
• Many orchards get away with applying less water: Between 42-48 inches or
10-12 Megs
• Efficient irrigation systems
• Regulated Deficit irrigation
• Proper Irrigation Scheduling (matched to soil type and Evapotranspiration,ET)
Duration ET0 Kc (Crop Etc Gallons/day Liters/day/ Liters/day/ Megaliters
(inches) Coefficient) (inches) /acre acre Ha
One day 0.32 1.15 0.37 9993 37772 94431 0.1
(June 30)
Weekly Super Almond LLC © Dr. Gurreet Brar271488
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What is
evapotranspiration (ET)?
• It is sum total of
• Evaporation (from the soil)
and transpiration (from the
leaves)
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Determining total water demand of the trees
We calculate ET.
ET is affected by environmental conditions, like
• Temperature,
Humidity,
• Solar radiation,
• Wind speed,
• Cover crop…
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Evapotranspiration
Crop Factors Management Factors
• Crop • Disease
• Cultivar • Insects
• Phenology→ Stage • Fertility
of Development • Salinity
• Height • Irrigation System
• Planting Design • Planting Design
• Rooting Depth and • Soil Water Content
Profile • Ground Cover (Cover Crops)
Characteristics (AW) • Windbreaks
• Ground Cover • Mulches
(Cover Crops)
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Water use changes throughout the year
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ET changes with age
Almond tree canopy size increases from year 1 to fully mature tree size by
year 7-8
Tree canopy does not change much over the rest of the life
ET increases considerably during first 6-7 years, then does not vary much
(unless other factors vary)
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How Does Climate Dictate Water Use in Orchards
kc values for Prunus sp. (Cold Winter/Light Frost: No
Dormancy for Ground Cover) Humid Light Wind
Dry Strong Wind
1.4
1.2
1
kc value
0.8
0.6
0.4
0.2
0
24-Jan 4-Mar 12-Apr 21-May 29-Jun 7-Aug 15-Sep 24-Oct 2-Dec
FAO Irrigation and Drainage Paper, No. 24, 1977
• Crop Water Use (ETc) is estimated by ETc = Kc * ET0
• Prunus sp. will differ in their seasonal water use, ex. Almonds vs. Peaches
• Canopy Development leads to increased radiation interception
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Irrigation Scheduling
What do you need to know?
• Know your system output: How much water you can apply per hour?
• Know your soil type: How much water your soil can hold?
• Know you system’s efficiency (Flood vs drip vs sprinkler etc.)
• Know your tree’s daily water needs
The biggest part is to know tree’s daily water needs.
We use ET calculations for that
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Drought Stress Excess Moisture
• Kernel Shrivel Leaching of Nitrogen
• Nut size reduction Water logging
• Wilting Fungal diseases
• Defoliation Water wastage
• Shoot growth Energy wastage
inhibition
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Determining water needs
• Soil based methods
• Visual/touch method
• Soil Moisture Probes
• Weather based methods
• Plant based methods
• Pressure chamber
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Checking your soil moisture
• Visual/touch
method
• Making a ball;
ribbon
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Touch/feel method
• Sand: Loose, single grained; Dry- falls apart,
crumbles
• Sandy loam: High % sand, but enough clay/silt to
be cohesive
• Loam: Relatively even mixture of sand, silt & clay
• Silt loam: high %age of silt, forms a cast easily
• Clay loam: Fine textured, breaks into clods &
lumps; thin ribbon
• Clay: fine textured; plastic & sticky, forms long
ribbon
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Know your system water application rate
• For flood irrigation you can calculate based on your pump output
• For drip or micro irrigation systems, the output/system application
rate will be written in your design documents
• Commonly, one fan jet applies about 38 liters per hour
• Common Drip emitter output is 2 liters per hour per emitter
• You can calculate how many trees you have per hectare
• You know how much the tree to tree spacing is
• You can calculate how many drip emitters you have for each tree
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For flood and furrow irrigation…
• We will simply calculate how much water the trees need daily
• And then apply that much water to the trees, after factoring in the
system losses
• (Flood or furrow irrigation system usually have 35-40% losses in deep
percolation etc.)
