This invention relates to a method and means pertaining to assessment of soil moisture.

The problem to which this invention is directed relates to difficulties in establishing soil moisture which can be reliably used with respect to a variety of different soils and with water that can be sometimes more saline than other waters, and which can establish such moisture content at a selected depth within the soil and all of these by means which are both economic and which can be operated remotely.

There are of course many different techniques presently in existence these including measurement of electrical conductivity which suffers from being substantially responsive to the salinity of the water separate from any total moisture content, and there are finally techniques which use the thermal characteristics of the soil which can to some extent be an indicator of moisture content.

This invention is directed specifically to techniques of moisture content using means to assess thermal properties of the soil.

Previous attempts have been made to use the thermal properties of the soil as an indication of moisture content, but we have found that such previous attempts as have been made have been subject to significant difficulties of which it is the object of this invention to overcome.

According to this invention, there is proposed a method of assessing an extent of moisture content within soil which includes subjecting a part of the soil or an equivalent material in terms of water take up potential to be assessed to a selected heating, and detecting any resultant temperature differentials such that a magnitude which is substantially proportional to a thermal capacitance of the sample is obtained.

Such a technique differs from previous techniques in which the assessment has depended to a very large extent upon thermal conductivity of the soil.

For a number of reasons which will be later explained in detail, it has been found that if techniques are used so that it is substantially soil thermal capacitance which is detected or at least the results have a direct

proportionality to such thermal capacitance rather than thermal conductivity, then a correlation with moisture content is very much better than has hitherto been possible and further more, the results are very much less dependant upon soil type and other varying factors.

In order to isolate the effects of thermal heating due to capacitance rather than conductance, various techniques can be used but one that is preferred is to substantially isolate a selected portion of the soil or its equivalent in respect of water take up characteristics and thermal capacitance from a remainder of the soil having a connection only so that there can be a continuing equilibrium reached of soil held within a sample location with a greater mass of soil in which a detector body is located.

In preference, there is therefore proposed a body providing some insulating in a thermal sense of heat source from a remainder part of the soil with in which the detector is buried, and temperature sensing means within the vicinity of the heat source means are adapted especially to detect a peak temperature reached subsequent to a pulse and then if required, a drop off against time of such temperature of the soil.

In preference, a sample of this soil is contained within a cylindrically shaped aperture open at both ends which is adapted to be inserted within the soil and to have a soil or its equivalent of the type being detected inserted and as appropriate in fact slightly tamped into the aperture space.

The cylindrical shape is preferably of constant cross sectional shape and size along its length and within a centre of the cylindrical shape, a surrounding surface is comprised of a metal of high conductivity such as stainless steel and at a first side there is a heating means comprising an electrical resistor which can be remotely pulsed with an energy level which resistor is in contact with the stainless steel surface so that would be caused to raise its temperature and by transmitting the temperature quickly through the stainless steel surface subject with relatively constant conduction and radiant heating effects, the central portion of the soil within the aperture.

Subsequent to termination of the heating pulse, there are temperature detection means also coupled to the stainless steel conductor and such that the temperature can be remotely determined and in accord with the method,

the peak temperature of the soil subsequent to the heating pulse is detected.

It is found that such a peak temperature reached can be calibrated with reasonably accurate correlation to an expected percentage of moisture within a soil sample and that this provides a consistent assessment over a range of soil types including high silica content and high clay content type soils.

The assessment of thermal capacity can be achieved then by containment in some thermally insulating way of a soil sample or its equivalent which is however kept in appropriate communication with a remainder of the soil but such that loss of heat by thermal conductances is substantially reduced and soil subject to the temperature rise together with means for providing communication from a heating source to the soil, are generally insulated in a thermal sense from a remainder of the soil material.

The concept then differs from a probe in which a metal rod is inserted into soil to be tested and in which there is a heat source and a temperature detector but such that the heat source will heat surrounding soil which is everything but contained and any temperature detection is sufficiently remote from such temperature source such that any detection will be found to be substantially correlated with thermal conductance rather than thermal capacity of the surrounding soil.

