WO2000015987A1 - Irrigation system having sensor arrays for field mapping - Google Patents

Abstract

A novel process and apparatus for selectively or simultaneously mapping field or crop properties, or applying irrigation water and/or agricultural chemicals are disclosed. The apparatus is an improved field traversing irrigation system having a plurality of sensors (15) mounted thereon for measuring in one or more field or crop properties or conditions across the area of the field traversed by the system (10). The data from the sensors (15) is then transmitted to a microprocessor (16) included in the apparatus which is capable of generating spatial maps of the measured properties across the field. These maps may be used to identify variations in properties across the field, to determine the field-wide need for application of irrigation water or agricultural chemicals, or to target specific zones or hot spots in need of selective treatment. Commencement of application may be effected manually, or it may be controlled automatically by the microprocessor (16) in response to any determined need. Furthermore, application may be conducted field-wide or selectively to the identified target zones.

Description

IRRIGATION SYSTEM HAVING SENSOR ARRAYS FOR FIELD MAPPING

Background of the Invention Field of the Invention

The invention relates to a field traversing irrigation system having an array of sensors mounted thereon for measuring and mapping field or crop properties.

Description of the Prior Art

Many management operations in agricultural systems involve uniform application of inputs (water, fertilizer, pesticide) over the entire management unit or field. Spatial variation within a management unit can be significant and uniform applications can result in waste and/or impairment of the plant . Recent concerns relating to environmental quality have resulted in increased interest in matching inputs to specific areas in order to limit contamination of the environment . In order to more accurately apply inputs within variable systems, knowledge of the distribution and content of field anomalies is essential. Anomalies in crop fields can be categorized with respect to either the source of the variation or in terms of the manner in which the anomaly is expressed. Sources for field variation include biology, soil heterogeneity, and management practices. Biological factors include genetic variation that causes differences in the plant development, non-uniform insect infestations, and plant pathogens that do not uniformly infect the crop. Soil heterogeneity results from variation in hydraulic, physical and chemical properties and is variable on a scale ranging from a few centimeters to hundreds of meters. A particular field may include multiple soil types, each with unique characteristics such as texture, pH, and depth to an impeding layer. Finally, management practices can induce anomalies through equipment malfunctions or operator errors. In addition, there is an interaction between these factors. For example, uniform irrigation may minimize the impact of soil variation, while providing an adequate supply to one area and an excess in another area.

A second classification of crop anomalies based on how the anomaly is expressed is appropriate. Plant density changes including reduction in the number of plants per unit land area as well as the absence of plants is one expression of an anomaly. Anomalies may also express as changes in plant architecture such as plant height, leaf area per plant, and leaf orientation. More subtle anomalies will express as changes in plant appearance such as visible color and reflectance or emission of electromagnetic radiation in specific wave lengths. Finally chemical emissions from plants are associated with certain anomalies. For example, many plant stresses induce the emission of ethylene.

Methods for detecting anomalies include: visual inspection, reflectance or emission of electromagnetic radiation, and measurement of chemical vapors . Visual inspection by an expert observer is the most common method for anomaly identification, though its utility is dependent upon expert knowledge and on site expertise. Electromagnetic radiation is a powerful and widely used approach to anomaly identification that can be implemented on various levels ranging from field based observers to orbital satellites . Electromagnetic radiation sensing and analysis are not dependent upon an on site observer and thus can be remotely monitored and analyzed.

Irrigation control strategies have been described for use with field traversing irrigation devices such as center pivot irrigation systems, linear move or side roll irrigation systems, and wheel line irrigation systems. For example, Wolfe, Jr. (U.S. patent 4,662,563) disclosed a center pivot irrigation system utilizing one or more soil moisture sensors dispersed in the field which are in communication with a central controller. More recently, McCann et al . (U.S. patent 5,246,164, the contents of which are incorporated by reference herein) disclosed a field traversing irrigation system having independently controlled valves allowing selective irrigation of hot spots or zones of the field rather than uniformly irrigating the entire field. Spatial data indicative of field or crop conditions is collected and input into a central microprocessor to generate maps identifying zones requiring irrigation. The microprocessor then determines the position of each sprinkler assembly, compares this position with the irrigation requirements for the field, and generates appropriate control codes for each individual sprinkler assembly. Despite these recent advances, there is a continuing need for improved automated control of irrigation systems which identifies variations in field and/or crop conditions and allows selective and variable application of water and/or chemicals to areas of need.

