U.S. patent number 5,033,397 [Application Number 07/562,210] was granted by the patent office on 1991-07-23 for soil chemical sensor and precision agricultural chemical delivery system and method.
This patent grant is currently assigned to Aguila Corporation. Invention is credited to John W. Colburn, Jr..
United States Patent |
5,033,397 |
Colburn, Jr. |
July 23, 1991 |
Soil chemical sensor and precision agricultural chemical delivery
system and method
Abstract
A real time soil chemical sensor and precision agricultural
chemical delivery system includes a plurality of ground-engaging
tools in association with individual soil sensors which measure
soil chemical levels. The system includes the addition of a solvent
which rapidly saturates the soil/tool interface to form a
conductive solution of chemicals leached from the soil. A
multivalent electrode, positioned within a multivalent frame of the
ground-engaging tool, applies a voltage or impresses a current
between the electrode and the tool frame. A real-time soil chemical
sensor and controller senses the electrochemical reaction resulting
from the application of the voltage or current to the leachate,
measures it by resistivity methods, and compares it against pre-set
resistivity levels for substances leached by the solvent. Still
greater precision is obtained by calibrating for the secondary
current impressed through solvent-less soil. The appropriate
concentration is then found and the servo-controlled delivery
system applies the appropriate amount of fertilizer or agricultural
chemicals substantially in the location from which the soil
measurement was taken.
Inventors: |
Colburn, Jr.; John W. (Houston,
TX) |
Assignee: |
Aguila Corporation (Houston,
TX)
|
Family
ID: |
24245280 |
Appl.
No.: |
07/562,210 |
Filed: |
July 31, 1990 |
Current U.S.
Class: |
111/118; 47/1.3;
111/200; 204/400; 324/347 |
Current CPC
Class: |
A01M
7/0089 (20130101); G01N 27/043 (20130101); A01C
21/007 (20130101); A01C 23/007 (20130101); G01N
33/24 (20130101); A01C 23/02 (20130101); A01B
79/005 (20130101); Y02P 60/21 (20151101) |
Current International
Class: |
A01M
7/00 (20060101); A01B 79/00 (20060101); A01C
21/00 (20060101); A01C 23/02 (20060101); A01C
23/00 (20060101); G01N 27/04 (20060101); G01N
27/416 (20060101); G01N 33/24 (20060101); A01C
023/00 () |
Field of
Search: |
;47/1,1.3,118,DIG.10,1.01 ;73/151,153,864.58 ;175/50 ;204/400,403
;324/347,376 ;364/420,421,422 ;111/1,6,7,118 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Steinberger; Brian S.
Attorney, Agent or Firm: Groves; D. Arlon
Government Interests
This invention was made with Government support under Contract No.
DE-AC07-84ID12518 awarded by the Department of Energy. The
Government has certain rights in this invention.
Claims
What is claimed is:
1. A method for sensing substantially instantaneously at least one
chemical constituent of a soil while traversing a field of said
soil and determining substantially simultaneously therewith an
amount of corrective chemical to be added to said soil, comprising
the steps of:
penetrating the soil of a first soil sample while traversing said
sample;
applying a solvent to said first soil sample to create a leachate
while traversing said sample;
applying a voltage differential across said leachate and
determining a parameter proportional to said soil constituent while
traversing said sample; and
determining the amount of corrective chemical to be added to said
sample while traversing said sample.
2. The method of claim 1 further comprising the steps of:
determining said parameter in the absence of said leachate;
comparing said parameter determined in the absence of said leachate
with said parameter determined in the presence of said leachate;
and
calibrating the determination of said parameter determined in the
presence of said leachate so as to compensate for said parameter in
the absence of said leachate.
3. The method of claim 1 further comprising the step of:
adding the amount of corrective chemical to said soil sample while
traversing said soil sample.
4. The method of claim 1 further comprising the step of:
applying a correlating factor to said parameter determined in the
presence of said leachate in order to correlate said parameter to
the approximate relative concentration of the soil constituent of
interest.
5. The method of claim 4, further comprising the steps of:
receiving from an external source a signal corresponding to said
correlating factor, and
processing said signal into a form suitable for applying as said
correlating factor.
6. The method of claim 4, further comprising the steps of:
receiving a signal generated from operator input information
corresponding to said correlating factor, and
processing said signal into a form suitable for applying as said
correlating factor.
7. A system for sensing substantially instantaneously at least one
chemical constituent of a soil while traversing a field of said
soil and determining substantially simultaneously therewith an
amount of corrective chemical to be added to said soil,
comprising:
means for penetrating the soil while traversing a first soil
sample;
means for supporting a plurality of multivalent electrodes at about
the depth of said soil penetration means;
means for applying a solvent to a portion of the soil at about such
depth and creating a leachate electrically coupling said electrodes
to the soil sample surrounding said leachate; and
means for applying a voltage differential across said leachate
through said electrodes, whereby said system determines the
magnitude of an electrochemical component of said leachate
proportional to the chemical constituent thereof.
8. The system of claim 7 further comprising:
means for adding the amount of corrective chemical to said soil
sample while traversing said soil sample.