One of the more important aspects of the invention relates to the apparatus which can now be inserted into the ground which can be used for this function and accordingly the invention can be said to reside in apparatus for assisting determination of moisture content of soil, the apparatus including a body comprised substantially of a thermally insulating material, an open cavity within the body adapted to hold soil of the type to be tested, an electrically conducting circuit within the body with externally accessible electrical connections including resistance means to provide a source of heat from within the body and into the cavity, and temperature detection means within the body adapt to provide by way of electrical connections remotely accessible information providing information on any detected temperatures subsequent a heating of the soil within the cavity.

In preference, the body is comprised of a cylindrical member constituted by

being formed of a plastics material of thermally insulating character but having therein and defining within a cylindrically shaped central core which is coaxial with the cylindrical shape of the plastics material forming the body.

The method according to the invention can variously reside in the broader concept expressed previously or in the further method of effecting assessment of soil moisture comprising the steps of locating a body which has an open cavity therein for holding and capturing soil, within the soil to be tested, holding some of the soil or its equivalent in such a cavity and such that such holding means allow for a diffusion of moisture from the surrounding soil into any sample thus contained, effecting a selected heating of the soil within the cavity and detecting any resulting peak temperature reached subsequent to such heating.

In preference, such further detection of resulting temperatures comprises detecting the maximum temperature differential achieved by reason of a select given temperature pulse.

Alternatively the invention can be said to reside in a soil moisture probe comprising means for detection of temperature, means to generate heat, a body adapted to substantially encompass a sample of the soil or an equivalent material in terms of water take up potential but allowing communication with the soil external to the body, and means for detecting any resultant temperature differentials such that a magnitude which is substantially proportional to a thermal capacitance of the sample is obtained.

The soil moisture probe in preferance can be further characterised by the means to generate heat provides singularly or repeatedly a pulse of heat of known characteristics of magnitude, change in magnitude with regard to time and duration for an interval of time.

The soil moisture probe in preference can be further characterised by the body providing some insulation in a thermal sense of heat generated by the means to generate heat for the sample from the soil within which the probe is buried but external to the body, and the means for detecting being adapted for the detection of temperature within the vicinity of the means to generate heat especially adapted to detect a peak temperature reached

subsequent to a pulse and then if required, a drop of temperature against time of such temperature of the soil.

The soil moisture probe can, in preference, be further characterised as being a probe in which the body is comprised of a cylindrical member constituted by being formed of a plastics material of thermally insulating character but having therein and defining within a cylindrically shaped central core which is coaxial with the cylindrical shape of the plastics material forming the body.

The soil moisture probe can, in preference, be further characterised as being a probe in which the body is a cylindrically shaped aperture open at both ends which is adapted to be inserted within the soil and to have the sample inserted therein.

The soil moisture probe can, in preference, be further characterised as being a probe in which the sample is slightly tamped into the aperture space.

The soil moisture probe can, in preference, be further characterised as being a probe in which the sample is soil of the type or the equivalent material in terms of water take up potential is an equivalent of soil in which the probe is buried.

The soil moisture probe can, in preference, be further characterised as being a probe in which the means to generate heat is of an electrical resistance heater type.

The soil moisture probe can, in preference, be further characterised as being a probe in which the means for detection of temperature is adapted to assess the thermal capacity of the sample substantially from the peak detected temperature and the thermal conductance substantially from the decay over time of the detected temperature.

Alterntively the invention can be said to reside in a soil moisture probe comprising a body having a partly enclosed space, an electrical resistor with the body appropriate to effect a heating of any material within the partly enclosed space, and temperature detection means adapted to detect the temperature of any material within the partly enclosed space subsequent to any heating from the electrical resistor.

Further to the last paragraph the invention can in preference be characterised by including means to provide an electrical current into the electrical resistor for a selected duration.