Summary of the Invention We have now invented a novel process and apparatus for selectively or simultaneously mapping field or crop properties, or applying irrigation water and/or agricultural chemicals. The apparatus is an improved field traversing irrigation system having a plurality of sensors mounted thereon for measuring one or more field or crop properties or conditions across the area of the field traversed by the system. The data from the sensors is then transmitted to a microprocessor included in the apparatus which is capable of generating spatial maps of the measured properties across the field. These maps may be used to identify variations in properties across the field, to determine the field-wide need for application of irrigation water or agricultural chemicals, or to target specific zones or hot spots in need of selective treatment. Commencement of application may be effected manually, or it may be controlled automatically by the microprocessor in response to any determined need. Furthermore, application may be conducted field-wide or selectively to the identified target zones .

The apparatus of this invention includes a field traversing irrigation system having a sprinkler boom with a plurality of sprinkler assemblies mounted thereon, and a plurality of movable supports for supporting the sprinkler boom and which are capable of moving over the field. Water and/or agricultural chemicals for spraying the field and/or crops are distributed to each of the sprinkler assemblies through the boom. A plurality of the sensors for measuring the field or crop properties are mounted in an array along the length of the irrigation system, upon either or both of the sprinkler boom or the movable supports. The apparatus further includes a microprocessor in communication with the sensors for generating one or more maps showing the variance of the measured properties across the field.

In accordance with this invention, it is an object to provide an apparatus and method for generating maps of field or crop properties.

It is another object of this invention to provide a method and apparatus for measuring the variation in field or crop properties across the area traversed by a field traversing irrigation system.

Yet another object of this invention to provide an apparatus and method for managing irrigation of plants with reduced application of water and agricultural chemicals .

Other objects and advantages of this invention will become readily apparent from the ensuing disclosure. Description of the Figures

Fig. 1 is a perspective view of a center pivot irrigation system of this invention.

Fig. 2 shows a flow chart of the irrigation scheduling procedure described in Example 1.

Fig. 3 shows the mounting of the IRT's on the irrigation system.

Fig. 4 shows the location and spacing of the IRT's on the irrigation system.

Fig. 5 shows the mounting of an electronic compass and microprocessor on the irrigation system.

Fig. 6 shows the maximum, minimum, and mean daily air temperatures (mean = solid line) for the experimental site during the test year.

Fig. 7 shows the rainfall and irrigation events (solid and open bars, respectively) for the experimental site during the test year.

Detailed Description of the Invention The process and apparatus of this invention may be used for the application of water and/or agricultural chemicals to a variety of plants, particularly agronomically important field crops, vegetables, fruits, turf grass, and horticultural crops. Without being limited thereto, examples of plants which may be managed using this invention include cotton, corn, wheat, beans, soybeans, peppers, cucumbers, tomatoes, potatoes, roses, and petunias. Examples of agricultural chemicals which may be applied include but are not limited to liquid formulations of pesticides, herbicides, insecticides, fungicides, and fertilizers.

The apparatus of this invention encompasses field traversing irrigation systems, including but not limited to center pivot irrigation systems, linear move or side roll irrigation systems, and wheel line irrigation systems . Figure 1 shows a preferred embodiment of the apparatus utilizing a center pivot irrigation system 1. The center pivot irrigation system 1 generally includes an approximately horizontal sprinkler boom, header, or pipe 10, which is pivotally attached at one end thereof to a stationary central tower 11. The sprinkler boom 10 is supported by a plurality of movable towers or supports 12 positioned along its length, enabling the boom 10 to traverse the field as it rotates about the central tower 11. A plurality of sprinkler assemblies 13 are mounted along the length of the sprinkler boom 10. The sprinkler boom 10 is also connected to a main supply line at the central tower 11 through a rotatable coupling (not shown) for delivering water and/or agricultural chemicals under pressure to each of the sprinkler assemblies 13. Chemicals may be delivered from a separate reservoir and injected into the water flow at the main supply line or the sprinkler boom 10. Water and chemical flow rates may be independently controlled by one or more valves located on the main supply line, sprinkler boom 10, or the chemical reservoir.

Movable supports 12 typically include electronically controlled motors 14 for continuously or intermittently driving the sprinkler boom 10 across the field. Mobilization of the movable supports 12 causes sprinkler boom 10 to rotate across the field. Irrigation water and/or chemicals are concurrently delivered through the main supply line to sprinkler assemblies 13 , which spray the fluid material onto the field and/or crops below their path.

A plurality of the above-mentioned sensors 15 for measuring the field or crop properties are mounted in a fixed array along the length of the irrigation system, usually upon either or both of the sprinkler boom arm 10 or the movable supports 12. The apparatus further includes a microprocessor 16 provided in communication with the sensors 15 for generating one or more maps showing a spatial representation of the measured data, and thus the variance of the measured properties, across the field.

For use herein, sensors 15 should be effective for measuring one or more parameters which are indicative of the condition of the soil, crop, or atmosphere in the immediate vicinity of the soil or crop. Preferred sensors are effective for measuring reflected or emitted electromagnetic radiation, or chemical vapors released by plants, animals or insects. Without being limited thereto, examples of sensors which are suitable for use herein include non-contact surface temperature sensors such as infrared thermometers, leaf N content sensors, leaf color sensors, soil organic matter sensors, and chemical vapor sensors such as insect pheromone sensors and ethylene sensors for detecting ethylene released by plants or animals. Infrared thermometers, including infra-red thermocouples (IRTs) , for measuring plant canopy or soil temperature are particularly preferred.