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Calculating number of trees per hectare
• Example:
• Row to row spacing=6 meters
• Tree to tree spacing within a row=4 meters
• Multiply these two: 6 x 4=24
• Number of square meters in one hectare=10000
• Divide 10000 by 24
• =10000 / 24=~417 trees per hectare
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MeteoBlue ETo Data: Real Time ET
Station# Target Date Target ETo(in) Previous Year
Average
ETo(in)
ETo
2 1-Jun-15 0.31 0.3 0.27
2 2-Jun-15 0.32 0.39 0.27
2 3-Jun-15 0.28 0.32 0.27
2 4-Jun-15 0.29 0.26 0.27
2 5-Jun-15 0.28 0.31 0.27
2 6-Jun-15 0.3 0.32 0.28
2 7-Jun-15 0.32 0.32 0.28
2 8-Jun-15 0.35 0.35 0.28
2 9-Jun-15 0.32 0.38 0.28
2 10-Jun-15 0.26 0.33 0.28
2 11-Jun-15 0.26 0.31 0.28
2 12-Jun-15 0.32 0.34 0.28
2 13-Jun-15 0.34 0.3 0.28
2 14-Jun-15 0.34 0.31 0.28
2Super15-Jun-15
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16-Jun-15 4.6 4.86 4.15
Calculating water needs
ETc = ETo X Kc
Crop Reference Crop
Evapotranspiration Evapotranspiration Coefficient
Irrigation system output
Irrigation efficiency
Soil water holding capacity
Calculate how much water to apply
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ET based scheduling
1. Irrigation frequency
2. Determine the Crop ET
3. Calculate the irrigation amount
In almonds, during peak water demand (June-July):
-Drip irrigation systems are run daily
-Microsprinkler every 2-4 days
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ETc = ETo X Kc
Evapotranspiration Reference Crop
Coefficient Evapotranspiration Coefficient
Almond crop coefficient
Month With cover crop Without cover crop
Dec-Jan 0.85 0
Feb 0.85 0
Mar 0.85 0.50
Apr 0.95 0.70
May 1.05 0.85
Jun/Jul/Aug 1.15 0.90
Sept 1.10 0.80
Oct 0.90 0.75
Nov 0.85 0.65
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The Almond Production Manual, UCANR
Day ET0 Kc ETc
Calculating 1-Jun-15 0.31 1.15 0.36
water needs 2-Jun-15
3-Jun-15
0.32
0.28
1.15
1.15
0.37
0.32
4-Jun-15 0.29 1.15 0.33
5-Jun-15 0.28 1.15 0.32
June 1-15= 5.29 inches 6-Jun-15 0.3 1.15 0.35
7-Jun-15 0.32 1.15 0.37
Daily water use: 8-Jun-15 0.35 1.15 0.40
5.29/15 = 0.35 in/day
9-Jun-15 0.32 1.15 0.37
10-Jun-15 0.26 1.15 0.30
11-Jun-15 0.26 1.15 0.30
12-Jun-15 0.32 1.15 0.37
13-Jun-15 0.34 1.15 0.39
14-Jun-15 0.34 1.15 0.39
15-Jun-15 0.31 1.15 0.36
4.6 5.29
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Irrigation system efficiency
Irrigation system Efficiency of
Irrigation (%)
Basin/flood 65-80
Furrow 65-75
Solid set sprinkler 75-85
Micro-sprinkler 85-90
Drip 90-95
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Calculating water needs
ETo X Kc
ETc =
Irrigation Efficiency
Example: Previously calculated ETc of 0.35 in/day with 90% efficiency
Actual water need= 0.35/0.9 = 0.38 inches/day
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Know how much water your soil can hold
• Depends on soil type; soil texture
• Don’t apply more water that this capacity in a single irrigation set
Soil Texture Water Holding Capacity (mm per Average
foot of soil profile) (mm/foot)
Very Course 15-25 19
Sandy, Sandy Loam 25-38 32
Loamy, Silt clay loam 32-56 38
Fine soils, Clay 43-61 51
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Don’t forget soil’s water holding capacity
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Source:http://soilwater.com.au/bettersoils/module2/2_1.htm
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What next?
• You know your system output (gallons per hour)
• One acre inch=~27000 gallons
• Calculate the runtime!
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Important factors to keep in mind
Ground cover
Irrigation distribution uniformity
Irrigation timing
System Efficiency
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Using Available Water, how can you calculate the total water holding capacity of a profile
Almond Root zone depth ~4 feet
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Allowable Depletion
The ‘safe’ amount of
depletion as a percentage of
total available water in the
profile
In the field a value of ~50%
is assumed to be the
maximum AD
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Plant based monitoring
• Pressure Bomb
• Complements ET-based scheduling
• Stem water potential
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How does it work ?
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Interpreting the readings
Bars 0 Almonds Walnuts Prunes/Plum
-2 {Fully irrigated.
{Low stress.
Root Disease risk} Excellent early season}
-4
{Low to mild.
Leafout to mid June}
-6
{Mild-Moderate.
{Low stress.
Shoot growth } {Low stress.
-8 Shoot
growth} Ideal shoot growth}
-10 Severe {Moderate. Shoot
{Mild-
Moderate. stress growth may }
-12
Before hull
split} Wilting,
-14 defoliation
{Moderate.
Can tolerate during
-16 hull split}
High High
-18
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(Re-drawn from: UCCE Guidelines info@superalmond.tech
for interpreting pressure chamber readings)
Irrigation strategies
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Irrigation Strategies: (example of Almonds)
Severe Deficit in this
period will increase
Deficit in this period will
shriveled nuts
decrease nut/fruit size
Deficit in this period will
increase “texturing”, decrease
kernel weight
Deficit in this period has
minimal effects
Deficit in this
period effects
fruit bud set
Stress at any period reduces vegetative growth,
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Irrigation Strategies
100
Stress started here, in
effect for 3 weeks
80
% of Kernel Weight
60
Stress started here,
affect entire season
40
Full Irrigation
RDI
20
Drought @75% Etc
0
2 3 4 5 6 7 8 9
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Almonds: regulated Deficit Irrigation
Stage RDI?
Leafout & Nut growth No
Mid June – Hull split 50%
At Hull split No
Post harvest Maybe
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www.superalmond.tech info@superalmond.tech Jack Kelly Clark, UCANR
Almonds RDI
• Hastens Hull Split
• Hull rot Photo: David Doll
• No yield reduction
• Overall 13 % water use savings
Must provide water at hull split
2/5/2022
Source: http://ucmanagedrought.ucdavis.edu; Stewart et al.,LLC
Super Almond 2011
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Contributors: A. Fulton, R. Buchner, D. Goldhamer, B. Lampinen,info@superalmond.tech
www.superalmond.tech T. Prichard, L. Schwankl and K. Shackel
A drought spell scenario
Mature Orchard, 2003-2012
4000 2012: Full ETc was
matched, normal
3500 production
3000
2500
2000 2011: Full ETc was
2009: Severe Curtailment matched, near normal
1500 on West side, 12” of production
applied water
1000
2010: Full ETc was
500 matched
0
2002 2004 2006 2008 2010 2012 2014
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