Irrigation and Salinity Management of AvocadoDavid Crowley

Dept of Environmental Sciences, University of California, Riverside

New Technologies for Avocado Production

Improved rootstocks for salinity tolerance

Soil inoculation with PGPR (plant growth promoting rhizobacteria)Control of phytophthora root rotProduction of plant growth hormonesSuppression of stress ethylene

Improved water use efficiencyImproved salinity tolerance

Online Decision Support ToolsIrrigation and Fertilizer ManagementNeural network based disease and yield forecasting models

Use of charcoal (biochar) amendmentsImproved CEC, pH, bulk density, soil structureImproved water holding, aeration, root growthIncreased microbial activity

Soil and Water Management(Topics for Today)

Irrigation Irrigation scheduling – CIMISImportance of adjusting for soil textureWater quality and salinity management

Results of the CAC Salinity Research ProjectRoot stocks selectionsChloride effects on root growth and yieldComputer guided decision support tools

The ideal soil: no stress for air or water, good soil structure, low bulk density, supports beneficial microbial activity, root growth

Irrigation Scheduling

The Water Budget:

Field Capacity: How much water does your soil contain after being saturated and allowed to drain?

Available water: What fraction of the water can be taken up by plants?

Yield threshold depletion: When does water depletion affect yields?

Managed allowed depletion: At what water level does the grower irrigate?

Soil moisture depletion: Amount of water needed to return to field capacity

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California Irrigation Management Information System (CIMIS)

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ET of California Avocado Soils

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Grapevines 0.80

Stone fruits 1.05

Apple 1.05

Kiwifruit 1.05

Citrus 0.67

Citrus (desert) 0.60

Olives 0.70

Avocado 0.70

Evergreen 0.60

Crop Coefficients (Kc)

Calculation of Water Requirements for Vegetable and Tree Crops

If, ETo = 0.25 inches/day and, Kc = 0.55 (for an orange tree in July) then, ETc = ETo x Kc = 0.25 inches/day x 0.55 = 0.1375 or 0.14 inches/day

ETo X Kc = inches / day

San Luis Obispo – Central Coast Station 52

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Irrigation and Water Use Efficiency

The Role of Soil Texture (Sand, Silt, Clay)

Aggregates: Cemented units of soil particles and organic matter.

In structureless soil,%

In structured soil,%

Porosity 50 55-60

General porosity 45-48 20-25

Capillary porosity 2-5 30-35

Noncapillary porosity 5 30-40

Air content 3-5 20-25

Water permeability(in mm/hr)

1.6 0.7

Microaggregates

Capillary pores

Soils Used for Avocado Production in California

Physical Properties

Texture Sandy to Heavy ClayBulk Density 1.2 – 1.6 g/cm3

Porosity 20% to 50%Stable Aggregates 5% to 30%

Chemical PropertiespH 5 – 8Cation Exchange 2 – 30 meq / kgOrganic Matter 0.1 – 4%

Finding your soil: USDA Web Soil Survey

Finding your soil: USDA Web Soil Survey

Field Capacity Permanent Wilting Point

Water holding capacity as affected by soil texture

Sandy textured soils will hold very little water and need morefrequent irrigation cycles

Measurement of Soil Water Potential

TensionmeterAbsorbent BlocksTime Domain Reflectometery (TDR)

Root Depth Distribution and Water Use by Avocado

Water Mark Probes

1. Soil temperature2. Tree 1 6 inch3. Tree 2 6 inch4. Tree 3 6 inch5. Tree 1 12 inch6. Tree 2 12 inch7. Tree 3 12 inch8. Tree 1 24 inch

Water Mark Probes

1. Soil temperature2. Tree 1 6 inch3. Tree 2 6 inch4. Tree 3 6 inch5. Tree 1 12 inch6. Tree 2 12 inch7. Tree 3 12 inch8. Tree 1 24 inch

Quality Electrical

Conductivity

(millimhos/cm)