The number and spacing of the sensors 15 along the irrigation system is variable but should be sufficient to provide an accurate representation of the variation of the measured properties across the field traversed by the irrigation system. Although it is not necessary that the sensors be spaced such that the entire area of the traversed field is within the field of measurement of the sensors, the spacing should be sufficient to detect the anomalies (that is, the areas of variation in the field or crop condition or property) which are of the size of interest. In other words, the sensors should be spaced so that any anomaly or area of variation of this size would be viewed by at least one sensor.

In accordance with one embodiment where the grower desires to differentially treat detected anomalies as described hereinbelow, this spacing of the sensors may also be dependent upon the scale of the smallest individual management unit of interest . A management unit is defined herein as the smallest width of land traversed by the irrigation system (parallel to the boom 10) that the grower desires to differentially treat. For practical purposes, the management unit cannot be less than the smallest width of field that can be differentially treated by the available equipment. Thus, the sensors should be spaced such that any management unit of the desired size should also be viewed by at least one sensor. In this embodiment, the size of the management unit and the width of the anomaly (if described as a square) will generally be the same; detecting smaller anomalies will be of no practical value if those anomalies cannot be differentially treated. However, even if a grower desires to detect and then treat a very small anomaly or management unit, they may be limited by the capacity of their equipment . Typically, with currently available commercial equipment the management unit will be approximately 104 ft width (one side of a 1/4 acre square) . Using field traversing irrigation systems, it is understood that significantly smaller anomalies and management units may be treated, for example, by increasing the number of sprinkler assemblies 13 on boom 10 while reducing their field of application (reducing overlap of application by different assemblies) .

Without being limited thereto, the sensor spacing is preferably approximately equal to the width of the anomaly of interest when the anomaly is described as a square. By way of example, if the size of the smallest anomaly desired to be detected is 1/4 acre square (104 ft by 104 ft, corresponding to a management unit of 104 ft) , then the sensors should be spaced no more than about 104 ft along the length of the system to allow a square anomaly of this size to be detected. However, the sensors' field of view should also be considered in determining spacing. Sensor spacing may be increased by a distance up to half the field of view without loss in ability to detect anomalies or variations on field or crop conditions. In practice, we have determined that spacing the sensors such that about 5% or more of the land area traversed by the irrigation system (measured at soil level) will allow detection of most anomalies. Depending upon the specific sensor used, the skilled practitioner will recognize that this percentage may decrease with increasing crop height if the sensors' height and field of measurement remain unchanged. Generally, there should be at least one sensor per tower. In the preferred embodiment sensors should be spaced less than or equal to about 150 ft apart, particularly less than or equal to about 100 ft.

To correlate the position of the sensors with each set of measurements, at least one additional detector 17 is also provided to determine the angular position of the sprinkler boom 10 as the irrigation system traverses the field. A variety of position detectors are suitable for use herein, and include, but are not limited to electronic compasses, global position satellite (GPS) detectors, or mechanical resolvers as are conventional in center pivot irrigation systems. Resolvers are described, for example, by Unruh et al . (U.S. patent no. 4,626,984, the contents of which are incorporated by reference herein) . The output of the position detector is also in communication with the microprocessor 16 such that the measurements from sensors 15 may be correlated with the corresponding location on the field.

Microprocessor 16 is a microprocessor based computer control unit having conventional interface hardware for receiving and interpreting signals from the sensors 15 and position detector 17. The microprocessor is provided with mapping software for generating one or more maps showing a spatial representation of the measured data or properties across the area of the field traversed by the irrigation system. A variety of commercially available mapping software programs are suitable for use herein. Without being limited thereto, examples of mapping software which may be used include TRANSFORM 2D (previously known as SPYGLASS TRANSFORM; available from Fortner Research, Sterling, VA) , ARCVIEW (Environmental Systems Research Institute, Inc., Redland, CA) , ENVI (Research Systems Inc., Boulder, CO), and TNTMIPS (Microimages, Lincoln, NE) .

In a preferred embodiment, microprocessor 16 may be in communication with an optional monitor 18 and/or recording instrument 19, such as a printer, for presenting a display of the generated map. The irrigation system may also include sensors 20 for ensuring proper alignment of the supports 12 as is conventional in the art . Electronically controlled motors 14 are independently responsive to these alignment sensors 20 for maintaining the sprinkler boom 10 in an approximately linear configuration. Examples of alignment sensors which are suitable for use herein include but are not limited to those described by Kegel (U.S. patent no. 4,580,731), Schram (U.S. patent no. 4,397,421), and Hunter (U.S. patent no. 4,149,570).