9. A sensor system for sensing a chemical constituent of a soil,
comprising:
shank means for penetrating the soil and supporting a multivalent
electrode thereon, said shank means being at least partially formed
of a multivalent conductive material;
means cooperating with said shank means for applying a solvent to a
portion of the soil and creating a leachate electrically coupling
said shank means and electrode to the soil surrounding said
leachate; and
means for applying a voltage differential across said leachate
through said shank means and electrode and determining the
magnitude of an electrochemical component of said soil proportional
to the chemical constituent thereof.
10. The sensor data system of claim 9 wherein a soil penetrating
end of said shank means is crescent shaped.
11. The sensor system of claim 9 wherein said cooperating means and
said shank means comprise a shank having at least one aperture on a
side thereof for providing fluid communication between said soil
and a solvent supply connected to said aperture.
12. The sensor system of claim 11 further comprising soil shielding
means adjacent said aperture for preventing soil from clogging said
aperture.
13. The sensor system of claim 9 wherein said shank means and said
electrodes are formed primarily of dissimilar multivalent
conductive material.
14. The sensor system of claim 9 wherein said shank means and said
electrodes are formed primarily of similar multivalent conductive
material.
15. The sensor system of claim 9 wherein said shank means supports
said multivalent electrode thereon in non-parallel alignment with
the direction of forward motion of said shank means.
16. A system for sensing substantially instantaneously at least one
chemical constituent of a soil while traversing a field of said
soil and determining substantially simultaneously therewith an
amount of corrective chemical to be added to said soil,
comprising:
means for penetrating the soil while traversing a first soil
sample;
means for applying a solvent to said first soil sample to create a
leachate while traversing said soil sample;
means for applying a voltage differential across said leachate and
determining a parameter proportional to said soil constituent while
traversing said sample; and
means for determining the amount of corrective chemical to be added
to said sample while traversing said sample.
17. The system of claim 16 further comprising:
means for determining said parameter in the absence of said
leachate;
means for comparing said parameter determined in the absence of
said leachate with said parameter determined in the presence of
said leachate; and
means for calibrating the determination of said parameter
determined in the presence of said leachate so as to compensate for
said parameter in the absence of said leachate.
18. The system of claim 16 further comprising:
means for adding the amount of corrective chemical to said soil
sample while traversing said soil sample.
19. The system of claim 16 further comprising:
means for applying a correlating factor to said parameter
determined in the presence of said leachate in order to correlate
said parameter to the approximate relative concentration of the
soil constituent of interest.
20. The system of claim 19 further comprising:
means for receiving from an external source a signal corresponding
to said correlating factor, and
means for processing said signal into a form suitable for applying
as said correlating factor.
21. The system of claim 19 further comprising:
means for receiving a signal generated from operator input
information corresponding to said correlating factor, and
means for processing said signal into a form suitable for applying
as said correlating factor.
22. A method for calibrating means for rapidly determining soil
constituent concentrations while traversing a field of such soil,
comprising the steps of:
penetrating the soil of a plurality of soil samples while
respectively traversing such samples;
applying a solvent to said plurality of samples to create a
plurality of leachates while traversing such samples;
appyling a potential across each said leachate and determining the
respective values of a parameter proportional to said soil
constituent while traversing such samples;
determining a first representative value of such respective
values;
comparing said first representative value with a second
representative value; and
calibrating the determination of said first representative value so
as to compensate for said second representative value.
23. The method of claim 22, wherein said second representative
value is determined from a plurality of soil samples obtained from
the traversed portion of such field and analyzed by other
means.
24. A system for calibrating means for rapidly determining soil
constituent concentrations while traversing a field of such soil,
comprising:
means for penetrating the soil of a plurality of soil samples while
respectively traversing such samples;
means for applying a solvent to said plurality of samples to create
a plurality of leachates while traversing such samples;
means for applying a potential across each said leachate and
determining the respective values of a parameter proportional to
said soil constituent while traversing such samples;
means for determining a first representative value of such
respective values;
means for comparing said first representative value with a second
representative value; and
means for calibrating the determination of said first
representative value so as to compensate for said second
representative value.
25. The system of claim 24, further comprising means for receiving
a signal corresponding to input information representing said
second representative value.
Description
RELATED PATENT APPLICATIONS
This application is related to co-pending U.S. patent application
Ser. No. 07/275,266 filed Nov. 23, 1988, now abandoned, which in
turn was related to then-copending U.S. patent application Ser. No.
07/076,055 filed July 21, 1987, which was abandoned upon filing of
related application 275,266.
BACKGROUND OF THE INVENTION
The present invention relates to a novel agricultural chemical
system and method and, more particularly, to a system that senses
the chemical condition of the soil in real time and applies an
appropriate amount of corrective agricultural chemical or
fertilizer in response to a sensed deficit or excess condition.
This system has important benefits in cost reduction, energy
resource conservation, crop production, and reduction of
environmental degradation.
The modern farm practice of applying chemicals to the soil to
obtain optimal crop yield differs little from that used a hundred
years ago, when manure from farm animals and so-called "green
manure" (composed of luguminous crops or harvest detritus) were
added. The farmer, as always, desires sufficient soil fertility to
ensure that a successful harvest will result from his planting. The
methods by which the farmer's objectives are met have advanced
considerably. Cropland productivity is increased many-fold with the
application of specific chemical materials tailored to precisely
provide the plant nourishment or protection needed. Beyond the need
for adequate fertility, the crop is usually also given protection
from competing weeds and insects by the application of assorted
herbicides and insecticides.
