AU728930B2 - Soil moisture profiling system - Google Patents

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant: Actual Inventor(s): Address for Service: Invention Title: Details of Associated Provisional Application(s) SOIL MOISTURE TECHNOLOGY PTY LTD Jeffrey Bernhard Smith

INTELLPRO

Patent Trade Mark Attorneys Level D, 308 Edward Street, BRISBANE, QLD, 4000 (GPO Box 1339, BRISBANE, 4001) "Soil Moisture Profiling System" No(s): Australian Patent Application No. P02915 filed 11 October 1996 and P07004 filed 27 May 1997 The following statement is a full description of this invention, including the best method of performing it known to me: ,I

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2 "SOIL MOISTURE PROFILING SYSTEM" TECHNICAL FIELD OF THE INVENTION THIS INVENTION relates to monitoring soil moisture and in particular but not limited to monitoring soil moisture for the purpose of irrigation management.

BACKGROUND ART The applicant has reviewed the present methods for monitoring soil moisture for irrigation management and has found that those present systems are very expensive but also fail to provide the farmer or other crop manager with a suitable, immediate, infield reckoning of soil moisture that can be used to manage irrigation.

10 Another problem with the prior art is a lack of genuine portability.

The applicant set out to overcome these deficiencies and has devised a number of separate inventions that can be utilised independently or in synergistic combination. The applicant reserves its right to divide the present application into separate divisional applications as a consequence of the results of international 15 searches or during prosecution of the application.

OUTLINE OF THE INVENTION In one aspect therefore, the present invention resides in a microprocessor controlled, hand-held portable display device for use with a soil moisture sensing assembly, the sensing assembly being adapted to provide signals indicative of moisture contents at selected ones of a plurality of predetermined depths within a soil profile, the display device being arranged for removable connection to the assembly for receiving the signals and comprising a programmable microprocessor control unit and a display unit, the control unit being programmed to display on the display unit information concerning amount and distribution of soil moisture in the soil profile, the information corresponding to the signals received from the sensing assembly.

In one preferred embodiment the display device is used in the display device according to claim 3 wherein the control unit including means for calculating and displaying available moisture based on signals corresponding to readings from the sensing assembly and the control unit is arranged to control storage of the readings taken at different times for the soil profile at any particular location and to *subsequently manipulate the stored readings to provide a readout of water usage by plants and evaporation for that location over a predetermined period of time.

The tube is typically a cylinder and the head is typically piston-like and usually has one or a plurality of rings that help to position the head within the cylinder so that the geometry of measurement is reproducible. In a preferred form, :the tube is made from PVC, but any suitable material can be employed.

S 15 In order to ensure the moisture levels sensed are indicative of the actual moisture levels in the surrounding soil, in one preferred method the tube is installed S•by initially excavating a marginally larger hole and carefully replacing soil around the tube in the same layers as it was removed. The soil is then saturated to bring it up to field capacity and to ensure proper coupling between the soil and the tube.

At this time, while the soil is at field capacity, measurements are taken to determine the moisture holding characteristics of the soil when at full saturation. Soil samples can be removed and dried to determine calibration values. Alternatively soil samples are taken as the hole is being excavated to record soil types and determining soil moisture levels for calibration.

In a second preferred method the tube is installed by initially excavating a hole having a size slightly smaller that the tube and then ramming the tube into the hole. This method results in a relatively good coupling between the surrounding soil and the tube, and thereby relatively more accurate measurements can be obtained. It is preferred that the hole is so rammed that its dimension is substantially the same as the outside dimension of the tube.

The second method is suitable for any soil type, and especially suitable for 10 heavy soil. For gravely of stony soils, a slurry may be used to fill any voids caused by dislodged gravels or stones during excavating. The slurry is typically applied by a backfilling technique.

In a preferred form of the second method the excavating and the ramming are performed in a single process. In this form a drilling bucket or auger of an appropriate size is inserted into the tube positioned substantially vertically on the ground. As the hole is being excavated by the drilling bucket or auger the tube is rammed into the excavation.

Desirably the leading edge of the tube is reinforced with a material having a property that allows ramming with no or little damage to the tube.

