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Evapotranspiration, Drought, and Monitoring Plant and Soil Status to Determine Irrigation Scheduling David Bryla USDA-ARS Horticultural Crops Research Unit Corvallis, Oregon Water stress develops quickly in many fruit and vegetable crops

Under-irrigated plants • reduced photosynthesis • less growth • lower yields & poor quality

Drought Drought Many fruit and vegetable crops are also very sensitive to over irrigation

Over-irrigated plants • reduced root function • soil erosion & nutrient leaching • diseases

Flooding Flooding Developing accurate irrigation regimes requires knowledge of both time and amount of water needed to replenish any lost by crop transpiration (water use) and soil evaporation

Transpiration

Weather Irrigation

Rainfall Evaporation Runoff

Subsurface Subsurface flow flow in out Root zone

Deep Capillary percolation rise  Plant water relations and drought

 Estimating crop water requirements

 Irrigation scheduling . Weather-based . Soil-based . Plant-based Water use Growth Productivity

Plant water status (plant water potential)

Measured in units of bars or megapascals (MPa) Components of Water Potential

Plant water Well-watered plant potential

• Low solute concentration • High pressure Water-stressed plant

Turgid cell • Higher solute (high water potential) concentration • Zero pressure

Flaccid cell (low water potential) Soil-Plant-Atmosphere Continuum

Low water potential (atmosphere) -10 to 100 MPa

Stomate Medium water potential (plant) -0.5 MPa

High water potential (moist soil) -0.1 MPa Pressure Chamber / “Pressure Bomb” How it works

Water appears on cut surface

http://pmsinstrument.com Daily changes in water potential in the soil-plant- atmosphere continuum

0.0

Root ) Soil

-0.5 MPa

-1.0 Leaf

Water potential (MPa) Water potential ( potential Water Onset of leaf wilting -1.5

1 2 3 4 5 6 7 DaysTime, days without without water water Slayter (1967) Examining the relationship between plant water potential and the onset of drought Impacts of Drought on Plant Water Use 'Elliott' 'Elliott'

0.0 70

) Predawn Irrigated

-0.5 60 MPa

)

-1 50 -1.0 Midday 40 -1.5 Non-irrigated 30

Transpiration (ml h Transpiration

-2.0 Transpiration (mL/h) Transpiration Leaf water potential (MPa) potential water Leaf Onset of leaf wilting

Plant Plant water potential ( 20 -2.5 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8

DaysTime, without days without waterwater DaysTime, withoutdays without waterwater

Stomata Porometer

) 1

- 300 s

)

-1

2 'Duke' - s 'Bluecrop'

-2 m 250 'Elliott'

mmol 200

150

100

Stomatal conductance (mmol m (mmol conductance Stomatal 0

Stomatal Stomatal conductance ( -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 PlantLeaf water potential potential (MPa) (MPa ) Bryla and Strik (2006) In many fruit and vegetable crops, water stress develops within 3-7 days without rain or irrigation

• Weather conditions

• Plant age • Phenological development

• Cultural practices • Soil texture Water stress level Plant process Mild Severe

Reduced shoot growth

Increased root growth

Reduced water use

Reduced photosynthesis

Leaf wilting

Leaf death/senescence Leaf gowth and internode length are reduced by mild water deficits Leaves wilting is an indication of severe drought Permanent drought damage

Drought Recovery

) 1 - 0.25 1200

s Bluecrop Bluecrop

2 -

)

-1 m

s 1000 -2 0.20 Irrigated IrrigatedIrrigated

Irrigated ) mol

-1 800 0.15

600 Re-wateredRe-watered

0.10 Non-irrigated 400 Non-

ReRe-watered-watered day (g Transpiration irrigated 0.05 Non-irrigatedNon- Transpiration (mL/day) Transpiration 200

Stomatal conducatnce (mmol m irrigated

Stomatal Stomatal conductance ( 0.00 0 0 2 4 6 8 10 12 14 16 18 20 0 2 4 6 8 10 12 14 16 18 20 TimeTime (days) (days) TimeTime (days) (days) Recovery was slow (7-9 days)

