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Evapotranspiration, Drought, and Monitoring Plant and Soil Status To 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 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 50 Stomatal conductance (mmol m (mmol conductance Stomatal 0 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% Loss of hydraulic conductance (%) blocked conductancehydraulic (%) Loss of 80 VulnerabilityVulnerability curve curve 60 40 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 Loss of hydraulic conductance (%) Loss of hydraulic conductancehydraulic (%) Loss of 80 VulnerabilityVulnerability curve curve 60 40 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 8 7 Precipitation Potential ET 6 5 4 (inches/month) 3 Rain / evapotranspiration / Rain 2 1 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 ET 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)Hourly ET 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 8 6 4 Evapotranspiration (mm·d Evapotranspiration 2 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 c K Ground cover fraction, 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 9 Springfield Not Met by Rain 8 7 Precipitation Potential ET 6 5 Crop ET estimates are for mature, healthy,4 well-irrigated plants (inches/month) 3 Rain / evapotranspiration / Rain 2 1 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.
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