Maps generated by the apparatus may be used to monitor field or crop conditions, or control the amount of water and/or agricultural chemicals applied to the entire field or to any particular zone of the field traversed by the irrigation system. Control of water or chemical application may be effected automatically or manually. For instance, the grower may identify target areas in need of treatment by simple visual examination of the maps; the entire system or selected sprinkler assemblies may then be activated as needed.

In another preferred embodiment, the irrigation system may be adapted to automatically control the application of variable amounts of water and/or chemicals to the entire field, or to only selected target areas of the field identified as needing treatment from the generated maps . Techniques and irrigation systems for microprocessor controlled selective application of water and/or chemicals in this manner have been previously disclosed by McCann and Stark (U.S. patent no. 5,246,164, the contents of which are incorporated by reference herein) and are suitable for use in this invention. In accordance with this embodiment, each sprinkler assembly 13 may be provided with an optional controller or servo in communication with the microprocessor 16 for selectively opening and controlling the rate of flow there through. Controllers or servos may also be provided in combination with cooperating valves located on the main supply line, sprinkler boom

10, or chemical reservoir, for controlling flow of water and/or chemicals upstream of the sprinkler assemblies 13.

Using the generated maps, microprocessor 16 determines the specific water or chemical needs for different regions of the field, identifying any target area requiring treatment. Microprocessor 16 determines the current position of the system relative to the generated map and initiates control signals or codes for activating the appropriate sprinkler assemblies passing over these target regions, as described by McCann and Stark (ibid) . In this embodiment, microprocessor 16 may also control the motors 14 of each support 12 to control the speed and residence time of the irrigation system over any particular area or radial (angular) location of the field.

In operation, the irrigation system may traverse the field and collect measurements for generating maps either continuously or intermittently. However, in the preferred embodiment, measurements are collected at predetermined intervals as the system traverses the field, usually between about every 0.5 to 5° of rotation of the sprinkler header arm 10 about the center pivot

11. It is understood that the interval is not critical, and that intervals other than 0.5 to 5° may be used. The actual interval selected may vary with the condition being measured and the level of precision desired. Moreover, it is also understood that at any particular angular frequency, the spacing between measurements increases toward the distal end of the boom 10. Thus spacing of the measurements by different sensors 15 (along arcs of different radii) will differ.

While the invention has been particularly described for use with center pivot irrigation systems, it is understood that the sensors may be similarly mounted upon other field traversing irrigation systems, such as linear move or side roll irrigation systems, or wheel line irrigation systems. Any of these systems may be readily adapted for generating maps of field or crop properties as described herein.

The following examples are intended only to further illustrate the invention and are not intended to limit the scope of the invention which is defined by the claims .

Example 1 Temperature maps were generated by detecting emitted radiation in the thermal range (8-14 μm) using an array of infrared thermometers mounted on a center pivot irrigation system.

Materials and Methods Experimental site

This work was conducted during one growing season in a 16 acre field located in Lubbock, Texas. The primary soil is an Acuff loam (fine-loamy, mixed, thermic, Aridic Paleustolls) which is a deep, nearly level to gently sloping, moderately permeable loamy soil. There are likely inclusions of Amarillo loamy fine sand (fine-loamy, mixed, thermic, Aridic Paleustalfs) too small to be included at the mapping scale. In the previous year, the field had been used for small plot irrigation studies involving forage grasses . Several anomalies induced by the previous research exist in the field, including areas where herbicide residues reduced plant growth, areas where residual herbicide prevented plant growth, and areas affected by vehicle traffic.

Irrigation System

A three tower Valley Irrigation center pivot irrigation system (Valmont Industries, Inc., Valley, NE) equipped for LEPA irrigation was used in this research. The pivot is 477' in total length, with 146' between towers and a 42' overhang. Drops are spaced at 80" and include a manual shutoff valve and a 6 psi pressure regulator at each drop. The system was nozzled for 450 gpm water supply which was regulated at the well head to provide a pressure at the center pivot of 20 psi. Initial irrigation was applied using a spray pad located 24" above the soil surface, wetting the entire surface. Drag socks were added after crop establishment and water was applied directly to the soil surface in alternate furrows .

High speed motors were installed on the center pivot on August 14 (day of year 226) , reducing the minimum revolution time from about 8 hours to about 4 hours. On October 19 (day of year 290) higher speed motors were installed, further reducing the minimum revolution time to slightly more than 2 hours .

