Carl & Janice Mattson

RO. BOX 382

CHESTER, MT 59522

PHONE: 40~292-3B23

FAX: 40~292-3631

Ever since we became an active part of our farm's production process twenty years ago, Janice and I have been trying to identify and locate agricultural areas of concern, on our acreage, in northern Montana. ~ started in the late seventies by drawing, to the best of our abilities, the location of wild oat infestations on our ASCS maps during harvest This, in itself, was not a particularly difficult task but it did mean that one peon that knew the fields and was operating a combine from the beginning of harvest to the end, needed to do the mapping. That person, somewhat reluctant at the time, was Janice. In the years that followed she provided our operation with maps that were accurate enough to use when applying granular wild cat herbicides and subsequently, we were able to maximize the effectiveness of our wild oat control effort while minimizing the time and dollars being spent in the process. After this initial start in mapping oats, we added to the system by mapping various other types of weed problems spotted during harvest.

This system worked very well in the strip style of farming that we were using at the time. Our fields were all 330 feet wide, ran north and south, one mile in length, and alternated cop fallow across the landscape, thereby creating a giant piece of graph paper which for the most part enabled us to know quite closely where we were east and west, north and south. Distances, however, were more of an approximation. Nonetheless this worked for us until we started to fallow. Shortly after changing into the chem fallow scheme of things it became obvious to us that there was no longer a need to keep our fields in narrow strips in order to control soil erosion; so in the late 80 s we started to turn our property, which had been in strips since it was broken up, into blocks. The block system, chem fallow, and the no-till system that we are practicing now made it impossible for us to continue using our strip edges and ASCS maps to locate the wild oat problem areas. ~ struggled with the problem and made due until we came across the concept of GPS in 1992.We immediately knew that GPS had a great many possibilities in agriculture however, there was a tremendous amount for us to learn before it could possibly become a useful tool on our farm. The more we looked into GPS the more we liked the whole idea but the educational opportunities required more computer background than I had, so Janioe set out to become our resident expert.

As our understanding of GPS grew, so too did our imagination as to what else we could use it for. At the time we were involved in trying to figure out how to plant into the large amount of stubble that I was creating in the no-till process. After extensive research did I purchased a Concord air till drill. Nat only did the four rank drill give me superior trash clearance but by its design it was nearly factory ready for a controller vary fertilizer.

SITE SPECIFIC FARMING

Somewhere within this timeline the term "SITE SPECIFIC FARMING came to my attention and much to my amazement after attending several conferences on the topic, we realized that we were, to an effect, already engaged in an abbreviated form of this very idea. However, with GPS the reality of being able to accurately relocate an exact point on earth opened the door to an endless list Of possibilities never been imaginable on our farm.

During the course Of the next few pages we will try to convey some of our experiences in hopes that this may help others

1. Sight specific farming is a concept, you cannot buy it off the shelf.

2. The concept must be thoroughly studied in order that each individual farm operator, can determine whether or not he can benefit by being able to identify very small parcels of a particular field, and measure that parcelÌs inputs and outputs.

3. If the operator determines that there is a benefit to be had then he must decide what he desires to measure.

4. Once he has determined what it is that he wants to measure then he must decide which tools are available to accomplish this task

5. With the appropriate tools in hand collect the information.

6. Make management decisions based upon the collected information.

7. Decide what you want to vary.

8. Decide how to vary that product

9. Do it

10. Measure and test the results at harvest.

We had already determined that we wanted to measure yield, and with the purchase of an Ag Leader yield monitor in 1994 we kept track of the yield field by field. In the past we had always ays worked and felt comfortable with a field or farm average but now for the first time we were visually watching those individual yield notations that have for years, made up our field and farm averages. We were surprised in that the highs were higher than we had anticipated and that the lows were lower. Another very interesting observation was that the highs and lows were not necessarily located where we had always assumed they were. All in all the yield monitor proved to be a very valuable tool. It was able to show, us that we had a great deal of variance and we looked upon this variance as an economic opportunity.

With this degree of variance witnessed, we next set upon the task of tagging a particular yield to a particular parcel of land. This meant that we needed to choose a GPS system and get it up and running prior to the next harvest. originally our intentions were to map yield the same year that we purchased the yield monitors however we found it impossible to find a GPS system that was available and suitable to our needs at that time, the summer of 1994.

WILL THE WHOLE PROCESS PAY

We have had five years on our operation to move towards Site Specific Farming and during that time there was very little hard and fast information available concerning the economic viability of what we were trying to do. Because of that we had to rationalize the concept in our own way.

It is within the realm of soil fertility that we found what we believed to be the most promising economic possibility for us to pursue in site specific farming. In the beginning, fertilizer recommendations were basically the same for the entire dry land farming region of Montana which extends from the eastern slope of the Rocky Mountains to MontanaÌs eastern most boundary. With time these recommendations were refined to regions within the state, based mostly upon rainfall probabilities, later on farm recommendations evolved, and with more widespread soil testing capabilities, individual field recommendations became practical. Each and every time these recommendations were refined in order to represent a smaller area than before, the producer was rewarded for being more specific.

It is this reward that we have been in pursuit of and it is our belief that if we are able to accurately prescribe fertility requirements for individual zones within a field we will once again became the benefactor for simply being more specific. The whole concept at this point becomes very involved, because one must now, take into consideration not only available moisture, plant variety, and soil fertility but he must apply that knowledge to the variances in such things as soil type, slope, and yield. Hopefully some day soon "on the go" protein sampling will be available to help in the equation.