The wand is typically made from lightweight aluminium tube and houses an electrical cable inside the tube and extending to the head and out from the proximal end of the wand to a portable computer means and display. While the assembly can include means to automatically detect the position of the wand within the tube, the wand typically includes gradations along its length so that the position of the head within the tube can be measured directly off the wand and measurements taken at predetermined depths.

The sensing head is preferably cylindrical having a top, a bottom and a side wall, a pair of spaced rings projecting from the side wall and being adapted to uniformly slidingly impinge upon the inner wall of the tube, the rings being adjacent the top wall and the bottom wall respectively, the head comprising an equivalent LC (Inductance-Capacitance) circuit comprising of conducting rings .surrounding the side wall and forming an inductor, the inductor having inherent capacitance varying in accordance with the dielectric formed by soil and moisture outside tube and surrounding the rings such that moisture content of soil adjacent S" the tube can be sensed using variation in frequency caused by variations in capacitance.

Preferably, the sensing head is the inductive part of an inductive-capacitance 15 radio frequency oscillator whose frequency is suited to the detection of the dielectric constant variation as the soil moisture levels change.

The inductance consists of a coil of a thin 10mm wide strip of copper or other conducting medium. Alternatively it can be wound from 10 millimetre wide copper tape. This gives the inductance of the inductive-capacitive oscillator a dual purpose. Not only is it the inductance but the wide conductor used in its construction forms the plates of the capacitance part of the LC oscillator. The soil and moisture mixture between these plates is the dielectric. The dielectric constant of the material that is between the plates of a capacitor magnifies the value of the capacitor. The dielectric constant of air is taken as one Dry soil is approximately four and water approximately eighty So that the combined mixture of soil and water will have a dielectric constant between 4 and a value that is the result of the soil water mixture.

The frequency of oscillation will be directly proportional to the value of capacitance across the tuned circuit of the LC oscillator. The value of the capacitance will be magnified by the change in the dielectric constant of the medium between the plates of the capacitor -this medium is the soil water mixture.

The frequency of oscillation will be directly proportional to the change in soil 10 moisture levels.

The guide means can be any suitable means but typically is a tube cap locatable over the proximal end of the tube and including a wand guide-way holding the wand at a generally central position within the tube.

In another aspect, the invention resides in computer controlled, hand-held 15 display unit for use with a sensing assembly, the sensing assembly providing a signal indicative of moisture content at selected ones of a plurality of predetermined S" depths within a soil profile, the display unit having means displaying graphical information concerning the amount and distribution of moisture in the soil as sensed by the sensing assembly. Preferably, the display unit includes means calculating and displaying the available moisture from the readings. Preferably, the display unit enables storage of readings taken at different times for any particular location and subsequent manipulation of those readings to provide a readout of 4 1 water usage by plants and evaporation forthat location over a predetermined period of time. Typically, the predetermined period of time can be hours, days, weeks or months.

In another aspect, the present invention resides in a method for the management of irrigation for commercial crops, the method comprising the steps of:providing a plurality of measuring tubes distributed over an area to be managed; (ii) periodically taking readings indicative of moisture using a sensing assembly having a head displaced longitudinally within the tubes as C.o e 10 readings are taken, the sensingassembly providing a signal indicative of moisture content to a portable hand-held unit capable of providing immediate read out of moisture levels; (iii) storing the readings in the hand-held unit, the hand-held unit having direct on-site display displaying measurements indicative of water 15 content of the soil; and subsequently using that reading as an aid for management of irrigation of the site.

In circumstances where the soil moisture sensor encounters different soil types where stones, tree roots etcetera are present adjacent the tubes it is preferable to employ a method to "calibrate out" these anomalies as the sensor is prone to give an incorrect reading at the location where the stone, root or the like is located.

In these cases the installation of the tube in the soil so that the sensor head R"sees" a truly representative sample of the soil and water mixture is not difficult in 8 soils that are consistent in their composition in terms of particle size, and particle size distribution adjacent to the tubes. However, soils that are stony or gravelly in nature will have an inconsistent characteristic in terms of sensor response even though they may hold the same amount of average moisture. If the stones are of a non-porous type then they will not hold any water. The sensor will thus produce a result that is not truly indicative of the average soil water content.