Further to the last two paragraphs the invention can in preference be a soil moisture probe wherein the partly enclosed space is a cylindrically shaped chamber open at both ends of the cylindrical shape.

In preference the invention can be further characterised as a soil moisture probe wherein there are means to detect and store a peak temperature of any material within the partly enclosed space.

In preference the invention can be further characterised as a soil moisture probe in which the body is comprised of a thermally conducting material having included therein an electrical resistor, a partly enclosed space within the body adapted to be heated by the electrical resistor, temperature detection means adapted to measure the temperature of any material within the partly enclosed space, and the body of the probe being a substantially cylindrical tube, herein refered to as the first tube, made of a material which is a thermal insulator except for a second cylindrical tube made of metal, the first tube encasing the second tube except for the inner surface of the second tube, and the length to diameter ratio of the first tube being chosen such that the magnitude of the area defined by the apertures of the first tube is small compared with the magnitude of surface area of the inner surface of the tube.

Alternatively the invention can be said to reside in a method of effecting assessment of soil moisture comprising the steps of locating a body which has a enclosed space therein for holding soil within the soil to be tested, holding a sample of some of the soil or an equivalent material in terms of water take up potential in such a space such as to allow for a diffusion of moisture from the surrounding soil into any sample thus contained, effecting a selected heating of the soil within the space and detecting any resulting peak temperature reached subsequent to such heating.

The method of effecting assessment of soil moisture may be further characterised as one where the step of effecting selected heating comprises applying a pulse of electrical current to an electrical heater for a selected interval of time to heat the sample.

The method of effecting assessment of soil moisture may be further characterised as one where the step of effecting selected heating comprises applying singularly or repeatedly a pulse of heat for an interval of time to the sample.

The method of effecting assessment of soil moisture may be further characterised as one in which the step of detecting of temperature provides an intelligible result for the thermal capacity of the sample substantially from the peak detected temperature and the thermal conductance substantially from the decay overtime of the detected temperature.

Alternatively the invention can be described as an apparatus for the control of an irrigation means by the determination of soil moisture content comprising: an electrical power supply; at least one probe adapted to be buried in the soil, incorporating an electrical resistive heater and at least one thermal couple, the probe being connected to the distal power supply by means of at least one wire, and the body of the probe being a substantially cylindrical tube, herein refered to as the first tube, made of a material which is a thermal insulator except for a second cylindrical tube made of metal, the first tube encasing the second tube except for the inner surface of the second tube, and the length to diameter ratio of the first tube being chosen such that the magnitude of the area defined by the apertures of the first tube is small compared with the magnitude of surface area of the inner surface of the tube; a controller incorporating: a microprocessor, a memory means for microprocessor program and data, means to interface the microprocessor with the thermal couple or couples and the power supply; means for setting a setpoint; wire or wires connecting the controller to the power supply and to the distal thermocouple or thermocouples; and the controller being adapted to control the flow of electrical energy from the power supply to the heater or heaters, determine a peak in the signals from the thermocouple or thermocouples, utilise the peak in the signals and

any calibration factors to determine the moisture content of the soil, and inhibit the irrigation means from irrigating if the soil moisture content is sufficient.

EXPLANATION OF DRAWINGS

Figure 1 is graph of calibration curve for a conventional thermal probe in sand. The X-axis is the percentage moisture content, and the Y-axis is Tend, the temperature reading of the probe.

Figure 2 is graph of a typical temperature pulse resultant from a heater being on (8) for a limited period of time. The X-axis is the time in seconds, and the Y-axis is the temperature in degrees C.

Figure 3 is graph of a probe response as a function of conductivity (k) for a constant thermal capacity (Cp=800). The X-axis is the time, and the Y-axis is the temperature.

Figure 4 is graph of a probe response as a function of thermal capacity (Cp) for a constant conductivity (k=0.5). The X-axis is the time, and the Y-axis is the temperature.

Figure 5 is a normalised version of Figure 3 also showing the time when the heater is on (8).

Figure 6 is a normalised version of Figure 4 also showing the time when the heater is on (8).