Total Salts

(ppm)

Sodium

(% of

total

salts)

SAR pH

Excellent 0.25 175 20 3 6.5

Good 0.25-0.75 175-525 20-40 3-5 6.5-6.8

Permissible 0.74-2.0 525-1400 40-60 5-10 6.8-7.0

Doubtful 2.0-3.0 1400-2100 60-80 10-15 7.0-8.0

Unsuitable >3.0 >2100 >80 >15 >8.0

Suitability of Water for Irrigation

The Problem with Total Dissolved Salt: High Salt Inhibits Plant Water Uptake

Water enters the plant by osmosisSalt in the soil sucks water out from the plant roots

For avocado, this occurs at EC = 4 dS/m

0

5

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25

30

0 10 20 30 40 50 60

EC 4 No available water

EC 0.5EC 1.5EC 2.5EC 3.5

Plant Available water

Volumetric Water Content

Sal

inity

EC

Por

e W

ater

water water everywhere, but nothing ….

Avocado is one of the most saline sensitive crops, and is subject to yield reduction when irrigated with saline irrigation water. This is due to a combined effect of dissolved solids (EC) and chloride toxicities.

http://www.umanitoba.ca/afs/agronomists_conf/2002/pdf/cavers.pdf

Avocado Yield Function for Irrigation Water SalinityOster and Arpaia, J. Am Soc. Hort Sci. 2007

100

80

60

40

20

0Rel

ativ

e Yi

eld

(%)

0.5 1.0 1.5 2.0 2.5 3.0

Salinity (EC)

320 640 960 1280 1600 1920

TDS (ppm)

Irrigation Water Salinity

Salts in irrigation water include toxic minerals:

Cations Anions

Calcium Ca++ Sulfate SO42-

Magnesium Mg++ Carbonate CO32 -

Sodium Na+ Chloride Cl -Potassium K+

Chloride Sodium

Uptake and Distribution of Radiolabeled Chloride and Sodium (Kadman ca 1960s, avocadosource.com)

Combined Effects of Chloride and Sodium Toxicity

Chloride 0.58% Chloride 0.61%Sodium 0.35%

Effects of Chloride Toxicity on Root Growth

7 49 915 mM NaCl 15 mM NaCl 25 mM NaCl

Elapsed time under salinity (days)

Roo

t elo

ngat

ion

rate

(m

m /

day)

3

2

1

0

100

50

0

% of control

saltcontrol

100%

57%

25%

Berstein (Avocadosource.com)

Would you put this on your orchard?

1 Acre Foot = 1,233,000 Liters

TDS = 500 mg / Liter

615 kg of TDS Salt

X

How Much Salt is in Your Water?

1 Acre Foot = 1,233,000 Liters

Na - 54 to 101 mg/L Cl - 71 to 96 mg /L

66 - 124 kg Na87 - 118 kg Cl

153 - 242 kg NaCl

X

How Much Sodium Chloride is in Your Water?

4 Acre Feet:

612 - 968 kg NaCl

2464 kg total dissolved salt

How Much Salt is in Your Water?

Measuring Salinity: Electrical Conductivity

Units for measuring salinity, and conversion factors.

Conversion factors relating total dissolved salts or pure NaCl to an electrical conductivity (EC) of 1 dS/m (1 deciSiemen/metre) are given, along with equivalent units of various types, old and new. The conversion of EC of 1 dS/m to total dissovled salts (640 mg/L) assumes a composition of salts that is common in groundwater across the world. The exact factor varies from 530 (if the salt is predominantly NaCl) to 900 (if the salts are formed predominantly from divalent ions).

Measurement and units

Application 1 dS/m is equal to:

Equivalent units

Conductivity (dS/m) soils 1 1 dS/m = 1 mS/cm = 1 mmho/cm

Conductivity (µS/cm)

irrigation and river water

1000 µS/cm 1 µS/cm = 1 µmho/cm

Total dissolved salts (mg/L)

irrigation and river water

640 mg/L (approx.)