In order to overcome this problem in these particular circumstances the method includes the additional step of correcting the reading at any point while the soil surrounding the hole is at field capacity. In other words, the invention provides 10 a computer means whereby predetermined values are entered from published data corresponding to the actual field capacity and while the soil is wetted to field capacity measurements are taken and the measurements taken corrected to the expected value at field capacity. Therefore where a measurement is taken adjacent to stone an incorrect lower value would be logged unless a correction is made to 15 lift the value at that point up to field capacity. Thus the calibration step calibrates *out the existence of the stone at that point and takes into account its presence therefore elevating the value to give a true reading of the moisture content at that point when readings are taken in the future.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the present invention can be more readily understood and be put into practical effect, reference will now be madeto the accompanying drawings which illustrate a preferred embodiment of the present invention and wherein:- Figure 1 is a schematic drawing of a site managed using the method according to the present invention; Figures 2A, 2B and 2C illustrate methods of installation of a measuring tube; Figure 3 illustrates a typical wand and sensing head assembly; Figure 4 is a diagram illustrating the sensing head in circuit form; Figure 5 is a view illustrating the typical form of the hand-held display unit; Figure 6 illustrates the principles used in the present invention to calculate and manage irrigation of a site; to- Figure 7 is a typical example of a display of the moisture profile in a S* 10 particular tube; Figures 8A and 8B are alternate flow diagrams illustrating the process by which the computer means, in conjunction with the operator, logs readings for a particular tube and Figure 8B illustrates the process by which the raw data is displayed as a bar graph in accordance with Figure 7; 15 Figures 9A and 9B are alternate flow diagrams illustrating processing of data by the computer means to provide a read out of the amount of water required to S* bring soil back to field capacity; and Figure 10 is a flow chart illustrating processing of data to display a histograph of the rate of water usage with respect of time at different depths within a particular tube.

Figure 11 illustrates use of the present invention in soil where the stones are located close to the tube and there is a requirement to correct to eliminate anomalies arising from the presence of these stones; Figures 12A and 12B are flow charts illustrating the calibration processes utilised in relation to the situation illustrated in Figure 11.

DETAILED DESCRIPTION OF THE DRAWINGS Referring to the drawings and initially to Figure 1, there is illustrated a site 10 where a plurality of measuring tubes 11 are used, one of which is shown in cut away having been located generally vertical in soil on the site to enable soil moisture readings to be taken. The readings are taken using a totally portable unit as illustrated at 12, the unit having a wand 13 and a sensing head 14 from which a signal is delivered along a cable 15 to a display unit and computer means 16.

This apparatus enables the sensing head 14 to be pushed down into the tube 11 and readings taken at intervals along the tube and for those readings to be i displayed on the display unit 16 in terms of percentage moisture content or millimeters of water per 100 millilitres of soil.

Figures 2A and 2B illustrate how tube 11 is installed and as can be seen in Figure 2A, a marginally larger hole is excavated and this is carried out carefully so that the soil surrounding the tube can be replaced. This ensures reliability of readings and so that the soil characteristics, in terms of moisture holding capabilities, are consistent adjacent the tube where readings are to be taken when compared with strata further away from the tube.

Figure 2C illustrates an alternative method where a hole with a diameter about the same as the internal diameter of the tube 11 is excavated using a drilling bucket or auger (not shown) and the tube 11 is rammed into the hole. This method 11 give a very good coupling between the soil and the tube 11 and more accurate measurements can therefore be taken.

The excavation and the ramming can be operated in a single process by positioning the tube 11 vertically over the location where measurements are to be taken and inserting the drilling bucket or auger into the tube 11. The tube 11 is rammed in as soon as the hole is being excavated.

For gravelly and stony soil it is possible that gravels and stones may be dislodged during excavation and as a result the hole has voids left by the gravels or stones. In this case backfilling with a slurry is carried out before ramming so that 10 the voids are filled. This again improves the accuracy of the measurements.

The tubes will be placed on site according to strategic locations where it is thought that soil characteristics vary, for example, a tube may be placed in a basin whereas another tube may be placed on a hill and so forth in order to maximise and optimise the benefits of the system to the irrigator.