Fertilizers and agricultural chemicals are applied by diverse types
of field equipment, including granular spreaders, liquid spray
bars, and anhydrous, solution, or granular injectors. Farmers also
make choices as to when to apply the fertilizer for the next
growing season, such as in the late fall or early spring, while
planting, or after planting. Similarly, agricultural chemicals such
as herbicides are applied at an appropriate stage of weed growth
most likely to destroy or regulate undesireable plant growth.
Assorted variables influence the amount of nitrogen and other
nutrients that are available for plant growth and development. In
the case of nitrogen, local field conditions determine the quantity
of ammonium held on the exchange complex of the soil and the
precise mechanics of conversion to more available forms via
bacterial action. Conversion of variable ammonium levels at
distributed oxidation levels in soils is highly variable from
point-to-point even within fields which appear relatively
homogeneous. Although this extreme variability of soil chemical
levels has been known since at least the 1920's, until now no one
has perfected a method of accounting for this variability while
adding fertilizers or other corrective chemicals such as lime.
Nitrogen exists in the soil in a variety of chemical forms. In the
ammonium form it is relatively immobile, but after transformation
by soil bacteria to nitrate its mobility increases drastically.
Nitrate becomes elusive because of its high solubility in soil
water. Nitrate moves with the soil water in response to soil
temperature changes, rainfall, and crop transpiration demands. The
coefficient of variation of soil nitrate levels typically has a
mean of 50% and often reaches 100% even over small areas of only
several square yards. Similar observations have been made for pH
and potassium levels. Because available nitrogen varies widely,
even when fields have been uniformly fertilized, sporadic,
conventional soil samples cannot be representatve indicators of a
field's nitrogen availability status.
Insufficient nutrient levels will affect crop productivity
adversely; excess nutrient levels will either have a similar effect
or simply be wasted. In the case of nitrogen, soil nitrate
(NO.sub.3 --N) levels above 30 ppm are considered to be wasted
nutrients. Field data indicate that considerable excess nitrate is
available that does not contribute to crop production. Because
nitrate is mobile and does move downward away from the rooting zone
in the absence of a crop, nitrate in the soil at the end of a
growing season may not be available to the next year's crop but may
serve only to contaminate ground water.
Plants use only those nutrients they need and the use of the
nutrients complies with a law of diminishing returns. Above a
certain threshold level, the farmer obtains little yield response
with increasing nutrient level. From an energy efficiency
perspective, nutrients applied above this threshold level are
wasted. In the case of a normal distribution with a large
coefficient of variation (ratio of standard deviation to the mean
value), approximately 50% of the nutrients are wasted. This means
that both the energy and raw materials used to manufacture the
nutrient, as well as the farmer's profit dollars, have been
squandered.
For example, nitrogen in its gaseous form is of no use to plants.
Plants require that nitrogen, in the form of complex nitrogen
compounds, be further transformed into soluble nitrates in order to
be utilized by the plants. All agricultural chemical compounds,
including manure, are toxic to some extent and can contaminate
groundwater, particularly those in the nitrate form. Thus amounts
of fertilizer greatly in excess of what the plants can profitably
use cannot be prudently applied. They are also expensive, which is
another good reason to not overfertilize cropland. Until the
present invention, the farmer has had no practical way to optimize
his application rate, nor to vary his application rate in response
to changing conditions across his field. He has been limited to
simply applying what worked in the past, perhaps aided by his
recollection of how last year's crop came out, perhaps supplemented
by a few spot soil analyses made around the field.
Because of the spatial variations in his field, and because of the
time delay between sampling and receiving results--during which the
soil conditions will have changed--the farmer who has paid for spot
samples is scarcely better able to fertilize his fields than is the
farmer who simply fertilizes on an historic basis. Consequently,
farmers routinely apply excess fertilizer as a protective measure,
and in doing so lower their profit margin and risk groundwater
contamination, neither of which is desirable.
Farmers know, qualitatively, that crop yields vary because
uniformly applied fertilizers are not converted uniformly to forms
useful to plants. Farmers generally use rules of thumb to guide
application timing. Moreover, farmers realize that their only
source of agrichemical recommendations beyond accepted rules of
thumb is either an extension agent or a chemical sales
representative.
Soil sampling, used to aid the farmer in fertilizer application, is
conventionally based on a farmer's own sample timing and site
selection rationale. Chemical analyses of soil samples that the
farmer provides to the extension system agent or salesman require
interpretation by technically trained personnel to reveal nutrient
needs. Often, however, either no nutrient analysis is performed or
the analysis is ignored as meaningless due to the perceived
complexity of the technical issues in agricultural chemical
management. Today, generalized nitrogen management recommendations
are all based on experimental evaluation of different fertilizer
treatment methods. Soil tests are not routinely done for available
nitrogen at the farm level, and the "turnaround" time between
sampling and receiving laboratory results is too long to satisfy
the farmer's needs for the timing of his application. Local,
spatial variations which have significant effects on the crop are
normally not addressed at all.
Accordingly, significant energy waste occurs in the application of
agricultural chemicals simply because no proven, economical method
exists to properly and timely allocate chemicals to meet crop
needs, and agricultural chemicals and fertilizers are consequently
applied in substantially uniform amounts irrespective of local
variations in soil chemical conditions.