Améglio et al. (2000) Drought Causes Embolisms in the Xylem Vessels

'Bluecrop' 100 100% (%)conductance hydraulicofLoss

blocked of Loss (%) hydraulicconductance 80 VulnerabilityVulnerability curve curve

50% blocked 20

0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 AppliedApplied pressure (MPa) (MPa)

Améglio et al. (2000) Embolisms During Actual Water Stress

'Bluecrop'

100

Loss of hydraulic conductance (%)conductance hydraulicofLoss Loss of Loss (%) hydraulicconductance 80 VulnerabilityVulnerability curve curve

InIn situ situ measurementsmeasurements 20

0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 AppliedLeaf water pressure potential (MPa) (MPa)

Améglio et al. (2000) Estimating Crop Water Requirements What is Evapotranspiration?

Nearly all water taken up by a plant is lost by transpiration Transpiration 1 Weather

2 Plant age 3 Cultivar Evaporation 4 Cultural practices

5 Soil conditions Calculating Crop Evapotranspiration

Potential evapotranspiration Climate (ETo)

Penman- Monteith + equation = 900 0.408∆(Rn - G) + √ u2 (es-ea) Net radiation (Rn) T + 273 Soil heat flux (G) ETo = ∆ + √ (1 + 0.34u ) Air temperature (T) 2 Crop Wind speed (u2) Saturated VPD (es-ea) evapotranspiration Slope vapor pressure curve (∆) (ET ) Psychrometer constant (√) c

ETo x Crop coefficient (Kc) = Irrigation scheduling Calculating Crop Evapotranspiration Potential evapotranspiration Climate (ETo) Penman- Monteith + equation = 900 0.408∆(Rn - G) + √ u2 (es-ea) Net radiation (Rn) T + 273 Soil heat flux (G) ETo = ∆ + √ (1 + 0.34u ) Air temperature (T) 2 Crop Wind speed (u2) Saturated VPD (es-ea) evapotranspiration Slope vapor pressure curve (∆) (ET ) Psychrometer constant (√) c

ETo x Crop coefficient (Kc) = Irrigation scheduling Agricultural Weather Station

Potential

evapotranspiration (ETo) Water and Atmospheric Resource Monitoring (WARM) Program http://www.sws.uiuc.edu/warm/weather/

9 Springfield

7 Precipitation Potential ET 6

(inches/month) 3

Rain / evapotranspiration / Rain 2

0 Jan. Feb. Mar. Apr. May Jun. Jul Aug. Sep. Oct. Nov. Dec. 2016 Converting Potential ET to Crop ET Calculating Crop Evapotranspiration Potential evapotranspiration Climate (ETo) Penman- Monteith + equation = 900 0.408∆(Rn - G) + √ u2 (es-ea) Net radiation (Rn) T + 273 Soil heat flux (G) ETo = ∆ + √ (1 + 0.34u ) Air temperature (T) 2 Crop Wind speed (u2) Saturated VPD (es-ea) evapotranspiration Slope vapor pressure curve (∆) (ET ) Psychrometer constant (√) c

ETo x Crop coefficient (Kc) = Irrigation scheduling Calculating Crop Evapotranspiration Potential evapotranspiration Climate (ETo) Penman- Monteith + equation = 900 0.408∆(Rn - G) + √ u2 (es-ea) Net radiation (Rn) T + 273 Soil heat flux (G) ETo = ∆ + √ (1 + 0.34u2) Air temperature (T) Crop Wind speed (u2) Saturated VPD (es-ea) evapotranspiration Slope vapor pressure curve (∆) (ET ) Psychrometer constant (√) c

ETo x Crop coefficient (Kc) = Irrigation scheduling

Developing crop coefficients Precision weighing lysimeter

Entry Crop

Drip tubing

Soil tank

Ladder

Datalogger

Weigh bridge Counter weight Irrigation tank

Precision Weighing Lysimeter

Broccoli Weighing Lysimeter

Bell pepper

ETcrop

Broccoli Daily Water Use by Broccoli

0.5 9/28/02 9/29/02 0.4

Sunny 0.3 Partly sunny

(mm)

crop 0.2

0.1

0.0 00:00 04:00 08:00 12:00 16:00 20:00 00:00 04:00 08:00 12:00 16:00 20:00 Time (hour) Time (hour) Potential evapotranspiration

