Irrigation. Presentation to. 14 January 2009, Amarillo, Texas Steve Evett

Transcription

1 Soil Water Management for Irrigation Presentation to High Plains Irrigation Conference 14 January 2009, Amarillo, Texas Steve Evett

2 Determine The Irrigation Problem When to irrigate, Where to irrigate, How much to irrigate Goals include Avoiding unnecessary yield/quality losses Preventing deep percolation loss of water and nutrients Attaining greatest sustainable profit Yield (quantity & quality) vs. input cost calculation

3 Soil Water Based Scheduling Feel and Appearance Labor intensive, not accurate Gravimetric sampling Accurate, but too laborious and slow Neutron probe, ca 1960 to present Works well, but labor intensive Electromagnetic sensors (since 1980) Can be left unattended Can be wireless Don t work well in most soils Resistance sensors GMS, gypsum blocks

4 3 ) Wate er Co onten (ft 3 ft -3 1 MANAGEMENT - ALLOWED 0.8 DEPLETION 0.6 clay loam Fairly narrow range of water contents: e.g to SATURATION FIELD CAPACITY MAD REFILL POINT, MAD PERMANENT WILTING POINT 0

5 Soil Water Sensor Types Electromagnetic (EM) sensors examples Capacitance sensors Measure resonant frequency of RCL circuit with soil in fringing field of a capacitive element Reflectometers Measure time for reflected voltage pulse to reach a given value typically use a voltage comparator Conventional time domain reflectometry (TDR) Measure travel time of a voltage pulse in rods surrounded by soil

6 EM Technologies Time Domain Conventional TDR Frequency Domain Capacitance sensors Wave Guides Antennas Mixed Technologies Quasi TDR, reflectometers Access tube Electrode Electrode

7 Capacitance sensors - examples Sentek EnviroSCAN and Diviner 2000 (EarthTec) Delta-T PR2/6 and ThetaProbe Adcon C-Probe (AquaSpy) Troxler Sentry 200AP Gopher Aquaterr 200 Decagon ECHO

8 Capacitance sensors pros & cons Capacitance sensors - advantages Relatively inexpensive per unit Most can be datalogged/unattended Some are equipped with wireless all could be Easy to use Disadvantages Sensitive to placement in field Affected by clay content, EC, temperature Are too inaccurate for irrigation scheduling even with field calibration.

9 Capacitance Sensor Problems C D

10 Capacitance Sensor Problems Depth dependent bias Calibration is site specific

11 Capacitance Sensor Problems Method and calibration Wet site Dry site ΔS Difference from DM ΔS mm (25 mm = 1 in) in top meter (40 inches) NMM Direct Measure (DM) 347 (24.7) 173 (10.8) 174 NMM factory 333 (10.7) 198 (10.8) NMM soil-specific 349 (14.6) 173 (13.5) Sentek DM 348 (20.2) 182 (5.0) 166 EnviroSCAN factory 494 (44.8) 258 (38.0) EnviroSCAN soil-specific 330 (23.6) 191 (4.4) Diviner 2000 factory 494 (50.3) 241 (8.6) Diviner 2000 soil-specific 330 (21.8) 187 (7.2) PR2/6 DM 340 (10.2) 180 (2.9) 160 PR2/6 factory calibration 453 (34.8) 239 (29.0) PR2/6 soil-specific 332 (17.3) 190 (11.2) DM is soil water content directly measured using volumetric samples.

12 Spatial noise 2003, Winter wheat, Bushland, TX ve differ rence in storage Mea an relati NMM EnviroSCAN Grav m 3 m m 3 m -3 Trime 75 cm 3 Divineriner 250 cm cm 3 PR1/6 Relative rank

13 2005, fallow, Bushland, TX Water content was equal in the two plots shown here relative differen nce in sto orage Gravimetric NMM Mean EnviroSCAN Trime Relative rank EM sensors showed variability that did not exist

14 N = u α / d 2 S 2 α = u α/2 = d (cm) = S N N Trime Irrigated Dryland Diviner Irrigated Dryland EnviroSCAN Irrigated Dryland Delta-T Irrigated Dryland Sentry 200AP Overall Gravimetric Irrigated Dryland NMM Irrigated Dryland

15 Measurement Volume EnviroSCAN Probe Design Red lines denote axial and radial volume sensed Paltineanu and Starr 1997 Paltineanu and Starr, 1997 Evett et al., 2002

16 Reflectometers - examples CSI CS616 water content reflectometer IMKO Trime T3 Aquatel ESI GroPoint Aquaflex Spectrum TDR300

17 Related to the Time domain reflectometry method Reflection slope is affected by: Rise time of pulse, Soil electrical l conductivity, Bound water (clay surface area and content) t1.bis t1 Travel time is proportional to water content t2

18 BEC and t t increase with θ v Depth θ v PULLMAN CLAY LOAM (cm) 2 v σ a ds/m

19 Reflectometer method End of conductor Wrong travel time Threshold voltage Base voltage t 3 ΔV True travel time t 1 2 Δt err t 2 ΔV/ Δt err decreases as σ a increases Δt err increases as σ a increases

20 Reflectometer Problems Advantages Some are inexpensive, easy to use, can be wireless Disadvantages Do not find true travel time of pulse Interference from Clay content and type Salinity Temperature Temperature Inaccurate in clayey or saline soils

21 (m 3 m 3 ) CS616 wa ater contents cm data y = 0.698x x r² = TDR water contents (m 3 m 3 )

22 How important is σ a interference? Clay soils formed in semi-arid and arid environments, e.g., Pullman and other High Plains soils (Rhoades et al., Handbook 60) Shrink-swell clays Irrigated lands Shallow water tables Brackish waters

23 Example: pe Drip irrigation in California End of July to middle of August

24 TDR vs. Not TDR TDR systems - examples CSI TDR100 based system SoilMoisture Trace system Dynamax Vadose TDR system Not TDR Spectrum TDR300 ESI GroPoint Aquaflex Aquatel CSI CS616, 625, etc.

25 SWAT Committee Coalition of irrigation manufacturers Landscape irrigation focus Sponsored by IA Supported by EPA Climate-based smart controllers Soil moisture sensor-based smart controllers Limited testing protocol

26 AquaSpy New on the Market Based on C-Probe sensor Technology similar to EnviroScan EarthTec Sensors from Sentek Pty, Australia Technology is EnviroSCAN and Diviner 2000 Both: Are capacitance sensors in access tubes Share problems of inaccuracy and spatial variabilty

27 Direct Observation Methods T handle of same material Push-probe, shovel insertion, etc. Fairly accurate for depth of wetting front important for assessing irrigation uniformity, deep percolation Inaccurate for water content, but useful in experienced hands 5 ft Approx. 9/16-inch steel rod Approx. 1/2 inch ball bearing welded to end

28 Soil Water Potential Sensing Sensors Tensiometers Granular matrix sensors Gypsum blocks Method of use Identify set point for irrigation (start or stop irrigation) Observe often enough to react well

29 Sprinkler-irrigated alfalfa scheduled using GMS sensors. Clinton Schock ( sensors at 25-cm depth. = harvest Too dry Information not much used by irrigator

30 Questions Steve Evett Research Soil Scientist and Lead Scientist Mobile: Irrigation and Crop Water Use Research Team, Conservation & Production Research Laboratory, Bushland, Texas