In summary, the conventional method of providing agrichemical
recommendations for farm level chemical application includes soil
sampling by the farmer himself and laboratory analyses, resulting
in technically informed interpretations by technically trained
personnel. These recommendations normally are then implemented by
the farmer himself, who usually is not technically trained in these
disciplines.
There are significant sources of error in this multiple-step
process, including, for example, errors unavoidably caused by the
time delay and errors in selecting a truly representative sample,
sample collection and handling, sample preparation and conditioning
in the laboratory, trained interpretation of nutrient needs, and
errors in application of the recommended level due to the
imprecision of the chemical application equipment.
OBJECTS OF THE INVENTION
It is therefore a principal object of the present invention to
provide a rapid soil chemical sensor and application control system
to apply fertilizer and other agricultural chemicals to timely meet
crop and farmer profitability and environmental needs on a local
basis within a field while a farm chemical application vehicle
traverses the field.
It is another object of the present invention to provide a soil
chemical sensor and application control system that utilizes a low
cost, fast response detector that can be applied to or integrated
with a variety of ground engaging tools to detect soil nutrient
levels.
Still another object of the present invention is to provide a soil
chemical sensor recommendation system and a precision application
control system that operates while a farm vehicle traverses a field
without substantial intervention by the vehicle operator.
SUMMARY OF THE INVENTION
In one embodiment, the soil chemical sensor system of the present
invention may be used by itself to accurately determine soil
deficit or excess conditions on a spot basis or throughout a field
for later correction. Preferably, however, it will be used with one
or more ground-engaging tools in association with individual soil
chemical sensors. In a preferred embodiment, a solvent is applied
while the tool or tools are moving past a soil sample, which
rapidly saturates the soil/tool interface to form a conductive
slurry containing dissolved chemicals (leachate) extracted from the
soil. Preferably, a multi-valent electrode, positioned within a
multivalent frame (such as iron) of the ground-engaging tool,
applies a voltage differential or impresses a current between the
electrode and tool frame; a real-time soil chemical sensor
controller reacts to the electrochemical current resulting from the
application of the voltage differential or current across the
leachate and the local soil sample. This transfer, which may be
measured by resistivity methods, is preferably compared to
calibrated resistivity magnitudes for target substances extracted
by the solvent and applied voltage differential or current. If the
user has specified a maximum allowable concentration, the
appropriate proportion of this maximum is then found and the
servo-controlled applicator applies the appropriate amount of
fertilizer or agricultural chemicals in close proximity to the
location from which the soil measurement was taken. If a nutrient
level in excess of the maximum allowable value is sensed, nothing
is applied.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified pictorial representation of a preferred
embodiment of the soil constituent sensor and chemical application
system of the present invention in a typical field operation.
FIG. 2 is a functional representation of the sensing and
application system with a schematic representation of a
ground-engaging device.
FIG. 3 portrays a typical electrochemical resistivity of a nitrate
bearing soil as a function of voltage differential and the
enhancement of such resistivity by the methods of the present
invention.
FIG. 4 is a schematic representation of the main sensory inputs,
fixed inputs, and command outputs of the system.
FIG. 5 is a cross-sectional representation of the soil sampler
shank 12 of FIG. 2, taken at region 11.
DETAILED DESCRIPTION
It is to be understood that the soil chemical sensor and
agricultural delivery system of the present invention, when used to
apply fertilizer, for example, may automatically, without tractor
operator interaction, apply the needed chemicals to soil regions
with low soil chemical levels to bring said levels to the desired
level. The system may be most advantageously used by applying the
bulk of fertilizer a few weeks after crops emerge, as opposed to
the conventional approach which applies high, uniformly applied
pre-plant fertilizer levels. Post-plant application is demonstrated
to be much more efficient than pre-plant application, but has
hitherto been difficult to control properly. In the case of
nitrogen fertilizer, ammonium after conversion to nitrate becomes
the representative parameter for crop nitrogen fertility. It would
be preferable to measure and dispense in response to nitrate, in
contrast to other nitrogen species such as ammonium which may also
be determined by the method disclosed herein. Furthermore, this
system permits the introduction of nitrogen nearer the time in the
growing cycle that the crop needs the nutrient. As a result,
fertilizer is more efficiently used and less fertilizer may be used
to achieve a given increase in productivity.
Referring now to FIG. 1, there may be seen a simplified pictorial
representation of one type of system embodying the concepts of the
present invention for sensing soil constituent levels and
dispensing the needed amount of corrective chemical. More
particularly, there may be seen a farm chemicals application
vehicle 1, commonly a farm tractor, flexibly and removably attached
by adjustable lifting means 2, commonly a three-point hitch, to
sensing and dispensing system 10. The resulting assemblage is shown
being operated in direction 6 over farm soil 5 in which crops 7 are
grown and measuring the concentration of desired soil chemical 8
and supplying farm chemicals withdrawn from a reservoir 4 removably
attached to the frame of the application vehicle attached by hitch
means 3. Crops 7 may include row crops, grasses, orchard crops,
vineyards or any other type of crop in which a mobile vehicle can
routinely traverse the field and for which a soil chemical level
and chemical application are appropriate.
