Soil moisture sensor systems and methods

1. A soil moisture sensor system comprising:

a sensor configured to receive soil between parallel plates;

a capacitive measurement circuit operatively associated with the sensor plates;

said capacitive measurement circuit comprising a stimulus portion and an analysis portion;

said stimulus portion generating a reference signal;

said analysis portion measuring the response from the sensor plates with respect to the reference signal in separate imaginary and real component measurements; and

using the response components measurements to compute a capacitance of the sensor plates based on known sensor plate geometry to derive a moisture measurement, wherein the known sensor plate geometry includes L as the length of the sensor, H as the height of the sensor, and d as the separation between the sensor plates and wherein moisture content of the soil is based on the following relationship: C=(LH/d)ε 0 ε r .

2. The system of claim 1 wherein the sensor is configured for positioning at root level.

3. The system of claim 1 wherein the capacitive measurement circuit is stimulated with a digital to analog converter (DAC) whose output is stepped through the values of a sin wave.

4. The system of claim 1 wherein capacitor geometry does not influence the sensor.

5. The system of claim 4 wherein the capacitor geometry is known and remains constant.

6. The system of claim 1 further comprising a drainage mechanism for the soil between the sensor plates.

7. The system of claim 1 wherein an area between the sensor plates is readily filled with soil.

8. The system of claim 1 wherein the sensor plates are arranged parallel to one another.

9. The system of claim 1 wherein the imaginary component measurement is reactive and the real component measurement is resistive.

10. A method of determining soil moisture content comprising:

receiving soil between at least two plates;

measuring capacitance of the soil using a capacitive measurement circuit operatively associated with the sensor plates;

generating a reference signal from a stimulus portion of said circuit;

measuring the response from the sensor plates with respect to the reference signal in separate imaginary and real component measurements; and

using the response component measurements to compute a capacitance of the sensor plates based on known sensor plate geometry to derive a moisture measurement, wherein the known sensor plate geometry includes L as the length of the sensor, H as the height of the sensor, and d as the separation between the at least two plates, and wherein moisture content of the soil is based on the following relationship: C=(LH/d)ε 0 ε r .

11. The method of claim 10 wherein the sensor plates are arranged parallel to one another.

12. The method of claim 11 further comprising stimulating the capacitive measurement circuit by stepping output from a digital to analog converter (DAC) through a sin wave.

13. The method of claim 10 further comprising calibrating the sensor for temperature.

14. The method of claim 10 further comprising calibrating the sensor for a physical configuration of the plates.

15. The method of claim 14 wherein calibrating the sensor includes:

measuring the permittivity in air; using the permittivity in air as a correction factor;

determining a corrected soil moisture measurement by dividing an actual measurement of the sensor by the permittivity in air.

16. The method of claim 15 wherein calibrating the sensor further comprises storing the permittivity in air measurement for use with future measurements by the sensor.

17. A system for determining moisture content in soil comprising:

plate means for receiving soil therebetween;

sensor means for measuring capacitance of the soil;

stimulus means for generating a reference signal;

analysis means for measuring the response from the sensor means with respect to the reference signal in separate imaginary and real component measurements; and

computational means for computing the capacitance of the sensor means based on known sensor plate geometry and deriving a moisture measurement, wherein the known sensor plate geometry includes L as the length of the plate means, H as the height of the plate means, and d as the separation between at least two plates of the sensor means, and wherein moisture content of the soil is based on the following relationship: C=(LH/d)ε 0 ε r .

18. The system of claim 17 further comprising means for calibrating the sensor means for temperature.

19. The system of claim 17 further comprising means for calibrating the sensor means for separation of the plate means.