Cultural Practices

The field was tandem disked and then seedbeds were shaped on April 12. The seedbeds were further shaped using a rolling cultivator in early May. A total of 9 cm (3.5 in) of water was applied between April 24 and May 3 in five separate events. Cotton (Paymaster HS26) was planted on June 1 immediately following rodweeding the seedbeds . Preemergent herbicides (Dual and Caporal) were sprayed over the beds on June 2. Three irrigations totaling 3.6 cm (1.4 in) were applied between June 3 and June 14. The field was cultivated and furrow dikes were installed on June 30 and again on July 6.

On June 21 a weather station was installed at the site to monitor air temperature, global and net radiation, wind speed, relative humidity, and rainfall. Observations were recorded once per minute and 30 minute averages were stored and graphically analyzed, daily. All data was collected using a Campbell Scientific CR21X dataloger.

Irrigation Management

Beginning on July 7, irrigation was managed using the BIOTIC irrigation scheduling procedure of Upchurch et al . (U.S. patent no. 5,539,637, the contents of which are incorporated by reference herein) . This irrigation management was independent of the generation of temperature maps described hereinbelow. A single, fixed position, infrared thermometer (IRT) was located approximately 20 m south east of the pivot point. This IRT was mounted with a nadir view of the crop, directly above a plant row. Its height was adjusted periodically to insure that the field of view was filled with foliage. The Campbell Scientific CR21X dataloger used for the environmental measurements described above was used to log the canopy temperature and provide an irrigation signal .

A flow chart of the irrigation scheduling procedure is shown in figure 2. An irrigation signal was given if the following conditions were met: 1) canopy temperature was above 28°C for at least 275 minutes, 2) less than 17 mm of rainfall occurred since the last irrigation, and 3) at least 3 days had elapsed since the previous irrigation. Time above 28°C was set to zero at midnight each night. If 21 mm of rainfall was recorded it was considered an irrigation event and the appropriate counter was reset . Twenty-one mm of irrigation water was applied at night on the days that the above conditions were met .

Canopy Temperature Measurements

Canopy temperature was measured using 10 infrared thermocouples (IRT's) mounted on the center pivot. The mounting system used is shown in figure 3. The IRT ' s were located 2 m above the soil surface, angled at 45° from vertical and oriented 90° to the center pivot overhead pipe. The field of view of the IRT's is approximately 30°. Therefore, at the soil surface, the IRT's viewed an elliptical spot 1.5 m by 2.3 m, centered 2 m in front of the center pivot . As the plant canopy height increased the spot size was reduced.

The location of the IRT's along the center pivot is shown in figure . The relative spot size viewed by the IRT' s is shown by the ovals in this figure . Given a 2 m mounting height and this spot size, approximately 10% of the total area under the pivot was viewed as the system rotated. This area was reduced linearly as the canopy height increased, such that with a i canopy height only 5% of the total area was viewed by the IRT's.

An electronic compass was attached to the center pivot as shown in figure 5. The compass produced a voltage proportional to its angle with respect to magnetic north, providing an indication of the angle of the center pivot. Any time the angle of the center pivot changed by more than 0.5°, the temperature from each IRT was recorded and stored. This provided between 700 and 720 points from each full rotation of the center pivot. Because the angle of the pivot and the sampling frequency of the dataloger were not synchronized, the system generally collected less than 720 points during a rotation. A second Campbell Scientific CR21X was used to monitor the output of the IRT's. A solar panel was attached to the top of the center pivot above the dataloger and connected to two 12 V marine batteries, connected in parallel, providing power for the dataloger and associated equipment .

The electronic compass was mounted on an extension from the middle tower of the three tower pivot . The mounting arm was stabilized with guy wires to minimize the effect of wind and vibrations on the measured angle. In addition, the output from the compass was electronically filtered to correct for vibrations induced during movement of the center pivot . It was necessary to extend the compass mount approximately 2 feet beyond the wheel of the pivot to eliminate electromagnetic interference from the drive motor and overhead wiring.

Canopy Temperature Observations and Processing

At frequent intervals the center pivot was rotated at full speed, without applying water, to collect data for mapping the canopy temperature over the entire field. In addition, observations were recorded each time irrigation water was applied. Table 1 contains a list of the dates when the system was rotated and the number of rotations completed during each 24 hour period.

The results were processed through several computer programs to prepare the data required for generating the temperature maps . The processing steps are:

1) Data was collected from the CR21X and transferred to comma delimited ASCII file format using Campbell Scientific 's PC208 software (Campbell Scientific, Logan, Utah) .

2) These data files were split into single day of year files and a header line was added to identify each column of data. This editing was completed using a basic text editing program on a Macintosh computer. Each file contained all data collected from midnight to midnight for a particular calendar date.