Figure 7 is a graph of calorimetric probe output in sand and ϊn loam. Sand is indicated by the concentric circles, loam by the single circle. The X-axis is the percentage water, and the Y-axis is the temperature rise in degrees C.

Figure 8 is a graph of the response of the probe disclosed herein for sand, the upper curve being a dry sand sample, the lower curve being a sand sample which contains 15% water. The X-axis is the time in seconds, and the Y-axis is the temperature rise in degrees C.

Figure 9 is a graph of the response of the probe disclosed herein for loam,

the upper curve being a dry loam sample, the lower curve being a loam sample which contains 15% water. The X-axis is the time in seconds, and the Y-axis is the temperature rise in degrees C.

Figure 10 is a normalised version of Figure 8.

Figure 11 is a normalised version of Figure 9.

Figure 12 is a graph of the time response of a calorimetric probe in sand. The X-axis is the time in hours, and the Y-axis is the temperature rise in degrees C.

Figure 13 is the drying out response with expansive loam. The X-axis is the time in hours, and the Y-axis is the temperature rise in degrees C.

Figure 14 is a cross-sectional diagram of a probe exhibiting the invention disclose herein in one prefered embodiment.

Figure 15 is a sketch of a probe.

Figure 16 is a schematic diagram in cross-section of the probe illustrated in Figure 15 in the ground.

Figure 17 is a schematic diagram in cross-section of the probe illustrated in Figure 15 in the ground further illustrating source of heat (9) and the temperature peak detector (7).

Figure 18 is a schematic diagram of a moisture probe controller and soil moisture detection system in block diagram form.

Figure 19 is a block diagram of a moisture probe controller logic flow. This illustrates the steps involved in utilising the invention in one form.

A description now follows firstly of more of the rationale by which the characteristics of the apparatus and the method have been established and co-jointly with the description of the method, a description of the apparatus which has been found to be most useful for the concept. Firstly a discussion of probes of previous form is given then a discussion of probes made according to the invention.

There has been underta ed a number of tests on probes of previous form, in which the soil surrounds the probe, and it has been observed that without exception, the output quantity of these devices is not a linear function of moisture content.

In fact, it is highly non-linear, where the probe output changes rapidly when the soil is virtually dry (too dry for irrigation practice) and very slowly over the useful range of moisture content.

See Figure 1 for an example. This computerised test involved reading a probe at regular (30 minute) intervals in an electronically weighed sand sample, which slowly dried out. The flatness of the curve in the 3 to 15% moisture content range implies that the tested device would be very inaccurate in the field.

A study was made to answer the question as to what causes the non-linear response and what can be done to improve it.

The probe studied was a solid cylinder of stainless steel 16mm dia. by 40mm long, incorporating a heater and temperature probe. The measurement basis was that of a thermal pulse, i.e. a precise energy (65 Joules) over a precise time (10 seconds) was "pumped in", and the temperature acquired throughout the resulting pulse (typically for 20 minutes). Figure 2 is an example of the form of output.

Two primary thermal property variables combine to affect the output pulse: the thermal conductivity (k) and the thermal capacity (C) of the soil. Published data on the value of these quantities for moist soil are virtually non existent, and never seem to specify soil type, compaction density and moisture content, all of which are required to make a published figure meaningful.

However, published figures for k and C do exist for silica, water and air, which would represent the main constituents of soil. A study of these values, if compaction is assumed to be fixed, indicates that the k of soil may be a fairly weak (and ill-defined) function of moisture content, while C should be a strong and linear function of moisture content.

This means that a thermal probe should be arranged to respond as much as possible to the specific heat C, and as little as possible to the conductivity k, and gives us the clue that the tested probe with its poor linearity may be responding primarily to k.

In order to understand the thermal dynamics better and due to the experimental difficulties in setting up experiments with known conductivity and capacity soils, a mathematical model was written.

The objective was to model the probe so that a response could be predicted for various values of the input parameters of k and C, to see if the probe tested was actually measuring primarily k or C or a combination of both.