(ETo)

Weather station Grass lysimeter

Tall fescue (reference crop) Lysimeter

CIMIS weather station Evaporation pan Comparison of Daily Water Use by Broccoli and Grass

0.7 9/28/02 9/29/02 0.6 Crop ReferenceGrass 0.5 Sunny 0.4 Partly sunny

0.3

ET (mm) ET

0.2

0.1

0.0 00:00 04:00 08:00 12:00 16:00 20:00 00:00 04:00 08:00 12:00 16:00 20:00 Time (hour) Time (hour) Calculating Seasonal Crop Coefficients

Kc = ETc/ETo

 ETc = Crop evapotranspiration  From crop lysimeter

 ETo = Potential evapotranspiration  From weather station or grass lysimeter

 Kc = Crop Coefficient Seasonal Kc Curve for Broccoli

1.4 K 1.2 c mid

1.0

0.8

0.6

Crop coefficient 0.4 Kc ini

0.2

0.0 0 10 20 30 40 50 60 70 80 Days after planting Lysimeter

Kc mid

LettuceCrop vs.ETc Referencevs. CIMIS ETo ET 1

0.9

0.8 Lysimeter ET Cimis ETo 0.7

0.6

0.5

0.4 Hourly ET (mm) ET Hourly 0.3

0.2

0.1

0 270 271 272 273 274 275 276 277 278 279 280 Day of Year 12

ET Bell Pepper c Harvest 10 ETo

)

-1

Evapotranspiration (mm·d Evapotranspiration

0 0 20 40 60 80 100 120 Days after planting 30

20 Irrigation Precipitation 10

Sprinkler irrigation

& precipitation (mm) 0 Bell pepper Harvest 1.2

Kc 1.0 1.0

K Ground cover fraction, fraction, cover Ground 0.8 0.8

0.6 0.6

Crop coefficient, fc

0.4 0.4 f 0.2 0.2 c

Kcb ini Kcb dev Kcb mid 0.0 0.0 0 20 40 60 80 100 120 Days after planting by Richard G. Allen Utah State University Logan, Utah, USA Luis S. Pereira Instituto Superior de Agronomia Lisbon, Portugal Dirk Raes Katholieke Universiteit Leuven Leuven, Belgium Martin Smith Water Resources, Development and Management Service FAO FAO - Food and Agriculture Organization of the United Nations Rome, 1998 Irrigation is Scheduled to Replace Crop ET Not Met by Rain

Crop ET estimates are for mature, healthy, well-irrigated plants

9 Springfield

7 Precipitation Potential ET 6

(inches/month) 3

Rain / evapotranspiration / Rain 2

0 Jan. Feb. Mar. Apr. May Jun. Jul Aug. Sep. Oct. Nov. Dec. 2016 Adjustments to crop ET are needed when plants are young or stressed (e.g., nutrient deficient)

1. Under these circumstances, reduce irrigation, but pay close attention to soil moisture

3. There are many devices available to monitor soil moisture (some more accurate than others) 2. Soil moisture monitors should – must be calibrated be installed within the root zone (usually 0.5-3 ft. deep) Irrigation scheduling

Best technique/technology is a function of:

• Irrigation water supply • technical abilities of the irrigator Many technologies are • irrigation system • crop value available for scheduling • crop response to irrigation automatically irrigation • cost of implementing the technology • personal preference

Goal: apply the correct amount of water at the right time (minimize costs/maximize production) Weather-Based Irrigation Scheduling Smartphone App

Download from AgWeatherNet http://weather.wsu.edi/is/ Adjust for Application Efficiency

Sprinklers Microsprays Drip

One line per 20 x 20 ft. spacing, A 6 gph emitter row with 0.5 1.5 gpm sprinkler located between gph emitters heads every other plant every 12 in.

wetting wetting wetting front front front

• irrigated 1-2x’s/week • irrigated 3-7x’s/week • irrigated 3-7x’s/week • efficiency - 35% • efficiency - 68% • efficiency - 90% Due to higher uniformity and efficiency, plants irrigated by drip require only about 25% of the water as those irrigated by sprinklers (even though crop water use is identical)

Daily water requirements for early-season blueberry plants irrigated by sprinklers or drip.