3) The files for each day were imported to a graphics program (KALEIDOGRAPH, Synergy Software, Reading, PA) and a series of operations were completed to: a) convert time to hours since midnight, b) correct the compass readings for the effect of the center pivot on the measured angle, and convert angle to radian's, c) prepare a line graph showing the information about the number, direction, and speed of rotations, and d) convert the data for each rotation to a matrix format as shown below:

θ ; T 1,1 T 2,1 T 3,1 T ιo,ι Ci Tai C3 ti θ ₂ T 1,2 T2.2 T3.2 T 10,2 Cl Td2 C3 t2 θ i T 1,3 T2.3 T 3,3 T 10,3 Cl Td3 C3 t3

θ n T l,_n T 2,n ,n lO. Cl Ta„ C3 tn

where θ_± is the angle of the pivot, d is the distance from the center of the circle to IRT I, c_L are constants (distances) used to separate the air temperatures from canopy temperatures in the maps, T_i#j are the canopy temperature from IRT I at angle j , Ta_£ are air temperatures measured at the same time as the canopy temperatures, and t_± is the time of day the data was collected for each row in the matrix. A separate matrix was prepared for each rotation of the center pivot during a given day. If a particular scan spanned two days, the data was combined to produce a single matrix.

4) The matrix was then imported into an image analysis program (originally available as SPYGLASS TRANSFORM, now available as TRANSFORM 2D; Fortner Research, Sterling, VA) and transposed.

5) An image was produced for each rotation of the center pivot using a polar image generating routine included with the software .

6) If multiple scans were available for a given day of year, the data were linearly interpolated to exactly 0.5° angle increments . No interpolation was done in the radial direction. These matrices were then averaged, cell by cell, to produce a new matrix of equal dimension, and an image was prepared using the polar routine.

File size for the data collected each day depends on the number of rotations completed. As an example, on DOY 231, three complete rotations and approximately Vz of an irrigation cycle are included, producing a 221.3 kbyte file. After processing the data into individual scans, each file is 55.4 kbytes.

Existing Anomalies

Several areas of this field were affected by residual herbicide applied prior to the installation of the center pivot. A long lasting herbicide (Hi-Var-X) had been applied to fence rows. All plants in these areas were killed, providing easily identified anomalies of various sizes, shapes, and orientation with respect to the IRT's. Other areas of the field were affected by lower concentrations of residual herbicide that reduced plant population and vigor. Although these were not as easily delineated visually, the effect could be seen. Two areas in the field were infested with Bind weed and Nutsedge. These areas were not planted to avoid distributing the weed problem to larger portions of the field. Finally, a highly eroded roadway was refilled and leveled when the pivot was installed. Plants in this area appeared to grow more vigorously. With the exception of the weedy areas, these anomalies were essentially narrow strips running in several directions across the field.

Irrigation Treatments

At two growth stages, irrigation was withheld from zones of the field to induce water stress . These treatments were replicated three times as 10° wide wedges, located to avoid the herbicide induced anomalies . Prior to canopy closure water was withheld from three zones, 20-30°, 120-130°, and 270-280° measured from magnetic north. Water was withheld from this treatment beginning on July 7 (DOY 205) and normal irrigation was resumed on August 28 (DOY 240) . A second treatment was imposed after the canopies from adjacent rows visibly overlapped. There were three replicates of this treatment at 80-90°, 200-210°, and 310-320° measured from magnetic north. Water was withheld from this treatment beginning on August 18 (DOY 230) . To avoid surface flow of water from the irrigated areas into the treatment zones, water flow from the well was stopped 1° before the treatment area and the center pivot was stopped for 150 seconds to allow water to drain from the system before it was moved across the treatment area. In addition, dams were built in each furrow on both edges of all treatment areas . The center pivot irrigation system produced wedge-shaped patterns of water stress in the water deficit treatments. At the first planted row the water deficit area was 7.4 feet (2.3 m) wide and at the distal end of the pivot the width was 84.1 feet (25 m) . At the first IRT the width was 17.4 feet (5.3 m) and at the last IRT it was 73.2 feet (22.3 m) . Subsurface lateral movement of water reduced the effective width of the stressed areas. At the first planted row there was no visible effect on plants, and at the first IRT the visibly stressed area was approximately 3 feet (1 m) wide.

Results and Discussion

The daily maximum, minimum and average air temperatures are shown in figure 6. The average daily temperature during the test year was approximately 2°C higher than the previous two years.

Rainfall and irrigation events are shown in figure 7. Five preplant irrigations were applied between DOY 114 and 124, for a total of 90 mm. The first irrigation scheduled using BIOTIC occurred on DOY 189. An irrigation signal occurred and water was applied every three days until DOY 201. Irrigation that might have occurred on this date was delayed for two additional days because of a 22 mm rainfall event on DOY 199 which was sufficient to reset the irrigation counter in the data logger. No irrigation was applied between DOY 209 and 220, as a result of low air temperature and three rainfall events . Irrigation was applied every three to six days between DOY 220 and 244. Air temperatures began to decline after DOY 244 and no further irrigation signals occurred.

