Low Tech, Low Cost Soil moisture Monitoring and Interpretation

Transcription

1 Low Tech, Low Cost Soil moisture Monitoring and Interpretation Michael Cahn Water Resources and Irrigation Advisor UC Cooperative Extension Monterey, San Benito, and Santa Cruz Counties UC Monterey Co 1432 Abbott St. Salinas CA (831)

2 Main reasons for monitoring soil moisture: Troubleshooting irrigation problems (uniformity) Assist with irrigation scheduling

3 My most trusted tools for irrigation scheduling: Flow meter CIMIS weather data Excel spreadsheet Watermark soil moisture sensor

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7 Weather based Irrigation Scheduling CIMIS weather network Daily Evapotranspiration (inches/day) /1 2/1 3/1 4/1 5/1 6/1 7/1 8/1 9/1 10/1 11/1 12/1 Date Pajaro Freedom Morgan Hill

8 Welcome Back MIKE My Reports My Station Lists My Preferences Account Management Log Off Edit Registration Change Password My Reports The My Reports allows you to perform single-click reporting, select report preferences, and prepare custom reports. There are three station lists (List 1, List 2, and List 3) and each list can hold up to a maximum of 10 stations. A list must contain at least one station before executing reports from this page. You can add and remove station(s) from the list by clicking on Create/Change Station Lists and clicking on Remove. Once a list has been created, clicking on a station number will provide detailed information about the station. After specifying Station Lists, you can generate a report in any one of the report options listed under Quick Reports by clicking on the list number to the right (list 1, list 2, or list 3). These reports are generated using the Preferences listed at the bottom of the Station Lists. Preferences for Quick Reports can be changed by clicking on Change Preferences at the bottom of the Station Lists. Custom reports allows the user to select the options (climatic parameters), to be reported. Quick Reports Report Options Standard Hourly (using prefs) list 1 list 2 list 3 Standard Daily (using prefs) list 1 list 2 list 3 Standard Daily ETo Variance (using prefs) list 1 list 2 list 3 Standard Monthly (using prefs) list 1 list 2 list 3 Standard Monthly Average ETo (using prefs) list 1 list 2 list 3 My Custom Reports Report Options pajaro salinas undefined undefined list 1 list 2 list 3 customize list 1 list 2 list 3 customize customize customize Tip: When specifying the stations for station-lists, group stations by geographic proximity. You can then report by geographic region. Reports based on stations in close proximity can be a useful tool for understanding data patterns in and around the area of interest. My Station Lists List 1 List 2 List My Preferences Name Zip Codes Units Output Hourly Report Daily Report Monthly Report Create/Change Station Lists Value English WEB Report 7 Days 7 Days 12 Months Change Preferences Back to Top About Us Contact Us Site Map Conditions of Use Privacy Policy Comments or Suggestions? 2004 State of California.

9 crop soil evapotranspiration irrigation schedule B C G K L M N O Month Interval Rooting Depth (feet) Canopy Cover (%) Allowable Depletion (in) Reference Crop ET (in/day) Daily Crop ET (in/day) Irrigation Interval (days) Irrigation Time (hours) Irrigation Amount (inches) Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec

10 Soil moisture monitoring to cross-check an irrigation schedule: Volumetric Soil Moisture (%) 20 50% ETc 75% ETc 100% ETc 125% ETc 21 Mar 04 Apr 18 Apr 02 May 16 May 30 May 13 Jun 27 Jun 11 Jul Date

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12 Which Measure of Soil Moisture? Gravimetric: g of water/g of soil, %wt/wt Volumetric: cm3 of water/cm3 of soil, % v/v Tension (Matric Potential): 1 kpa = 1 centibar 0-60 cbar for vegetables/strawberries 1500 cbar = permanent wilting point

13 Soil probe for Gravimetric Moisture

14 Undisturbed Cores for Volumetric Moisture Analysis

15 Tensiometers monitor the matric potential (tension) of the soil Measurement of soil moisture that is most related to water status in a plant

16 Factoring in Soil Water Holding Capacity in Irrigation Scheduling Available Water Holding Capacity for Various Soil Textures Soil Texture Field Capacity (~20 cbar) Wilting Point (1500 cbar) Available Moisture inches of water per foot of soil Sand Loamy Sand Sandy Loarm Loamy Sand Silt Laom Sandy Clay Loam Sandy Clay Loam Clay Loam Silty Clay Loam Silty Clay Clay Problematic for irrigation scheduling of cool season vegetables and berries

17 How accurate do volumetric soil moisture sensors need to be for vegetables and berries?

18 Soil Texture and Bulk Density of 3 soils Particle Size Soil Soil Texture sand silt clay Bulk % g/cc 1 Silty clay Silty clay loam Loam