••o .oo 15 Figure 3 illustrates the sensing assembly in more detail and as can be seen, ~the head 14 is generally cylindrical and is formed effectively so as to operate pistonlike within the tubes 11. To this end, the head is provided with rings 17 and 18 which engage the inner wall of the tube and a guide in the form of a tube cap 19 guides the wand 13 so that it remains upright and equally spaced from the edges of the tubes 11. The rings 17 and 18 serve to also locate and keep the head straight within the tube. The head has a LC circuit including an inductor, and this is formed by copper rings 20, 21 and 22, the rings being approximately 1 cm wide and being 'Z\\spaced as shown in Figure 3. The wand 13 includes, in this case, graduations 12 shown generally at 23 so that the position of the wand can be read off directly by a user as the wand slides past the cap 19.

Figure 4 illustrates the principle of operation of the sensing assembly comprised in the head 14 and in the present case, a radio frequency oscillator 24 consisting of an active semiconductor and inductance made up of rings 20, 21 and 22, these rings 20, 21 and 22 also have inherent capacitance shown generally at so that the LC circuit thereby formed osci llates at a frequency dependant upon the capacitance. As the capacitance is dependent upon the dielectric and the dielectric dependent upon the nature of the soil and its water content, changes in the water S 10 content, for a particular soil, will bring about a change in frequency. This change in frequency is related to the moisture content and is a reading indicative of moisture content. This change in frequency is firstly processed through a frequency divider at 26 and is then sent to the computer means at 16 where the frequency is oo measured in a counter to determine the frequency in cycles per second or Hz. This number is then used in display and calculation of the soil moisture quantity. The processing is discussed below in relation to the flow charts of Figures 8A through The moisture quality can be expressed in terms of water per 100mm as in Figure 8 or percentage as in Figure 8A. The quality is displayed for each measurement.

The quality can be indicated as a percentage representation. The moisture percentage for the percentage display is a number in the range 0 to 100% and this _is displayed for each measurement. 100% is the value at field capacity, that is, field 13 capacity is the maximum amount of water a soil can retain under field conditions assuming normal drainage and is therefore the "fill" point to be targeted in irrigation.

Figure 6 is a diagrammatic representation of soil moisture, the method of calculating the gravimetric soil moisture is the water content in mm or the weight of water in grams expressed as a percentage of the weight of the dry soil. The soil sample taken when the tube is installed, can be taken away and dried, weighed and then later saturated up to field capacity to determine its maximum water holding capability. Alternatively, if the soil characteristics can be clearly observed, then an S 10 approximate figure for the soils water holding characteristic can be obtained and this can be used for calibrations as the measurements obtained with the present device provide a guide only and usually other factors are also involved in determining the extent of irrigation required.

When using the present invention, soil moisture values calculated from raw 15 data are used to draw a horizontal bar graph from a graphing routine in the computer means. A logging program illustrated in Figures 8A and 8B allows an operator to store the sensor value for each selected depth in memory by depressing a "log" push-button on the key pad. These buttons are illustrated in Figure 5. The operator determines to push the log key pad at intervals as read directly from the wand as it passes through the guide.

When the profile has been recorded, the overall vertical bar graph of the whole soil profile is displayed. This is displayed as vertical bars representing the soil moisture as a percentage of field capacity for each point in the profile that has 14 been logged. Alternately the bar graph can be adapted for indicating water quality in mm per 100mm of soil for each point in the profile. Figure 7 illustrates atypical bar graph for a single tube and Figure 8B illustrates the processing that gives rise to it.