The results of this model (an axi-symmetric solution to the transient Fourier equation for heat conduction) shown on Figures 3 and 4 confirm that the model behaves qualitatively the same as the actual probe. Figure 3 shows the responses where k varies by a factor of 4 with C constant, and Figure 4 shows the responses where C varies by a factor of 4 and k is constant. The answer to the above question is that clearly the probe responds to both k and C.

While we can safely say that C varies linearly with moisture, we cannot make any such assumptions for k. Hence the non-linearity of the actual probe must be the influence of its sensitivity to k. Indeed k will depend quite strongly on the compaction due to the presence of air (a good insulator).

A further effect that cannot be overlooked is that of soil shrinkage as it dries. If the probe is sensitive to k, then it will be strongly affected by shrinkage cracking which is almost bound to occur at the probe interface with the soil.

Perhaps this is the mechanism which is responsible for the strong response when the soil is nearly dry: the probe is merely measuring the air gap. This was able to be confirmed to a small degree by re-compressing the soil around a probe as it dried.

Another interesting feature can be obtained from the results on Figures 3 and 4. Although it may appear that k and C have the same effects, a close look at the shape of the temperature decay curve shows a marked

difference. Intuitively this should be the case. As the pulse dies away, the heat flow becomes less transient and more steady state. Steady state heat flow is determined entirely by k and not by C. Now when we rescale the data of Figure 3 to Figure 5, and Figure 4 to Figure 6, such that we normalise the peak temperatures, the difference between response to k and to C is immediately obvious. Varying k will change the time constant of the decay, while varying C does not affect it.

This is a sad fact. If it were the other way around, then our probe could be arranged to measure C and eliminate the vagaries of k, merely by data processing.

To return to the subject of the problems of thermal probes, the outcome of this work is that probes surrounded by soil cannot escape unwanted dependence on the soil conductivity. This has lead to the invention.

The geometry is wrong to achieve otherwise, because the heat flows outwards more-or-less radially, and the dissipation from the probe has to pass through a small area into a large thermal volume. Inherently, the conductivity must dominate, and thermal capacitance alone is not being measured.

The aim is to measure soil thermal capacity with minimal influence of conductivity.

Figures 14, 15, 16 and 17 illustrate an embodiment of the invention in which Figure 14 is a cross sectional view of a body adapted to be inserted within the soil the moisture of which is to be detected,

Figure 15 is an external perspective view of the body as shown in Figure 14,

Figure 16 illustrates the same cross sectional view as in Figure 14 encompassed by and having inserted there through, soil the moisture content of which is to be assessed, and finally

Figure 17 is a schematic view including the view of Figure 16 illustrating the respective inputs and outputs that will be expected for moisture assessment purposes.

Referring in detail to the drawings, the body 1 is shaped so as to have an external cylindrical surface and an internal cylindrical surface shown at 2 these surfaces and the body generally being defined by a hollow co-annular shape formed from plastics material to provide thermal insulation.

Assisting to define the inner cylindrical core 2 is a cylindrical metallic part 3 which includes at one part an electrical resistance member 4 to provide a heating effect.

A temperature detector 5 detects through the medium of the metallic member particularly a non-corrosive conductor and is adapted to detect the temperature reached of soil within the cylindrical area 2, both the electrical resistance 4 and the temperature detector 5 being coupled to be connected through electrical conduits shown collectively at 6.

These are directed to an above the ground position of which there is provision for supply of a square pulse of electrical energy 9 of a selected level for a selected period of time and there is then means responsive to the temperature detector 5 so that a peak temperature reached can be determined and from this, a temperature differential resulting from the pulse of energy, assessed.

In accord with the further rationale, such a level can be correlated against an expected moisture level of the soil.

In use, the cylindrical aperture within the body 1 is filled with soil of the same type for which the moisture is to be assessed and is then inserted at an appropriate depth in the soil.