1 mg/L = 1 mg/kg = 1 ppm

Molarity of NaCl (mM)

laboratory 10 mM 1 mM = 1 mmol/L

Example of an EMI Survey MapHigh conductivity readings are expected where a heavy clay soil is seasonally waterlogged with saline ground water (red to pink colours on an EMI survey map); and Low conductivity readings can be expected in dry, sandy soils (or gravel), with little clay and almost no salt (blue to green).

Salt Accumulation in Tree Crop Orchards Using Drip Irrigation

Salt Accumulation in Tree Crop Orchards Using Micro-Spray Irrigation

CDWR 2003

Soil Leaching: Pushing Salt Down

Leaching Fraction

Soil

ECe

(dS/

m)

Irrigation Water ECiw (dS/m)

0 2 4 6 8 10

10

8

6

4

2

0

0.05 0.10 0.15 0.20

Leaching Fractions

TDS/Conductivity/Salinity Pen

Collect Soil Cores0-6”, 6-12”, 12-18”

Prepare 2:1 Water:Soil ExtractsDistilled Water

Measure ECMultiply x 6 (to estimate soil ECw)

If EC > 0.25 dS m-1 for 2:1 water extract then it is time to leach (equivalent to an ECw of 2.0 at field capacity)

Dealing with Salinity

Proper Irrigation Management

Gypsum

Leaching

Organic Matter

Rootstock Selection

High Ca++, Mg++

Low Ca++, Mg++

Calcium and magnesium help soil particles stick together; Sodium causes the soil particles to disperse.

Low Sodium High Sodium

Consequences of Soil Dispersion

Poor Drainage: Less infiltration of waterIncreased water runoffLess efficient leaching of salt

Loss of Soil StructureLoss of soil pore spaceDecreased oxygenIncreased soil erosion

Plant Effects High soil bulk density Decreased root growthAnoxia and root death

Loss of soil structure leads to a spiral effect that results in

decreased soil quality, poor plant growth,

root disease, low yields.

Poor water infiltration leads to soil ponding: poor leaching, salt accumulation, low soil oxygen, root death from anoxia, and increased Phytophthora root rot.

Salinity: Sodium and Chloride

Good Salts: Calcium, MagnesiumHold soil particles together

Problem Salts: Sodium – soil dispersionChloride - toxicity

New Developments in Irrigation and Salinity Management

• Requirement for improved water use efficiency• Reduction / elimination of nitrate, pesticide runoff

• Irrigation water qualityDealing with salinitySoil leaching requirement

• RootstocksWhich are best for water use efficiencyWhich are best for salinity tolerance

• Computer decision support toolsAutomated soil water monitoringProduction function models for salinity, chloride

Salinity-Chloride Interactions: Their Influence on Yields

David Crowley and Mary Lu ArpaiaDept of Environmental Sciences, University of California,

Riverside, and UC Kearney Agricultural Center, Parlier, CA Cooperating Investigators: Ben Faber and Gary Bender

1. Examine salinity effects on the yields of avocado trees across the main production areas in S. California.

2. Compare salinity performance of the major rootstocks now being used for avocado production.

3. Evaluate the specific ion toxicity effects of chloride and sodium on root growth.

Objectives:

Current Research

Salinity – Chloride Interactions and Their Effects on Avocado Yields

Due to nutrient interactions that affect yield, scatter plots show no apparent relationship between chloride toxicity and fruit yields.

Yield values predicted from an artificial neural network model using fixed values for all nutrientsexcept chloride (values fixed at average levels for entire orchard: N 2.4%, P 0.18%, K 1.2%, Ca1.5%, Mg 0.4%, Na 0.015%, Zn 30 ppm, Fe 84 ppm, B 40 ppm.

Fruit yield as affected by leaf chloride content for Hass avocado grafted on to different rootstocks under “average” nutrient conditions.