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20 Volumetric Moisture vs Tension % Volumetric water Soil Moisture Tension (kpa) 10% Sand, 44% Clay 21% Sand, 34 % Clay 46% Sand, 22% Clay

21 Soil Texture, Water Holding Capacity, and Available Moisture Tension 30 kpa Tension 80 kpa Saturated Soil Soil Texture Saturated tension Volumetric Moisture Available Moisture Available Moisture kpa % % inches/foot % inches/foot 1 Silty clay Silty clay loam Loam

22 Is Your Soil Moisture Sensor Sufficiently Accurate? Sensor type moisture units accuracy (+/ ) resolution range Echo probe 20 capacitance volumetric 4% 0.10% 0 40 % Echo 5 capacitance volumetric 3% 0.10% 0 100% theta probe frequency domain volumetric 5% 1.00% 5 60% PR2 capacitance volumetric 6% 0 40%

23 Irrigation scheduling: Frequent repeated measurements in a few locations will provide an accurate sense of relative changes in soil moisture. Soil moisture distribution: Measurements from many locations will provide an accurate snapshot of soil moisture distribution.

24 Principal Categories of Soil Moisture Sensors Hand probe Tensiometer Electrical resistance blocks Neutron probe Dielectric sensors

25 Soil probe + inexpensive + no salinity interference + responsive at high moisture contents - gravimetric moisture - manual use only

26 Appearance of sandy loam and fine sandy loam soils at various soil moisture conditions (NRCS Guidelines) 75 to 100 percent available 0.4 to 0.0 inches per foot depleted Wet, forms a ball with wet outline left on hand, light to medium staining on fingers, makes a weak ribbon between the thumb and forefinger 75 to 100 percent available 0.4 to 0.0 inches per foot depleted Wet, forms a ball with wet outline left on hand, light to medium staining on fingers, makes a weak ribbon between the thumb and forefinger. 50 to 75 percent available 0.9 to 0.3 inches per foot depleted Moist, forms a ball with defined finger marks, very light soil/water staining on fingers, darkened color, will not slick

27 Tensiometer + relatively inexpensive + easy to install and use + can interface with datalogger + no salinity interference + responsive at high moisture contents - limited moisture range (0-70 cbar) - require frequent maintenance - loss of vacuum

28 Granular Matrix Blocks + inexpensive + easy to install and use + low maintenance + can interface with datalogger + range of cbar - slow response time - salinity interference > 2 ds/m

29 Neutron Probe Radioactive source Hydrogen in water absorbs fast neutrons Probe detects emission of slow neutrons +accurate volumetric measurement +not affected by salinity +senses a large volume of soil -initially expensive -readings are time consuming -need a license to own and operate -cannot use with a datalogger

30 Dielectric Sensors: (newest type) Time domain reflectometry (TDR) Frequency domain reflectometry (FDR) Capacitance + potentially accurate volumetric measurement + many configurations + interface with datalogger - relatively expensive - salinity interference - FDR and capacitance sense a small volume - often difficult to install

31 TDR Sensors: Campbell Scientific TDR IMKO Trime Dynamax Vadose TDR Tectronix TDR Gro-Point ESI Aquatel AT210 Spectrum TDR300

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33 FDR/Capacitance Sensors: Netafim flori SDEC HMS 9000 Delta-T theta probe Troxler Sentry 200 AP PRISM CMP Gopher Sentek Diviner Sentec Enviroscan Adcon C-probe Aquaterr 200 Aquaflex

34 PRISM Sentry 200AP Theta-Probe Sentek Diviner C-Probe

35 What seems to work well:

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44 Placement of sensors cost application (scheduling/troubleshooting) irrigation system (drip/sprinklers) rooting depth soil and field characteristics

45 Guidelines for placement of sensors for checking scheduling minimum of 3 locations in field (head, middle, and tail of field) place in plant row 2 depths in root zone

46 Dataloggers

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48 Soil moisture tension at 1 and 2 foot depths in Brussels sprout fields (Drip and Sprinkler Fields) Soil Moisture Tension (cbar) ft Drip Field 2 ft Sprinkler Field /1 8/1 9/1 10/1 11/1 12/1 7/1 8/1 9/1 10/1 11/1 12/1 Date Date Soil Moisture Tension (cbar)

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50 Trouble shooting irrigation problems Under/over irrigating Irrigation frequency not matching crop needs Non-uniformity across field Excessive deep percolation Limited lateral movement of moisture across beds

51 Summary Soil moisture monitoring can help trouble shoot irrigation problems ( uniformity or scheduling) New developments in sensors increase flexibility in soil moisture monitoring: Dielectric sensors offer more options Dataloggers allow for automated collection of data