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0 / On-Irrigator Moisture Sensors for Precision Irrigation Ian Woodhead, Adrian Tan, Ian Platt and Sean Richards Lincoln Agritech Ltd., Lincoln University, Christchurch, New Zealand

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1 / PRESENTATION OVERVIEW: 1.Introduction to the moisture sensor How does it enhance an existing variable rate irrigation system? 2.Operating principle How does the sensor measure the microwave reflection of pasture land? 3.Soil moisture content Relationship between sensor measurement and soil moisture 4.Sensor development Sensor prototype and antenna 5.Measurement examples Short lawn grass, medium and long pasture grass, at varying soil moisture 6.Conclusion

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2 / Variable Rate Irrigation Pulsing sprinkler and varying system speed to achieve different application depth. Beneficial for different crops / non-crop areas; soil types; terrain; and obstacles. Need a computer database, knowledge of their effect on water intake, and algorithm. Irrigator needs to know the soil moisture content that are measured at a few locations. Images sourced from ars.usda.gov

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3 / Variable Rate Irrigation Existing variable rate irrigation systems Systems of varying complexities, accounting for water budget, soil type, vegetation, growth stage, dynamics etc. Substantial modeling often required Systems with the ability to communicate and control sprinkler volume or irrigator speed Rely on indicative measurements of soil moisture at small sample size area How does an on-irrigator sensor improve the system? Measures the soil moisture content of the ground area in front of the wetted pattern of an irrigator Measured soil moisture content at meter scale used to modulate the application rate Not entirely based on models/ prior measurements, but real time measurements

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4 / Benefits to the environment and farmer Benefits to the environment Improves soil water dynamics reduces nitrate leaching Benefits to the farmer Correct application of irrigation improves nutrient availability and crop yield, and thus farm productivity. Improved feed quality and uniformity of dairy pasture enhances amount and consistency of milk production Lowers risk of water logging due to excessive water supply in areas of poor drainage More efficient utilization of water and energy lowers the cost of farming Ref: K.C. Cameron et. al., Ann. Appl. Biol., vol. 163, pp. 145- 173, 2013.

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5 / How does the sensor work? Microwave sensor mounted on the boom Soil moisture in front is measured as the irrigator moves Sprinklers application rate is modulated accordingly Soil moisture Ground location

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6 / Sensors Operating Principle Transmitted signal: Time Received signal:

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7 / Sensors Operating Principle Transmitted signal: Time Received signal:

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8 / Sensors Operating Principle Transmitted signal: Time Received signal: Ground backscatter

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9 / Sensors Operating Principle Transmitted signal: Time Received signal: Ground backscatter

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10 / Sensors Operating Principle Transmitted signal: Time Received signal: Ground backscatter

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11 / Sensors Operating Principle Transmitted signal: Time Received signal: Ground backscatter

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12 / Sensors Operating Principle Transmitted signal: Time Received signal: Ground backscatter

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13 / Sensors Operating Principle Transmitted signal: Time Received signal:

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14 / -0.5 m Sensors Theory and Modelling

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15 / -0.4 m Sensors Theory and Modelling

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16 / -0.3 m Sensors Theory and Modelling

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17 / -0.2 m Sensors Theory and Modelling

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18 / -0.1 m Sensors Theory and Modelling

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19 / 0.0 m Sensors Theory and Modelling

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20 / 0.1 m Sensors Theory and Modelling

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21 / 0.2 m Sensors Theory and Modelling

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22 / 0.3 m Sensors Theory and Modelling

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23 / 0.4 m Sensors Theory and Modelling

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24 / 0.5 m Sensors Theory and Modelling

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25 / 0.6 m Sensors Theory and Modelling

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26 / 0.7 m Sensors Theory and Modelling

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27 / Estimating soil moisture Extensive research has been conducted in empirical models of relating soils electrical properties with its moisture content. First order estimate of soil moisture content can be obtained directly due to dominating effects of water on electrical properties Ref: G.C. Topp, J.L. Davis and A.P. Annan, Water Resources Research, vol. 16, no. 3, pages 574-582, June 1980 Accounting for pasture grass effect Method of calibrating the radar scattered signal to account for various crop types has been developed. Crops include corn, soybeans, milo and wheat at various stages of growth. Pasture grass is much shorter than crops, long grass might require minimal compensation. Ref: F.T. Ulaby, A. Aslam, M.C. Dobson, IEEE Trans. AP, 22(2) March 1974, and IEEE Trans. GRS, 20(4), Oct 1982

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28 / Sensor Prototype Sensor on mobile cart with supporting structure for operation in windy conditions Antenna height = 2.7m, pointing at 45 at ground in front Antenna is an array of log periodic dipoles: - Bandwidth = 400 1300 MHz - Gain = 11 dBi - 3-dB beamwidths = 45 7 Agilent Fieldfox vector network analyzer PC for data collection, signal processing and display

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29 / Sensors Antenna Design Array of 4 log-periodic dipole arrays and a wideband 1-to-4 power combiner. ~50 individual antennas in 0.4m x 0.4m x 0.5m volume Still a prototype, to be optimized in size. Proposed method of small area illumination by the sensors antenna Measured footprint of the antenna on ground. Area = 0.62 m 2

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30 / Measurement #1: Lawn grass 20 15 10 5 0 0 24 6 8 1214 16 18 Distance (m) Volumetric Moisture Content (%) Lawn grass, height = 2 cm to 5 cm Volumetric moisture content between 5% to 15% Validation with HS2 Hydrosense probe Lawn grass behind the RFH building at Lincoln University

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31 / Measurement #2: Dry pasture grass Pasture grass, height = 8 cm to 15 cm Volumetric moisture content of soil between 15% to 25% Validation with HS2 Hydrosense probe at 12 cm (blue line) and 20 cm (black line) Pasture grass at Iverson Fields I9, Lincoln University 20 10 0 56 7 8 Distance (m) Volumetric Moisture Content (%) 40 30 50 60 9

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32 / Measurement #3: Wet pasture grass Pasture grass, height = 5 cm to 10 cm Volumetric moisture content of soil between 30% to 40% Validation with HS2 Hydrosense probe at 12 cm (blue line) and 20 cm (black line) Pasture grass at Iverson Fields I9, Lincoln University 20 10 0 56 7 8 Distance (m) Volumetric Moisture Content (%) 40 30 50 60 9

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33 / CONCLUSION Existing Variable Rate Irrigation System Modelling Software Modelling Software VRI Control System Terrain: Digital elevation model Soil Type: Available water holding capacity Obstacles: User excluded areas Crop intake: Crop type, growth stage Soil Moisture: Measurements at few selected locations Soil Moisture: Real time, meter scale measurement in front of irrigator Soil Moisture: Real time, meter scale measurement in front of irrigator Proposed

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34 / CONCLUSION On-irrigator moisture sensor can enhance precision irrigation by providing meter scale soil moisture mapping Development effort shows the feasibility, and limitations of such systems Measured soil moisture from a single sensor controlling the sprinkler water volume provides 1 st level benefit There can be multiple sensors controlling the individual sprinklers to achieve the best water savings Cost savings can be achieved by multiplexing many (low cost) antennas with one single active element.

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