Referring now to FIG. 2, the soil chemical sensor and control
system 10 includes a ground-engaging soil sampler shank 12 which
may take many different forms, such as a knife, harrow, cultivator
tine or the like, and which normally penetrates the soil to a
desired depth. The sampler shank 12 may have a thin and tapered
longitudinal cross-section below region 11 to facilitate soil
penetration and provide intimate soil, shank, solvent, and
electrode contact. Said sampler shank may be configured for use in
various types of farming operations such as conventional tillage,
where rugged anhydrous ammonia application knives are used. In such
an application, the soil sampler shank may consist of a
commercially available anhydrous knife with the remaining elements
of the ground engaging shank 12 of the preferred embodiment
described herein made into a thin plate removably affixed to the
sides of said anhydrous knife. In ridge-till farming, chemical
application is done routinely with cultivators which have
shoe-shaped ground engaging surfaces. The elements of the preferred
embodiment can be suitably built into any of these existing tools.
In no-till farming, application may be conducted in the presence of
surface residual crop debris, requiring a leading coulter 28 to
provide an unencumbered path. For this type of farming, laterally
adjustable mounting means 29 is necessary to insure that at least
one side of shank 12 is held against a side of the kerf 30 produced
by the passage of coulter 28 through the soil 51.
In the preferred embodiment, the sampler shank 12 may be formed of
a multivalent conductive material, such as iron, and may serve as
the larger of the electrodes that applies a voltage differential or
current across and through the solvent-produced leachate and into
the engaged soil 51. The ground-engaging soil sampler shank 12 is
connected to support member 15 which, when coupled to chemical
application vehicle 1 (FIG. 1) in motion, conveys the draft force
necessary to move the system 10 through the soil 51 in the
direction of arrow 13.
The ground-engaging soil sampler shank 12 preferably includes a
solvent orifice 14 on at least one side thereof, and preferably on
both sides, through which a solvent is forced that saturates
adjacent soil to be sampled. A protrusion 20 which may be wedge
shaped, hemispherical, cylindrical or the like is formed on the
leading face of the sampler shank 12, immediately preceeding
solvent orifice 14, and such protrusion 20 acts to prevent soil
from clogging the solvent orifice 14 and to create a saturated path
50 in the soil as the sampler shank moves in the direction of arrow
13. The solvent 52 may be selected to target and limit the species
analyzed from the soil extraction and voltage application or
current penetration. When applying nitrogenous fertilizer, soil
nitrate level is the chemical constituent preferably targeted and,
consequently, the solvent may be aqueous because nitrates are
highly soluble in water. Normally, most solvents used are aqueous
solutions with additives especially selected for analysis of
specific chemicals and/or operating utility. Even for nitrate
analysis, solvents are not limited to water alone and may also
contain additives such as CaCl.sub.2 which, for example, can
depress the freezing point of the solvent. Such additives are
necessary should the sampler shank 12 be thermally connected or
combined with the applicator shank 40 for economy and for the use
of anhydrous ammonia fertilizer which produces reduced temperatures
of the applicator shank 40 when delivered to the soil 51 through
chemical delivery orifice 42. In a preferred embodiment, natural
rainwater, collected in a non-contaminating cistern, is a suitable
aqueous base. Such water normally has a pH of approximately 5.5 and
is suitably buffered for hydrogen ions collected in the leachate.
The solvent is supplied from a solvent storage container 16 which
may embody any suitable material that is non-reactive with the
solvent. Solvent supply container 16 communicates with pressure
pump 17 via conduit 18. Downstream of pump 17 the solvent, under
pressure, flows through manifold 19 to the inlet of flow control
valve 23 which is preferably a fast response solenoid or butterfly
type throttling valve.
In response to electrical signals from control means 31, the
desired amount of solvent for soil saturation at tractor speed is
released through the valve 23 which supplies a manifold 24 and then
to a fixed orifice 25 therefrom by conduit 26 connected to the
ground engaging soil sampler shank 12 via affixed conduit 21 and
therefrom out to solvent orifice 14 on both sides of the sampler
shank. A desireable amount of solvent released is, in the case of
nitrate analysis, approximately 300 ml/minute for each solvent
orifice 14 when the shank 12 is moving in the direction 13 at 8
mph. This amount is adequate to insure that the chemical
constituent being sensed goes into solution, that is to say, an
excess of solvent should be used. Such excess will insure that the
saturated path 50 is at all times conductive for current
penetration of the soil 51, even as farm vehicle ground speed
varies, and that the applied voltage differential or current
withdraws soil chemicals of interest from the soil 51.
A multivalent electrode 22, which is not required to be inert to
the chemical species of interest, is preferably composed of a metal
material dissimilar to that of the shank, has its conducting
surface(s) horizontally aligned with, and spaced rearward from,
solvent orifice 14. While rigidly but removably attached to sampler
shank 12, said multivalent material electrode 22 is nonetheless
electrically insulated therefrom and connected to control means 31
via conduit-protected wiring 54. Multivalent material electrode 22
may be positioned rearward or behind solvent orifice 14 such that
as sampler shank 12 advances in the direction of arrow 13, the soil
slurry, containing leachate promoted by solvent orifice 14, will
make intimate contact with the sides of sampler shank 12, an action
enhanced by the aforesaid tapered cross section and adjustable
mounting means 29, said slurry ultimately reaching multivalent
electrode 22 along saturated path 50. A voltage or current level
obtained from control means 31 connected to power source 27 is
impressed across multivalent electrode 22, which is preferably of a
copper bearing material, and the multivalent iron electrode which
is the body of shank 12. The body of shank 12 is connected to the
opposite polarity reference of the power source 27 by wiring 55.