The computer means then calculates the available soil water in millimetres using a water balance calibration program. This is carried out using the procedures set out in flow chart of Figure 9B. An example is given in the following table:- Measurement Depth mm Calibration Water mm F/Capacity Deficit Total Deficit 100 0.15 7.2 15 7.8 7.8 200 0.15 8.25 15 6.75 14.5 300 0.15 9.3 15 5.7 20.25 400 0.18 8.1 18 9.9 30.15 500 0.18 8.28 18 9.72 39.87 600 0.2 9.4 20 10.6 50.47 700 0.2 11.6 20 8.4 58.87 800 0.3 18.6 30 11.4 70.27 900 0.3 21.0 30 9.0 76.27 1000 0.3 22.5 30 7.5 86.77 TOTAL 124.23 211 86.7 r c r In Figure 9B a water balance calibration number is used to convert the percentage figure into millimetres of water in the soil over the depth of measurement. An example is given in the following table:- Measurement Depth mm 100 200 300 400 500 Calibration 0.15 0.15 0.15 0.18 0.18 Water mm 7.2 8.25 9.3 8.1 8.28 F/Capacity 18 18 600 47 0.2 9.4 700 58 0.2 11.6 800 62 0.3 18.6 900 70 0.3 21 1000 75 0.3 22.5 TOTAL 124.23 211 The precipitation required to bring this one metre soil profile up to field capacity would be 86.7mm, if the irrigation sprinklers have a precipitation rate of per hour, then one would need to water for 2.5 hours. If the plant or crop root feeding zone only extended to 400mm, then the soil would contain 32.8mm of soil water; field capacity over this depth would be 63mm, to bring this reduced depth up to field capacity would require 30.2mm of precipitation or .86 hours of :watering.

It will be appreciated that once the raw data has been recorded at time intervals over, say, a week, it can be stored and from the data taken, it is a simple matter to manipulate that data in order to obtain a record of how a particular site •go•

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or group of sites have preformed over a particular time period. A typical flow chart for generally this kind of information is shown in Figure S* The problem can arise where soil is not homogenous. For example, where the soil is excessively rocky. If stones are non-porous they will not hold any water.

The sensor will produce a result that is not indicative of the average soil water content. Where the soil I is not consistent near the access tube this gives inconsistent characteristic in terms of sensor response. An example of this is illustrated schematically in Figure 11.

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16 In these situations it is preferable to relate the actual measurements to the values under homogenous soil conditions in order to "calibrate out" any variations due to rocks close to the access tube.

To do this, soil surrounding the entire length of the access tube is brought up to field capacity by applying water to the soil surface.

The process set out in Figure 12 is then followed to calibrate the sensor at any particular site and at any particular point in the site. As can be seen from Figure 11 initially the site is selected, the number of points which is typically ten i. and then auto is selected. The offset figure given to the customer to account for 10 sensor reading at zero percent moisture is then entered. In Figure 9 process the sensor probe is read at the point to be calibrated and the log key is pressed. At this S-stage the raw data is read from the probe and the slope calculated for a hundred percent expected field capacity figure at that point.

In Figure 9B processing, the display now shows millimetres of water at the 15 point of measurement, calculated from a default slope value. The INC and DEC keys on the keypad are now used to change the slope value so that the displayed *"*soil moisture agrees with the actual soil moisture. This may be the value for field capacity or an actual measured value derived from analytical determination for the soil being measured. The slope value generated is stored by depressing the LOG key.

The field capacity is entered from a chartered figure produced from published documents or provided for the particular soil content being used.

For the Figure 9C process the slope is calculated in millimetres of water by converting the number of counts in the reading.

The refill figure is now entered as shown in millimetres of water per hundred millimetres depth of soil depth for Figure 9B process or as a percentage of field capacity for Figure 9A process. The value for this refill point will be determined by the irrigation strategy being employed. The calibration takes place for each point in the access tube and the calibrated figures are retained for future measurement at that site. These calibration values can be entered for sites with the same soil type.

The calibration takes place for each site in the same soil conditions.

Whilst the above has been given by way of illustrative example of the present invention many variations and modifications thereto will be apparent to those skilled in the art without departing from the broad ambit and scope of the invention as herein set forth.

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Claims (9)

1. A microprocessor controlled, hand-held portable display device for use with a soil moisture sensing assembly, the sensing assembly being adapted to provide signals indicative of moisture contents at selected ones of a plurality of predetermined depths within a soil profile, the display device being arranged for removable connection to the assembly for receiving the signals and comprising a programmable ricroprocessor control unit and a display unit, the control unit being i programmed to display on the display unit information concerning amount and *distribution of soil moisture in the soil profile, the information corresponding to the signals received from the sensing assembly.

2. The display device according to claim 1 wherein the information is displayed in a numeral or graphical form.

3. The display device according to claim 2 wherein the device further *eee comprising storage means, the control unit being selectively controlled to store the 15 information in the storage means so that instant and/or any stored information can be selected for displaying on the display unit.