Total applied irrigation for the season was 373 mm, with 90 mm applied preplant. Total rainfall during the growing season was 104 mm. This provided 387 mm (15.2") from irrigation and rainfall between planting and harvest. BIOTIC scheduling resulted in 14 irrigations during the season. Dropping air temperatures and rainfall resulted in no irrigation applications after DOY 244.

Periodic calibration checks were made on the IRT's used in this project. With a few exceptions, the IRT's remained within the specifications published by the manufacturer. Deviation of the IRT output from the calibration standard never indicated a systematic degradation of the instrument ' s performance . All error appeared to be random with an average value of 0.3°C. Anytime a particular IRT deviated from the calibration standard by more than 0.5°C, it was cleaned and retested.

At the end of the growing season the IRT's were removed, the calibration was checked in the laboratory, and they were inspected under a stereo-microscope . A water insoluble deposit was noted on the lens of all IRT's. However, after removing this deposit with a metal polishing compound, all IRT's agreed with the calibration standard within their published specifications . The origin of the deposit is not known.

In temperature maps produced with this apparatus, distinct rings can be seen. Progressing from the inside of the circle, the first 10 rings are the observations from the IRT's and the outside ring is the air temperature . Each figure involves both position in the field and time of day. Generally, the system was rotated clockwise starting from 3 degrees East of North, which is the top of all figures. The width of each ring is controlled by the distance between the IRT's, therefore the rings are not a uniform width. The color scale shown at the bottom of each figure was chosen to enhance the detection of known anomalies in that particular figure, and are not the same for all figures.

With respect to one thermal map made prior to full canopy closure and completed one day before an irrigation, data collection occurred between 1000 and 1800 and irrigation began at approximately 1830. Most of the existing anomalies can be identified, including the North and South turn rows, and the bare fence rows in the South-East quadrant of the field. Although not distinct, the bare area in the North-East quadrant is visible as a slightly warmer area. Because air temperature and radiation varied during the observation period a gradual heating of the surface is apparent as the center pivot was rotated clockwise, with relative low temperatures (30-35°C) in the North-East quadrant, and high temperatures (greater than 45°C) in the entire West half of the field.

Irrigation was applied during the evening of DOY 208 and the canopy temperature mapped again on DOY 209. A map for DOY 209, which used the same temperature scale used in the previously described mat, demonstrated the large decrease in canopy temperature following irrigation. Existing anomalies, including turn rows and bare fence rows, could be identified in this map, even with the substantially lower surface temperatures. The entire soil surface of the South turn row was wet as a result of the irrigation resulting in a surface temperature lower than the surrounding area. Temperature of the North turn row was collected later in the day, as the center pivot was rotated, allowing time for the soil surface to dry resulting in higher temperatures . In addition to the existing anomalies, the areas where water was withheld can be identified in this figure. The treatment zones at 20-30° and 120-130° have distinct warm areas at the outer edge of the pivot, while the zone at 270-280° is above the surrounding area the full length of the pivot, with the exception of the area viewed by the first IRT. This suggests that small areas with anomalous temperatures will be most distinct when the energy load is large . This data was collected after the treatment areas had missed only one irrigation on DOY 205. Therefore the difference in applied water detected by this thermal map was only 0.5". Canopy temperatures were mapped on DOY 213 following rain and during cloudy sky conditions . Air temperature remained between 18 and 20°C throughout the day. Surface temperatures throughout the field were between 18 and 20°C and all surfaces were visibly wet . Although not as distinct as in previous maps , the turn rows and bare fence rows could be identified, being slightly warmer than surrounding areas . The temperature difference between these anomalies and the surrounding areas was approximately 0.25°C. Small differences in the calibration of individual IRT's are apparent in this figure as rings. Although all IRT's were functioning within the manufacturers published specifications, these results demonstrate the importance of rigorous cross calibration of multiple IRT's.

On DOY 231 three canopy temperature maps were collected between 0900 and 2000. All anomalies could be identified in each of the maps, including the areas where water had been withheld. Intermittent cloud cover during the day produced striations in the temperature maps . Cloud induced reductions in radiation resulted in transient changes in scene temperature that appear as striations in the thermal map.

Data collected between 2200 on DOY 236 and 2300 on DOY 237 was averaged to produce another map, using 6 full rotations of the pivot. This produced a more detailed map of the canopy temperature anomalies than single scans . Higher temperatures in the water deficit treatments can be seen for all ten IRT's. The inner most IRT viewed a treatment area that was approximately 1 meter wide, 1/3 the wide of the IRT's field of view. The East side of the field appears to be approximately 2°C cooler than the West side, on average.

