Blaine Hanson Department of Land, Air and Water Resources University of California, Davis
Irrigation Water Management - Science, Art, or Guess?
Irrigation water management: questions to answer When should irrigations occur? How much water should be applied? How long should the irrigation last?
Avoid Deficit Irrigation
Avoid Overirrigation
Methods ET based (sometimes called the water balance approach) Plant based Soil moisture measurements Experience Guess
ET based method Calculate the crop evapotranspiration (ET) between irrigations and apply that amount plus any needed for irrigation efficiency Assumes that the ET between irrigations equals the soil moisture depletion (does not apply under shallow ground water conditions ET = Kc x ETo x IN ET = crop evapotranspiration Kc = crop coefficient ETo = reference crop ET (California Irrigation Management Information System) IN = days between irrigations
Plant based Use leaf water potential measurements to determine when to irrigation Pressure chamber Time consuming Use ET = Kc x ETo to determine how much water to apply
Soil moisture measurements Approach 1 measure changes in soil moisture content between irrigations assumes that the ET between irrigations equals the soil moisture change between irrigations When to irrigate How much to apply Approach 2 measure soil moisture tension to determine when to irrigate Soil moisture tension tenacity with which water is retained in soil (the drier the soil, the higher the soil moisture tension Use reference crop ET and crop coefficients to estimate the amount of water to apply Not recommended for drip and microsprinkler irrigation
Recommended method for drip and microsprinkler irrigation Select an appropriate irrigation frequency Use the ET based approach to determine how much water to apply Do not use soil moisture measurements to determine how much water to apply Monitor soil moisture to ensure adequate irrigation over time Periodic measurements Limited data May be difficult to identify trends in soil moisture Continuous measurement trends are readily evident in data
Methods for monitoring soil moisture Soil probe Tensiometers soil moisture tension Electrical resistance blocks soil moisture tension Watermark sensor Gypsum block Neutron moisture meter soil moisture Radioactive source licensing, storage Not appropriate for grower use Dielectric moisture sensors soil moisture
Soil probe
0 Tensiometer Cap Reservoir 100 50 Vacuum Gauge Water Porous Ceramic Cup
Electrical Resistance Blocks Watermark Block Gypsum Block
Neutron moisture meter
Dielectric Soil Moisture Sensors Sensors measure an electrical property of soil called the dielectric constant varies with soil moisture content Calibration equation relates dielectric constant to soil moisture content
GroPoint Dielectric Soil Moisture Sensor
Echo Dielectric Soil Moisture Sensor
Enviroscan Dielectric Sensor
Conclusions of USDA ARS Research on dielectric soil moisture sensors All dielectric sensors studied required site specific calibration None of the sensors performed within the accuracy specifications published by the manufacturers Sensors were sensitive to soil bulk electrical conductivity Calibrations of sensors were more difficult to establish than for the neutron probe Sensor readings were sensitive to small scale variations of soil properties due to their very small zone of influence. These small scale variations were smaller than the scale at which plants respond to soil moisture
Drip/microsprinkler irrigation: where should the sensors be installed? Soil moisture under drip/microsprinkler irrigation varies with distance and depth from the emitter Root density also can vary with distance and depth from the emitters Installation too close very wet soil Installation too far little or no response to irrigation
Microsprinkler water application patterns Site 1 (Valencia) 14 16 Site 2 (Young Navel) Distance (feet) 14 12 10 8 6 4 2 Spinner High 110 100 90 80 70 60 50 40 30 20 10 0 Low -10 Distance (feet) 12 10 8 6 4 2 Fanjet High 110 100 90 80 70 60 50 40 30 20 10 0 Low -10 0 0 2 4 6 8 0 0 2 4 6 Distance (feet) Distance (feet) Microsprinkler Microsprinkler
Soil moisture microsprinkler (citrus) Soil water content July 24 (just after irrigation) Depth (feet) Depth (feet) -1-2 -3-1 -2-3 2 3 4 5 6 7 8 9 Distance from micorsprinker (feet) July 29 (just before next irrigation) 2 3 4 5 6 7 8 9 Distance from microsprinkler (feet) 1.7 High 1.6 1.5 1.4 1.3 1.2 1.1 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 Low
Soil moisture drip irrigation -10-20 Depth (inches) -30-40 -50-60 -70 20 30 40 50 60 70 80 90 100 Distance From Tree (inches)
Root pattern flood irrigation of trees Tree Trunk Wetted Area Low Root Density Tree Skirt High Root Density
Root pattern microsprinkler irrigated tree Tree Trunk Wetted Area Low Root Density Tree Skirt High Root Density
Root pattern drip irrigated tree Tree Trunk Wetted Area Low Root Density Tree Skirt High Root Density
Soil moisture tension drip irrigated grapes 100 Grapes Soil moisture tension (centibars) 80 60 40 20 Distance From Drip Line (feet) 2 4 6 0 01-Mar-03 01-May-03 01-Jul-03 01-Sep-03 01-Nov-03 01-Jan-04 Courtesy Blake Sanden, UCCE, Kern County
How frequently should soil moisture be measured periodic vs. continuous measurements Periodic Measurement intervals once or twice per week Appropriate for sprinkle, furrow, and flood irrigation Not recommended for drip or microsprinkler irrigation Continuous Measurement interval few minutes to once per day Recommended for microirrigation
What Do The Readings Mean?