4. The display device according to claim 3 wherein the control unit including means for calculating and displaying available moisture based on signals corresponding to readings from the sensing assembly and the control unit is arranged to control storage of the readings taken at different times for the soil profile at any particular location and to subsequently manipulate the stored readings to provide a readout of water usage by plants and evaporation for that location over a predetermined period of time. 19 A soil moisture sensing assembly comprising an elongate wand having a proximal end and a distal end, a sensing head at or adjacent to the distal end of the wand, and a separate measuring tube, the sensing head being of dielectric measurement type and being configured for longitudinal displacement within the separate measuring tube, the measuring tube having a proximal end and a distal end and being positioned, in use, below soil level and generally vertically in a soil profile, the relative dimensions of the tube, the sensing head and the wand being i so made and arranged that the wand can be manually manipulated and displaced :along and inside of the tube so that the head can sense a signal indicative of moisture contents at different depths in the soil profile, and a display device as claimed in any of the preceding claims.

6. The assembly according to claim 5 wherein the assembly including a guide means to aid positioning and guiding of the wand within the tube.

7. The assembly according to claim 5 or 6 wherein the tube is a cylinder and a the head is substantially piston-like and having one or a plurality of rings for S"positioning the head within the cylinder so that the geometry of measurement is reproducible.

8. The assembly accordingly to any one of claims 5 to 7 wherein the assembly is calibrated for moisture holding characteristics in surrounding soil so that levels of the moisture contents sensed are indications substantially of the actual moisture levels in the soil.

9. The assembly according to any one of claims 5 to 8 wherein the wand houses an electric cable connecting the sensing head to the display device, and indication means being provided on the wand for indicating the position of the head within the tube. The assembly according to any one of claims 5 to 9 wherein the sensing head having a top, a bottom and a side wall, a pair of spaced rings projecting from the side wall and being adapted to uniformly and slidingly impinge upon the inner wall of the tube, the rings being adjacent the top wall and the bottom wall respectfully, the head further having an inductance-capacitance circuit comprising of conducting rings surrounding the sidewall and formingan inductor, the inductor having an inherent capacitance varying in accordance with the dielectric formed by soil and moisture outside the tube and surrounding the rings such that moisture

555. contents of the soil can be sensed using variation in frequency caused by the variations in capacitance. "11. The assembly according to claim 10 wherein the conducting rings are ••go •go. formed from a coil of a thin strip or tape of a conducting medium and the rings 15 forming the inductance as well as the plates of the capacitance part of an LC oscillator, and the soil and moisture therein forming the dielectric of the capacitance of the LC oscillating, so that the oscillation frequency varies with change of dielectric constant in the soil-water mixture. 12. A method for the management of irrigation for commercial crops, the method comprising the steps of:- providing a plurality of measuring tubes distributed over an area to be managed; (ii) periodically taking readings indicative of moisture using a sensing assembly as claimed in any one of claims 5 to 11, the assembly having a head displaced longitudinally within the tubes as readings are taken, the sensing assembly providing a signal indicative of moisture content to the portable hand-held portable device which is arranged to provide immediate read out of moisture levels; storing the readings in the hand-held device having the display unit arranged to provide a direct on-site indication of measurements indicative of water contents of the soil profile; and (iv) subsequently using that readings as aid for management of irrigation of the site. 0.00 ooo° 0 o 12. The method according to Claim 11 wherein the method including a 0.0 0calibration step for correcting readings at particular locations. 0 15 13. The method according to claim 12 wherein the calibration step includes 4 4 adjusting readings at any of said particular locations taken while the soil surrounding the hole is at field capacity to correspond to known values at field capacity 14. A microprocessor controlled, hand-held display device substantially as described with reference to Figures 1 to 12. A soil moisture sensing assembly substantially as described with reference to Figures 1 to 12. 16. A method for the management of irrigation for commercial crops substantially as described with reference to Figures 1 to 12. DATED this 1 3 th day of October, 2000 SOIL MOISTURE TECHNOLOGY PTY LTD By their Patent Attorneys INTELLPRO S S S S S 4 S