Fruit yield as affected by leaf chloride content for Hass avocado grafted on to different rootstocks under “optimal” nutrient conditions.

Predicted fruit yield for trees with foliar nutrient values optimized for maximum yields, while varying leaf tissue chloride content for each rootstock. Optimized nutrient levels were N 1.7%, P 0.26%, K 1.3%, Ca 1.14%, Mg 0.28%, Na 0.015%, Zn 31ppm, Fe 100 ppm, B 40 ppm.

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Toro Cny Dusa Duke 7 Mexican Thomas

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Leaf

Chl

orid

e (%

)

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Toro Cny Dusa Duke 7 Mexican Thomas

pH 6.5pH 7.0pH 7.5

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Toro Cny Dusa Duke 7 Mexican Thomas

pH 6.5pH 7.0pH 7.5

Leaf

Chl

orid

e (%

)ANN predicted effect of changes in soil pH on leaf chloride content for five avocado rootstocks. Additional parameters were set under relatively harsh conditions that are associated with elevated chloride levels: soil ECe= 4.0 dS/m, soil Cl 8 mg/kg; irrigation water EC 0.8 dS/m; irrigation water chloride = 50 mg/L; soil clay content 50%.

Decision Support Tools for Integration of Soil Chemical Physical Properties, Root Stock Selection, and Prediction of Economic

Benefits

Questionnaire

Recommendations

Water Quality Data, Rootstocks Used

Yield Data

Soil and Climate Data

Salinity Research - Benefits to the Industry

• Cost benefit analysis for irrigation water quality versus fruit yields over the full range of salinity levels that occur in water supplies used by avocado growers.

• Optimization of irrigation regimes for use of saline irrigation waters based on management of chloride versus total dissolved salts.

• Basic information on mechanisms of salinity stress and tolerance in avocado rootstocks. Improved guidance to growers for appropriate rootstock selection.

SUBMITTED BY: CROWLEY, DAVID WORK REQ #: 03W003DANR SECTION: AGF: ENV SCI, UCR # OF SAMPLES: 2

DATE RECEIVED: 07/08/02COMMODITY: Avocado Irrigation Water DATE REPORTED: 07/26/02

DANR CLIENT #: CROX1 TURN AROUND TIME IN WORKING DAYS: 15

Sample Type: WATER Date Sampled: 24 Oct 01 & 18 May 02; Grower/Location/Project: Stehly/San Diego/ Stehly SalinityEC pH Ca (Soluble) Mg (Soluble) Na (Soluble) Cl HCO3 CO3 B (Soluble) SAR Zn (Soluble) Cu (Soluble)

SAMPLE # DESC[ SOP 815 ]mmhos/cm

[ SOP 805 ] [ SOP 835 ]meq/L

[ SOP 835 ]meq/L

[ SOP 835 ]meq/L

[ SOP 825 ]meq/L

[ SOP 820 ]meq/L

[ SOP 820 ]meq/L

[ SOP 835 ]ppm

[ SOP 840 ] [ SOP 835 ]ppm

[ SOP 835 ]ppm

1A 24-Oct-01 2.12 8.0 10.0 7.2 6.6 8.3 3.3 0.1 0.1 2 <0.02 <0.02 1B 2.09 8.0 9.8 7.0 6.6 8.4 3.3 0.1 0.1 2 <0.02 <0.02

2A 18-May-02 3.28 8.0 14.7 14.5 9.5 13.6 3.8 <0.1 0.1 2 <0.02 <0.02 2B 3.17 8.0 14.6 14.4 9.6 13.4 3.8 <0.1 0.1 3 <0.02 <0.02