Soil moisture tension flood irrigated walnut 200 Depth (feet) 6 12 18 24 Walnut (flood irrigated) 150 18-Jun 25-Jun 28-Jun 2-Jul 10-Jul 12-Jul 16-Jul 19-Jul 23-Jul 30-Jul 6-Aug 9-Aug 13-Aug 16-Aug 20-Aug 23-Aug 27-Aug 1-Sep 3-Sep 6-Sep 10-Sep 13-Sep 17-Sep 20-Sep 2-Oct 100 50 0 Watermark Block Reading (centibars)
Soil moisture tension microsprinkler irrigated citrus 100 Plot 4-6" 80 60 40 20 0 100 12" 80 60 40 20 0 100 24" 80 60 40 20 0 Tensiometer Readings (centibars) 1-Aug 2-Aug 5-Aug 6-Aug 8-Aug 11-Aug 12-Aug 13-Aug 15-Aug 16-Aug 19-Aug 20-Aug 22-Aug 23-Aug 26-Aug 27-Aug 29-Aug 30-Aug 2-Sep 3-Sep 5-Sep 6-Sep 9-Sep 10-Sep 12-Sep 13-Sep 16-Sep 17-Sep 19-Sep 20-Sep 23-Sep 24-Sep 26-Sep 27-Sep 30-Sep 1-Oct 3-Oct 4-Oct 6-Oct 10-Oct 11-Oct 13-Oct 14-Oct 15-Oct 17-Oct 18-Oct 21-Oct 22-Oct 24-Oct 25-Oct 28-Oct 29-Oct 31-Oct 1-Nov 4-Nov 5-Nov 7-Nov 8-Nov 4-Dec 13-Dec Date Soil moisture tension (centibars)
Continuous monitoring of soil moisture Sensor type Compatible for continuous measurement multiple measurements per day to once per day Placement of sensors (distance, depth) relative to drip emitters/microsprinklers Data logger Computer/software for evaluating data Wireless system or computer download Consultant or grower
Sensors for continuous monitoring of soil moisture Watermark electrical resistance blocks soil moisture tension Dielectric moisture sensors soil moisture
AMD 400 Data Logger
Irrometer Monitor Data Logger
Soil moisture tension drip irrigated almond 160 140 120 100 80 A - Almond - 47.9 inches Depth (inches) 18 36 60 Soil Moisture Tension (centibars) 60 40 20 0 01-Jan-04 01-Mar-04 01-May-04 01-Jul-04 01-Sep-04 01-Nov-04 160 140 B - Almonds - 59.7 inches 120 Depth (inches) 100 80 18 36 60 60 40 Courtesy Blake Sanden, UCCE, Kern County 20 0 01-Jan-04 01-Mar-04 01-May-04 01-Jul-04 01-Sep-04 01-Nov-04
Soil moisture tension flood irrigated peach Soil Moisture Tension (centibars) 200 180 160 140 120 100 80 60 40 20 Peach Orchard - Flood Irrigation Depth (feet) 1 2 3 1 May 1 Jun 1 Jul 1 Aug 1 Sep 0 100 120 140 160 180 200 220 240 260 Day of Year
Wireless Systems Advantage frequent access to data from office Sensors Data logger Transmitter device at logger radio, cell phone Receiver device office, network Computer
Automating the microirrigation system Automation controller turns the irrigation system on and off Devices: soil moisture sensor, data logger, wireless system, controller What triggers the irrigation? Soil moisture level Predetermined amount of evapotranspiration Days between irrigation
anrcatalog.ucdavis.edu