In order then to assess the moisture level, a burst of energy perhaps typically 75 joules of energy over ten seconds is supplied through the electrical connections and the resulting temperature observed through the peak temperature detection means 7 within which there are means to store the detected such peak temperature and to provide as an output in this here indicating then the temperature differential achieved from an existing temperature to the peak temperature.

The sample should be matched to the surrounding soil, so that the calorimetric potentials equate.

An alternate to a soil sample can therefore be provided.

Note that the heat flow is radially inward in contrast to the dissipative form of the device described previously. The heat enters the sample through a large contact area relative to the thermal volume, and the dimensions are such that the sample reaches thermal equilibrium with the metal ring in a short time relative to the time it takes for conduction to the outside soil to occur. The metal ring is insulated on all external surfaces, to minimise losses.

It is operated on the thermal pulse principle, and the reading can be obtained by measuring the peak temperature rise (PTR) resulting from a fixed energy injection. Although conduction losses will necessarily occur, they will be small at the time taken for the peak temperature to occur.

A preliminary calibration curve for a prototype unit is given in Figure 7. Contrast this with a Figure 1 to observe a much improved characteristic. Although there is some scatter evident, much of which can be attributed to the resolution of the A to D converter used, there is a strong indication that a single calibration may be sufficient for a wide range of soil types, a feature not shared by the conventional probe.

The proof of the superiority of this probe lies in the results presented in Figures 8 to 11. We wish to show that the PTR responds strongly to C and only weakly to k, and is therefore a reliable determination of moisture content for a wide range of soil types. If the PTR were strongly dependant on k, then the device is adversely affected by both soil type and shrinkage effects.

It was discussed above how the k affects the rate of temperature decay but C does not. This probe also exhibits a decay due to conductive heat transfer away from the probe,, but it is slowed by the small area for transfer into the bulk soil, and is of no great consequence to the PTR. Nevertheless, by observing the decay, we also have an indication of the k of the soil.

To labour the point a little, this probe can measure two quantities. The PTR is a strong indicator of C, while the decay is a good indicator of K.

Four samples were tested. Two were sand at 0 and 15% moisture content, and two were loam at 0 and 15%. Figures 8 and 9 show the temperature pulses obtained from these samples. Observe that for these samples, either sand or loam at 0% produce the same PTR. Correspondingly, either sand or loam at 15% produce the same PTR. This is saying that the PTR is not dependant on the size of the particles, as should be expected if PTR is primarily a function of C.

Now also observe that the decays (i.e. k, the conductivity) varied a lot between wet and dry sand, and only a little between wet and dry loam. (To aid this visualization, Figures 8 and 9 have been normalised an replotted on Figures 10 and 11). This means that a probe measuring primarily k, which the conventional probe is, will have a different calibration curve for each soil type.

A test to confirm the time response was done. This was to confirm that with the internal dimensions of the prototype unit, the time taken for the sample inside the probe to equilibrate was not inordinately long. Figure 12 shows this result, indicating a satisfactory equilibration time.

A further test to confirm immunity from shrinkage effects was made by running a test in which a sample of expansive soil was progressively dried out. The plot of PTR against time in Figure 13 shows no characteristic sign of cracking, which was identifiable in previous tests by a sudden jump.

While one indication of the method by which the moisture content has been given, it will be clear that it is not intended that the invention should be limited to this one method only.

It will be understood from the previous description, that by providing an enclosing cavity which is substantially insulated thermally from a remainder of the soil a retardation of losses from the soil being heated is effected thus changing significantly the time constant of losses that can be expected from such a sample as compared to the losses that would be normally effected by soil conduction.

One illustrative implementation of the probe is in the form of a retro-fit to existing automatic irrigation controllers, which simply disables one or more of the solenoid operated valves when the probe indicates that the soil is wet enough.