With a fixed applied voltage, preferably within the range of about
1.4 to 1.8 volts potential difference, between said electrodes, of
which the multivalent electrode 22 is held positive with respect to
the body of shank 12, an electrical current will be conducted
through the nitrate leachate slurry and into the soil at all times
said slurry is in contact with both electrodes. The voltage
potential can be selected to preclude current contributions from
chemical species other than the desired species. The sampler shank
12 and its affixed, insulated electrode 22 are continuously
subjected to both soil and soil slurry leachate abrasion as the
support member 15 draws the soil chemical sensor and agricultural
chemical delivery system 10 through the soil 51.
The sensing system disclosed herein has, in the real and practical
world, two significant advantages: it is very fast acting,
essentially instantaneous; and it is economical to implement. This
system provides means for current sampling during a very short time
period (typically less than a few thousandths of a second) to
determine the resistivity of the combination of the soil
resistivity and leachate slurry resistivity due to extracted,
dissolved electrolytes, one of which is the target material to be
assayed such as nitrate. The resistivity magnitude of the combined
soil and leachate, when measured by applied voltage differential
and current sampling methods, produces in the present invention an
accurate relative measure of nitrate concentration in soils sampled
at an effective time in the crop growth cycle. With shank 12 with
electrode 22 operated at a 3" depth, and with the geometry of the
preferred embodiment, the indicated resistivity is 160 ohm-m at an
average soil nitrate concentration of 100 ppm.
The system just described and the method of using it within the
present invention are deemed novel in every sense. The effects of
additional negatively charged ion species which may occur in the
leachate are ameliorated by our choice of preferred multivalent
electrode materials, i.e., by a compound or alloy containing
dissimilar multivalent materials such as copper for the positively
polarized electrode and iron, the principal constituent of steel,
for the negative electrode of this first technique. In addition,
this electrode 22 specification has a high degree of specificity
for the target nitrate ion which can be further enhanced by
alternate means described herein.
Those skilled in the art will at once recognize that repeatable
resistivity measurements are usually impossible using these simple
electrodes in the conventional laboratory manner in a quiescent
fluid. Such an effect is primarily the result of electode
contamination and if left unchecked will indeed preclude accurate
leachate resistivity measurement. The present invention removes
this difficulty by the elegant expedient of aligning the geometry
of the aforementioned orifice 14 and electrode 22 such that as the
shank moves through the soil, the soil continously scours away
electrochemical reaction products. Thus slurry resistivity is
predictably measured very near time zero, which can be defined as
the instant current begins to flow through the slurry.
At electrode 22, a selected multivalent material, such as a
material containing copper, reacts with dilute nitric acid (nitrate
solution) to yield nitric oxide as the principal product. The cell
reaction occuring at the interface between electrode 22 and the
leachate contained in the saturated path 50 is given by the
equation:
All of the reaction products listed on the right hand side of the
equation are swept away by motion and abrasion from the electrode
interface with the leachate and do not interfere with subsequent
measurements. It is not necessary that electrode 22 be comprised of
copper or an alloy of copper, and it will be recognized by those
skilled in the art that many other materials are possible.
The resistivity sensitivity of a resulting electrode 22 can be
further enhanced by applying a potential differing from the
aforementioned fixed 1.4 to 1.8 volt range. It is advantageous to
employ this mechanism in combination with soil resistivity
measurements to provide both selectivity and sensitivity to nitrate
species.
Referring now to FIG. 3, the desired discrimination effect is
illustrated by two different resistivity responses to a range of
voltage differentials applied to moving electrodes in contact with
the saturated path 50 of FIG. 2. Curve 56 illustrates the
resistivity 58 of a nitrate bearing soil at a series of fixed
voltage differentials. If the applied voltage, in the case of
nitrate, is held fixed at some value within the 1.4 to 1.8 volt
differential range 59, the indicated resistivity will follow the
lower curve. If, however, the voltage range 59 is rapidly and
alternately swept over the range between 1.3 and 1.5 volts, such as
indicated by curve 57, there will be limited time for diffusion of
nitrate to the electrodes. Apparent resistivity 58 will rise in
response to the voltage differential change. This will be
recognized by those skilled in the art as an expected
electrochemical cell response. The choice of electrode material,
preferably copper bearing alloys for electrode 22, will enhance
this difference. In particular, it has been found that a copper
electrode can double the indicated difference, compared to an iron
multivalent electrode. Those skilled in the art will recognize that
a DC voltage bias combined with a small AC component, typically
4000 Hz to accomodate the size and travel speed of electrode 22 in
the preferred embodiment, is a suitable choice for this
technique.
This technique is also useful should certain soil types be
encountered in which an excess of water soluble species other than
nitrate may exist. Under those conditions, the resistivity of the
slurry may be drastically affected by one or more species in
addition to nitrate when using only natural rainwater as a solvent.
By adding an electrolyte, such as a buffered soluble phosphate
solution, to the solvent, a different baseline resistivity response
(dominated by the added soluble phosphate) similar to curve 56 will
exist, and the variable voltage technique described above permits
the resistivity of the nitrate contribution to be determined.