Method Detection Limit: 0.01 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 1 0.02 0.02Blank Concentration: - - 0.0 0.0 0.0 0.0 0.0 0.0 0.0 - 0.00 0.00Standard Ref as Tested: 0.29 6.4 0.4 0.7 1.8 0.4 2.1 - 0.3 3 50 8.6Standard Ref Acceptable: 0.29±0.04 6.5±0.4 0.4±0.2 0.8±0.2 1.7±0.2 0.3±0.2 2.3±0.4 - 0.4±0.2 2±2 50±6 8.7±1.2Standard Reference: UCD 005 UCD 004 UCD 005 UCD 005 UCD 005 UCD 005 UCD 005 - UCD 005 UCD 005 UCD 155 UCD 155

Checked and Approved: {electronically signed by E. Sue Littlefield} E. Sue Littlefield, Lab Supervisor

Typical Soil Water Analysis for Well Water San Diego County

Total Chlorides Range Measured in 2006: 8 to 13 mM, 300 – 560 ppm(1 meq Cl x 35 = ppm)

Measurement Water Infiltration Rates:

The Double Ring Infiltrometer

USDA Soil Quality Test Kit

Water holding capacity as affected by soil texture

Leaching Fraction

LR = ECiw5*ECts - ECiw

For ECts 0.67 for avocado and EC 1 irrigation water

1.05*0.67 - 1LR = = .42

ECts = EC threshold sensitivityECiw = EC irrigation water Rhoades 1974

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Toro CnyDusaDuke 7MexicanThomas

Soil Chloride (mg / kg)

Leaf

Chl

orid

e (%

)

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Soil Chloride (mg / kg)

Leaf

Chl

orid

e (%

)Predicted leaf chloride contents of Hass scions grafted on to five different rootstocks. The ANN model parameters are fixed for soil ECe = 4.0 dS/m; water EC 0.8 dS/m; soil pH7; Clay 30%. The dashed bar indicates 0.25% leaf chloride content at which leaf burn symptoms appear.

ANN model output illustrating the inverse relationship between irrigation water salinity and chloride concentrations on accumulation of chloride in leaves of Hass on Toro Canyon rootstock. Fixed model values were pH 7, 35% Clay, soil ECe 2.0, and soil Cl at 4 mg/kg

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WaterEC dS / m

Water Chloride (mg / L)

Leaf

chl

orid

e (%

)

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Water Chloride (mg / L)

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chl

orid

e (%

)

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Water Chloride (mg / L)

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chl

orid

e (%

) EC 0.2

EC 1.2

Application of Artificial Neural Networks for Examining Relationships of Plant, Soil, and Water Variables Affecting Avocado Yields

pH% clay

salinity chlorideyield

ANN Predictive Modeling of Soil and Water Factors on Avocado Leaf Chloride Content, Root Growth and Yields

Input data

Model error

Model Training

Data fit

Due to nutrient interactions that affect yield, scatter plots show no apparent relationship between chloride toxicity and fruit yields.

Root length7.55 mg/kg soil

Slide baradjustment

Variable Value Predicted output variable value

Root length7.55 mg/kg soil

Slide baradjustment

Variable Value Predicted output variable value

ANN Model Output and Sensitivity Analysis of Soil and Water Factors Affecting Root Length

Salinity Calculations for Soil At Different Moisture Levels

Soil Status Water Content CentiBars EC

Saturation 50% 0 1Field Capacity 25% 3 2Air dry 10% 40 5Wilting point <5% >100 10

Irrigation water EC = 1Assume no prior accumulation, Then as soil dries:

Irrigation System Efficiency

Determining the amount of water to actually apply through the irrigation system is done by dividing the amount of water required to replenish the soil reservoir by the efficiency of the irrigation system.

Water that runs off or percolates below the root zone due to nonuniformity of the irrigation system does not contribute to the soil reservoir.

For example, if 30 percent of the water applied runs off the field or percolate below the root zone, the irrigation efficiency is 70 percent and the required applied water for the irrigation would be: 2.50 inches / 0.70 = 3.57 inches

Improving Soil Physical Properties: Bulk Density

Prepare new plantings with mounded rows,include compost or other organic matter

Mulch applications

Gypsum applications in clay soils

Charcoal amendments (Biochar)