This has the potential to save a considerable amount of water now being unnecessarily applied by the controllers which have no way of knowing if (a) there has been sufficient natural precipitation to cover the needs of the vegetation or if (b) the irrigation program is applying excessive water for the current atmospheric conditions affecting evaporative and transpiration loss of soil moisture. It should be noted that such controllers would normally be programmed to deliver adequate water for the driest conditions. Thus on average more water than required is being applied.

It is possible to make a unit drawing its power from the host irrigation controller 10 which periodically samples the soil moisture content, and opens a relay 17 connected in series with the required solenoid operated valves 11 when it detects sufficient moisture, thus inhibiting the automatic watering.

This is an ideal application for a very simple microcontroller, such as the Intel 8048. A block diagram of one scheme is shown in figure 18, and a corresponding logic flow diagram in figure 19 explaining in principle how the software could work.

The moisture probe controller 12comprises hardware including a microprocessor (uP) 21 with a minimal number of peripherals, providing the following functions:

- a transistor switch 20 enabling the uP to control the heater 24 in the probe

- a method of displaying the moisture content 23, such as a series of ten LEDs (light Emitting Diodes)

- an irrigation cutout relay 17 and an indicator LED 22 to show its status

visually

- a voltage to frequency (V/F) 19 converter or analogue to digital (A/D) converter, enabling analog voltages to be quantified by the uP

- a multiplexer 18 enabling one of several analog voltages to be switched in to the V/F converter

- push button switch and potentiometer 16 accessible to the user, enabling the user to set the value of soil moisture content below which irrigation is allowed

- a regulated power supply 13

- internal trimming potentiometers 14 and 15 and switches enabling factory calibration and/or selection of operating modes.

The software comprises a single main loop which periodically makes a determination of the soil moisture.

It determines the soil moisture by pulsing the probe heater 26 with a regulated voltage for a precise time interval, then sampling the temperature rise with a temperature detector 27 and identifying the peak. This is then stored in a memory location, overwriting the previous determination.

When a determination is not being made, the loop merely compares the soil moisture with the set point, and operates the irrigation cutout relay accordingly. Some modes of operating may incorporate an algorithm to low pass filter determinations and/or delay the relay actuation to allow a controller to complete a watering cycle, for example.

When the controller is idle, the set point can be adjusted by pressing the button and turning the potentiometer. In this mode, the display displays the value of the set point.

The logic shown is Figure 19 is a follows. The start 39 is followed by a system initialisation 28. Then the system is ready for use.

The controller in step 29 is required to determine if the set point button is pressed. If not the next step 30 is to determine if the main timer has expired, if yes then the controller displays the setpoint in step 38 and proceeds to step 34 where it is determined if the set point button is still depressed. If yes, then the controller loops back to step 38. If not, then the controller proceeds with step 30.

When the main timer has expired, the controller proceeds form step 30 to step 36 where it resets the main timer, reads the temperature as determined temperature detector 27, turns the heater 26 on for a period of time, reads the peak temperature detected, and then determines the moisture content of the soil.

If the main timer has not expired or after step 36 has been done then the controller performs step 31 which is to display the moisture content.

The next step in the logic flow is to determine if the soil moisture content is greater than the set point. If yes, then by step 33 irrigation is inhibited, if not, then irrigation is allowed by perfoming step 37.

Once step 33 or 37 have been performed then the controller returns to step

29.

This is only one of a number of possibilities for application of the soil moisture probe.

This however illustrates the way in which the techniques can be changed while still keeping within the spirit of the general invention.

The disclosed herein moisture probe can provide a moisture probe which is substantially responsive to the moisture content of the soil without being overly subjected to other soil characteristics, easy to produce and maintain. It is therefore an object of the present invention to provide a moisture probe which will obviate of minimize any one of the foregoing disadvantages in a simple yet effective manner or at least provide the public with a useful choice.

While reference has been made to use of a soil sample, it will be clear that this can be replaced with a material that can perform the function of this

without being the sample itself. Obviously then the cavity can be filled with perhaps a fibruos material which will exhibit the same water take up characteristics as the soil but does not need to be inserted freshly from time to time if a probe is relocated.