Returning now to FIG. 2, an applicator shank 40 having a shape
generally similar to sampler shank 12 is attached to support member
15 such that applicator shank 40 cuts through the soil following
the sampler shank to about the same depth and in approximate
alignment therewith. At the soil penetrating end of applicator
shank 40 is an orifice 42 through which fertilizer or other
chemical additives may pass out into the soil. Said fertilizer or
other chemical additive is stored in chamber 44 with the flow
therefrom being controlled by flow control valve 46.
The control valve 46, preferably a fast acting type solenoid valve,
may be rapidly opened and closed in response to a modulated output
signal from sensing and control means 31. The sensing and control
means 31 first determines the relative amount of the target
chemical in the soil and the true ground speed of the farm vehicle
by conventional speed detection means 53, preferably a
non-contacting sensor, and then determines the amount of chemical
additive to be applied to reach the level desired. The sensing and
control means 31 then signals the chemical application control
valve 46 to dispense the appropriate amount of fertilizer or other
additive through conduit 42 driven by the pressure from chamber 44,
in the case of anhydrous ammonia, or by additional pump means 48
installed between conduits 47 and 49 in the case of most
agricultural chemicals and into the soil 51.
During equipment use the action is as follows. Support member 15 is
hitched to the rear of a draft vehicle, typically a farm tractor,
and both the ground engaging soil sampler shank 12 and the
applicator shank 40 are lowered so that they penetrate the soil to
a similar depth, preferably between zero and twelve inches. As the
tractor moves in the direction of arrow 13, member 15 is drawn
forward and attached shanks 12 and 40 proceed to slice through the
soil. A tapered or wedge shape of sampler shank 12 will result in a
saturated path 50 which maintains close contact with the sampler
shank as it passes. Protrusion 20 prevents contacting soil from
clogging solvent orifice 14 as solvent 52 is applied to the soil
51. The passing soil is saturated with solvent 52 exiting from
solvent orifice 14 thereby creating a conductive saturated slurry
path 50 as explained earlier. The forward motion of sampler shank
12 now causes the plume of conductive slurry to trail back in
intimate contact with the iron body of shank 12 and ultimately to
bridge the insulating gap between shank 12 (the iron electrode) and
the positive potential electrode 22. A current proportional to the
resistivity of the combination of the slurry and the soil itself
will now flow between the electrodes which, as explained earlier,
have impressed upon them a potential difference or current. Sensing
and control means 31 measures said current passing through the
leachate slurry and soil and therein derives therefrom a measure of
resistivity, used in this example to assay nitrate concentration
therein. The sensing and control means 31 instantly generates the
required signal to drive control valve 46 and thus to dispense the
appropriate amount of fertilizer or other chemical through orifice
42 as said orifice of applicator shank 40 passes adjacent the spot
where the soil was tested but a moment previously.
In the preferred embodiment, soil chemical sensing and the
corresponding application of fertilizer or other additives proceeds
continously as the tractor traverses the field, thus providing a
novel system for localized soil chemical testing and agricultural
chemical application in real time. Indeed, the system 10 of the
present invention provides a many-fold higher density of samplings
per acre than can be cost-effectively provided via more
conventional procedures. In fact, the soil chemical sensor and
agricultural chemical delivery system 10 as reduced to practice
before filing this application can provide up to three thousand
chemical constituent assays per acre, using three of means 12, with
the capability of directly integrated fertilizer and additive
applications at each of the sample assay locations.
Referring now to FIG. 4, which more generally describes the
functions of control means 31, it may be seen that control means 31
is provided with two types of inputs. Preferably, rapidly varying
field operation direct sensory data including soil chemical sensor
data 60 from a plurality of sensors and true ground speed data from
a single, generally non-contacting sensor 61 are measured
electronically. Slowly varying or area sensitive operating
parameters 62 are provided to control means 31 preferably by direct
key entry by an operator or by means of electronic communication
such as digital encoded data or direct analog voltages from
external sources. Control means 31 interprets all sources of these
data in its logic control unit 63, producing a series of chemical
delivery signals 64 that are transmitted 65 to a plurality of
chemical delivery valves and coordinated with the individual soil
chemical sensor measurements made along the path of the sampler and
applicator shanks.
Practical experience has shown that the first requirement of the
sensing and control means is to respond to fluctuations in ground
speed of the tractor. Agricultural chemical flow to each chemical
applicator shank should be directly proportional to the ground
speed of the tractor.
The maximum chemical flow rate from a complete tool assembly is
determined by the equation:
where Q.sub.max equals the maximum chemical flow rate, D equals the
lateral distance between adjacent chemical delivery shanks, and S
equals true ground speed.
Input set point parameters 62 include, when fertilizing with
nitrogen, the desired soil nitrate level as well as a maximum
application rate, and the system 10 measures the nitrate in the
ground during operation. Agronomic practice variables for both the
desired soil nitrate level and maximum application rate are not
expected to be constants over a farm field and may vary for example
depending upon the planting time of the particular crop, the soil
type or moisture holding capacity, or the hybrid variety grown in
the field. These parameters are area-by-area farm production
guidelines and do not fluctuate as widely as local soil chemical
status; consequently, these input set points can either be manually
set as constants or varied between production guidelines
established for field subregions.