Plant growth on the West side of the field was reduced by previous herbicide applications, resulting in a lower plant population and therefore a lower canopy density. It is possible that the lower canopy density allowed the soil surface to be included in the IRT's field of view, resulting in the higher temperatures. Additionally, gaps in the canopy would increase the evaporative demand as a result of increased air flow around the plants and reflection of incoming radiation from the soil surface. Since the IRT ' s were mounted such that only openings in the canopy larger than 0.9 m would be included in the field of view, it is probable, that the increased temperatures observed on the West side of the field are an indication of water stress.

Conclusions

Center pivot mounted IRT ' s were used to map the canopy temperature of a cotton crop as the pivot was rotated through the field. Areas that were not planted were apparent in the temperature maps, generally displaying temperatures higher than the surrounding plant canopy. Differences in observed temperature as small as 0.25°C could be identified using this method. Areas of the field where water was withheld were apparent in the temperature maps within 3 days of the first differential application.

The time of day when the temperature was measured impacted the ability of this procedure to detect anomalies . The anomalies were most apparent during daylight hours because the temperature difference was large. However, in some cases the water stressed plants and bare soil could be detected in maps collected at night .

Intermittent cloud cover caused striations in the maps that interfered with the detection of temperature anomalies . Visual inspection of several maps collected during intermittent cloud cover overcame this effect .

The IRT's used in this study functioned reliably throughout the growing season. However, inspection after the season revealed a water insoluble deposit on the lens . Although this deposit must have occurred during the growing season, routine calibration tests established that the IRT's performed within the published specifications for the duration of the study.

Positioning of the IRT's along the center pivot allowed detection of all of the anomalies in the East side of the field. The abandoned road and fence lines in the West side of the field were oriented tangential to the path of the IRT's. The arrangement of a limited number of IRT's along the center pivot prevented full coverage of the field. Therefore these areas were not well defined in the temperature maps . This result suggests that the geometry of the anomaly and the infrared thermometer array interact in a complex manner that may be exploited to enhance anomaly detection.

This mapping procedure clearly defined the zones where water was withheld. The width of treatment areas varied from approximately 2.3 m to 25 m, with the effective treatment area being between 1 m and 20 m, based on plant size. The 1 m wide zones near the center of the field were apparent in the temperature maps, establishing the potential to resolve anomalies smaller than the field of view of the IRT.

Multiple, high speed scans of a field within a single day using this procedure will likely increase the usefulness of the temperature maps by reducing the impact of ambient environmental conditions . Thermal images collected in a very short time interval will probably give a sharper distinction of the anomalies and perhaps even detect more subtle ones . By averaging the results from several maps, the resolution of the image was visibly improved. In addition, average daily canopy temperatures can be compared to crop specific optimum temperatures, to investigate physiologically significant patterns in the field. No adjustments to IRT mounting height or angle were made during this study. A larger portion of the field could be viewed by increasing the mounting height. However, this is likely to reduce the detection of small anomalies . Depending on the desired minimum unit management area, this may provide an alternative to increasing the number of IRT's to fully cover the field.

It is understood that the foregoing detailed description is given merely by way of illustration and that modifications and variations may be made therein without departing from the spirit and scope of the invention.

Claims

We claim:

1. An apparatus for selectively or simultaneously irrigating or mapping field or crop properties comprising: a) a field traversing irrigation system comprising

1) a sprinkler boom having a plurality of sprinkler assemblies mounted thereon, said sprinkler boom being effective for distributing water to each of said sprinkler assemblies;

2) a plurality of movable supports for supporting said sprinkler boom and which are capable of moving over said field; b) a plurality of sensors effective for measuring one or more field or crop properties mounted in an array along the length of said irrigation system; c) a position detector effective for determining the position of said sprinkler boom over said field; d) a microprocessor in communication with said sensors and said position detector which is effective for generating one or more maps showing the variance of the measured property across said field,

2. The apparatus of claim 1 wherein said irrigation system further comprises water delivery means effective for supplying water to said sprinkler boom.

3. The apparatus of claim 2 wherein said water delivery means comprises a water supply line in communication with said sprinkler boom.

4. The apparatus of claim 1 further comprising a sprinkler assembly control means in communication with said microprocessor effective for adjusting the volume of water sprayed from each of said sprinkler assemblies.

5. The apparatus of claim 4 wherein said sprinkler assembly control means is effective for independently adjusting the volume of water sprayed from each of said sprinkler assemblies .

6. The apparatus of claim 1 wherein said sensors are selected from the group consisting of non-contact surface temperature sensors, leaf N content sensors, leaf color sensors, soil organic matter sensors, and chemical vapor sensors.

7. The apparatus of claim 6 wherein said sensors are chemical vapor sensors selected from the group consisting of insect pheromone sensors and ethylene sensors for detecting ethylene .

8. The apparatus of claim 6 wherein said sensors comprise infra-red thermocouples.

9. The apparatus of claim 1 wherein said sensors are mounted in an array along the length of said sprinkler boom.

10. The apparatus of claim 1 wherein said sensors are mounted upon said supports .