Water requirements (gal./plant/day)z

Irrigation Maximum method May June July Aug. Sept. demand

2.5-ft. spacing Sprinkler 3.9 7.2 9.8 7.0 5.5 13.7 Drip 0.9 1.9 2.5 1.9 1.4 3.6 3-ft. spacing Sprinkler 4.7 8.6 11.8 8.4 6.5 16.5 Drip 1.1 2.2 3.0 2.2 1.7 4.3 4-ft. spacing Sprinkler 6.2 11.5 15.7 11.2 8.7 21.9 Drip 1.5 3.0 4.0 3.0 2.2 5.7 zValues must be adjusted for precipitation before scheduling irrigations. Frequency of Water Applications

• Soil texture (e.g., sand vs. clay) • Irrigation system (e.g., drip vs. sprinkler)

• Rate at which the crop is using water • Overall development of the root system Seasonal Water Demands

Bluecrop 28

26 Low water 24 demands (late spring) 22

20 High water 18 demands (mid summer)

Soil water content (%) 16 Rapidly declining water potential 14 On-set of wilting 12 0 1 2 3 4 5 6 7 8 9 10 Time after irrigation (days) Irrigation System

Frequent water applications are especially important when using drip (restricts soil wetting & produces a smaller root system Root Development 0.0

0.1

0.2

0.3 5-yr-old blueberry plants

Soil depth (m) depth Soil

0.4

0.5 Duke Bluecrop Elliott 0.6 Blueberry is shallow-rooted compared 0 10 20 30 40 50 to many perennial fruit crops Root length density (cm roots/cm-3 soil)

Bryla & Strik (2006) Other methods used to schedule irrigation include soil-based and plant-based approaches

• Relies on soil moisture • Complex monitoring devices • Uses plant growth or • Open & close valves water status measures to automatically determine exactly when • Not universal and water is needed require careful • Most accurate method calibration from site to of irrigation scheduling site • Research done on only • Little research done on a handful of crops high-value crops

Soil-based approach Plant-based approach Why Use a Soil- or Plant-Based Approach?

Microsprays

Soil evaporation

Marketable yield (kg/tree)

Irrigation system Year 3 Year 4 Year 5

Microsprays 7.0 b 13.5 b 26.4 a Surface drip 10.6 a 19.8 a 26.3 a Subsurface drip 9.9 a 20.4 a 26.5 a Peach Lysimeter Example: Using leaf water potential to scheduling irrigation in peach

'Crimson Lady' Peach

0.0 SubsurfaceWell irrigated drip (175% (100% crop ET ET)lys) MicrospraysUnder-irrigated(100% (100% ET croplys) ET) MicrospraysIrrigated by plant-based(plant-based scheduling scheduling) -0.2

-0.4

-0.6

Leaf potentialwater (MPa) -0.8

-1.0 Apr May Jun Jul Aug Sep Oct 2002

Bryla et al., 2005 Irrigation Over the Season

1600

SDI (two laterals, 100% ET ) 1400 Subsurface drip (100% ETc lys) MicrospraysMicrosprinkler(100% (7 day, ET 100%lys) ETc) MicrospraysMicrosprinkler(plant (7 day,-based SWP scheduling)schedule) 1200 29%

1000

800

600

Water applied (mm) 400

200

0 Apr May Jun Jul Aug Sep Oct 2002 Benefits of Plant-Based Scheduling

Crop load Fruit size Yield Treatment (fruit tree-1) (g/fruit) (kg/tree)

Subsurface drip (100% ETlys) 154 178 a 25.1 a

Microsprays (100% ETlys) 152 159 b 19.9 b

Microsprays (plant-based scheduling) 152 179 a 24.9 a Weather-based approach Soil-based approach

Environscan Weather station

Plant-based approaches

Pressure chamber LVDT Transpiration

Weather Irrigation

Rainfall

Evaporation Runoff

Subsurface Subsurface flow flow in out Root zone

Deep percolation Capillary rise Questions?

K = ET /ET Weighing lysimeter c c o Crop Entry

Soil tank

Datalogger Ladder

Weigh bridge Counter Irrigation tank weight