By comparing and subtracting the measured nitrate level from the
desired maximum level, the sensing and control means 31 determines
if nitrogen fertilizer needs to be added and adds it in proportion
to the amount of nitrate already present. Because it is in no way
desired to restrict the range of interpretation of the soil
chemical data and the benefits to be derived therefrom, this
interpretation can take the form most appropriate to maximizing
benefits. For example, the classical exponential yield curve is but
one form of theoretical crop response to soil chemical level.
Quadratic and plateau models are also appropriate for benefit
analysis. Alternate functional relationships in response to spatial
nutrient variability may be employed to provide interpretation
criteria for managing end use objectives such as minimizing ground
water contamination and energy waste or maximizing field yield
returns as well as crop quality.
In the preferred embodiment, a local fertilizer application rate
(or sublocal) is set by first subtracting a local soil nitrate
measurement (NO.sub.3.sup.-)local from the control setpoint
(NO.sub.3.sup.-).sub.setpoint. Recommended application rates (for
"zero" soil nitrate contribution or submaximum) are then adjusted
by the ratio of this difference to the control setpoint. In
mathematical form, the equation is: ##EQU1##
In the case of corn with a yield goal of 150 bushels per acre, a
maximum nitrogen fertilizer application of 150 lbs per acre (at
zero soil nitrate) and a maximum soil nitrate level of 120 ppm have
been found to be representative operating parameters.
The actual flow rate of chemical applied by the applicator shank is
then modified by the above equation, so that:
where Q equals the local chemical flow rate, D equals the lateral
distance between adjacent shanks, and S equals the true ground
speed.
The delay between the time the chemical leaves a control valve and
the time it reaches the soil is a prime consideration for precision
application. Referring again to FIG. 2, the length of conduit 45
between control valve 46 and orifice 42 is preferably kept as short
as possible. Time delays result from the time necessary for the
chemical to move to the orifice 42 in the shank 40 from the valve
46. If the nitrate level measured in the soil is high, the required
flow rate will be low and the delay of application of chemical will
be increased relative to soil conditions where the nitrate level is
low. The selection of a minimum length for conduit 45,
approximately 1 foot of 1/4" tubing, ensures that maximum chemical
delivery occurs at the points where the soil is the most deficient
in soil chemical level and, accordingly, contributes the greatest
incremental yield benefit and application precision.
In operation, it has proven beneficial to time "average" soil
chemical sensor readings for interpretation by conventional
agronomic practice and produce time-averaged flow conditions. Even
this less site-specific averaging is superior to known systems that
experience long activation time delays by not even responding to
ground speed changes in less than 10-20 seconds.
Parallel readings may be averaged together also as a means of
determining, at the same point in time, the soil nitrate used for
the computation of chemical flow requirements. This process
provides a truly representative sample for an area and is useful
for comparison to conventionally derived soil chemical estimates
for a soil region.
Referring again to FIG. 2, in practice it has been found that the
preferred embodiment produces an averaged resistivity signal that
is 10 to 30% lower than the anticipated correlation of nitrate with
resistivity. This effect is due to the small contribution of soil
particle resistivity to total slurry resistivity at saturation.
Calibration to eliminate this small error may be accomplished in
several ways, one of which is to utilize the solvent flow
capabilities of valve 23. Solvent flow, while the farm vehicle is
moving, is suspended for a fraction of a second. The resulting
resistivity determined is the contribution from the in situ soil
particles. By instantaneously subtracting the reciprocal of the
resistivity obtained with the slurry from the reciprocal of the
resistivity obtained with no slurry in contact with the soil, an
error correction can be made. Alternatively, the solvent flow may
be uninterrupted and simply rapidly directed away from the path of
the sensors and back again.
In practice, the preferred embodiment has proven beneficial without
use of the described calibration feature. We have observed a
correlation between soil nitrate level and indicated resistivity.
Correlation rather than direct infield calibration has proven to be
a satisfactory practical solution.
Alternatively, calibration for the same soil particle error can be
effected by operating the system through a portion of a farm field
and observing the indicated soil nutrient display on control means
31. The average observed reading may then be compared to a rapid
colorimetric field test of soil samples obtained from the same
portion of the field in which the soil chemical sensor and
precision chemical application system was operated.
With this procedure, approximately 483/4" diameter soil cores to
12" depth are preferably taken and thoroughly mixed with a gallon
of distilled water in a rubber bucket, the resulting slurry
filtered and the extract tested using a minimum of three EM
Quant.RTM. No. 10020-1 nitrate test strips, available from EM
Science, Cherry Hill, N.J., which are then read in a Nitracheck.TM.
colorimetric strip reader, available from Medistron Ltd., Horsham,
West Sussex, England. The resulting indicated nitrate reading from
the display on control means 31 may then be scaled to agree with
the averaged output of the three or more test strips.
By employing any of these or other calibration techniques, the
previously described small error in the averaged resistivity signal
may be reduced to an extremely small error; i.e., fertilizer or
other agri-chemicals may be applied with extreme precision.
Other alternate forms of the present invention will suggest
themselves from a consideration of the apparatus and practices
hereinbefore disclosed. Accordingly, it should be clearly
understood that the systems and techniques described in the
foregoing explanations and depicted in the foregoing drawings are
intended as exemplary embodiments of the invention and not as
limitations thereto.
* * * * *