In the fall of 1994 researchers at MSU Northern Research Center in Havre Montana completed the first year of a multi year study that dealt with varying the rates of nitrogen on wheat, in a fashion that attempted to match optimum fertility with soil variability, within a particular field. Their results show promise in that they were able to define a financial gain on the acres studied. With the permission of the research team we have attached their paper as appendix" A". In 1995 they expanded the research to include a study of the effects of varying phosphorus in the same manner. The results of 1995 are not in print at this time however, the preliminary results once again appear to be promising.

SO WHERE ARE THE MATTSONS AT THIS POINT IN TIME

Together we are operating 5500 acres, 4500 of which was planted to wheat in 1995 and 1000 acres in chem fallow. In the spring 1994 we had the ability to vary nitrogen manually manually from the tractor cab during planting and did so with a Rawson variable rate controller. We are planting with a 50 foot four rank Concord air till drill and two tanks; a 2400 tow, between in which we put seed and phosphate and a 3000 tow behind in which we put urea. We are placing the seed and phosphate together in a 5 inch spread while deep banding the urea below. During the summer of 1995 we purchased an Ashtech differential GPS unit and fully intend to vary urea and apply granular wild oat herbicide via the computer during the planting process in the spring of 1996.

In 1995 with the arrival of the Ashtech GPS unit we finally were able to map the yields and wild oats during harvest October of 1995 was the month during which Janioe was able to use our first yield maps with information from our own property. ~ were harvesting with three GPS equipped combines.

During the summer of 1995 we purchased a double boom 130 foot Flexicoil sprayer. We equipped this unit with a Mid-Tech spray controller and retrofitted the tank cart to carry the equipment and chemicals necessary for an injection system. The plan here is not only to use the GPS and the computer for very accurate guidance but also to be able to vary chemicals where possible during spraying, and to be able to change automatically to a separate chemical mix by switching to the second boom when the sprayer enters one of the wild oat zones that were identified during the previous harvest. The effectiveness of this operation will be relatively easy to monitor by being able to relocate the exact areas where the oats were identified and the herbicide applied.

For many years now we have been doing our own soil probing and sending the samples a way for analysis. ~ have tried very hard to mark on our ASCS maps approximately where we have taken the samples. It is our feeling that it is necessary when comparing test results from year to year, that the samples are drawn from the same location. In the past we have been dose but in 1996 we intend to locate the sample points with the GPS and in the following years return to these exact locations, sample, and review the results.

A SUMMARY OF POSSIBLE FARM USES FOR GPS

1. Mapping

A Yield

B. Fertility

C. Soil Type

D. Soil Moisture

E. Field Slope

F. Weed Infestations

G. Field Boundaries

H. Measuring Acreages

I. Underground Power, Water Lines, Tiles

J. Farmstead Physical Characteristics

2. Varying Inputs

A Fertilizer

B. Seed Density

C. Changing Seed Varieties

D. Chemicals

3. Guidance

A Seeding

B. Spraying

C. Relocating Attributes

WHAT IS GPS AND HOW DOES IT WORK

The Global Positioning System, or better known as GPS, is not a new technology. As citizens, we heard and read about the success of its use during Desert Storm which provided the accuracies necessary for the bombing of specific predetermined locations mapped via GPS. The GPS system was designed and used in the 1970's as a military navigation system providing positioning all over the world. Throughout the 80's and early 90's the GPS technology was used mainly in the mining, oil, and surveying industries. Only recently has the interest and demand for this technology come from the agricultural community, which has been promoted by the introduction of agricultural equipment that can now integrate 'with the GPS

The GPS constellation consists of 24 satellites in five orbital planes, circling the earth at an altitude of 20,000 km with twelve hour orbits providing twenty-four-hour coverage of five to ten visible satellites 'worldwide. During our harvest season in 1995, 'we 'were viewing usually 8 satellites and often 10 satellites at any given time. The satellite system is tracked continuously from five stations on earth. Tracking data provides an ephemeris, or an equation relating the position of each satellite to time. This information is then uploaded from a control center in Colorado Springs to each satellite at eight hour intervals and downloaded to each GPS user "in the field" as range measuremeets are made. A position in space can be determined by measuring distances from three points of known position. This gives a horizontal location. "'hen the demand for the technology moved from marine navigation to land navigation, observations from a fourth satellite became necessary to determine elevation.

Signals from each GPS satellite contains precise timing and position information. Each GPS satellite transmits these signals on two frequencies, LI and 1-2. A standard code, referred to as C/A code, is transmitted in L1 and a precise code, referred to as P code, is transmitted on bath L1 and 12. The more precise information obtained from the "P Code" is currently available only to the military and selected civilians. A GPS receiver may use this coded signal, the carrier phase of the signal, or a combination of both to determine a position. Use of a combination of these observables in a receiver determines the amount of accuracy in a particular receiver, which also determines the cost of that receiver-, the more accurate the receiver, the more expensive it is.

There exists two methods for denying civilian users full access to the GPS One is Selective Availability, referred to as "SA", and the other is Anti Spoofing, known as "AS,'. Selective Availability is accomplished by intentionally introducing error into the satellite docks (dithering) and also by limiting the users knowledge of the satellite position by truncating the broadcast satellite navigation message, the ephermeris. Both of these effects are largely overcome by using differential -positioning techniques mentioned later.

Anti Spoofing is the practice of encrypting precise code (P code) into a Y code, riot generally available to civilian users. Its purpose is to discourage use of the system by an unfriendly group or individual sending out a false signal which would mimic the GPS code and in turn confuse system users. Just recently some federal agencies in the Department of Ag have been allowed to use the encrypted P code but it is not felt that this access will be widespread in the future.

The accuracy of a position determined by GPS varies from a few millimeters to several hundred meters, and is influenced by the following factors.

I. Type of receiver used

2. Type of measurement used by the receiver - code,, carrier phase, L1, 1-2 frequencies

3. Number of salellites observed by the receiver

4. Length of observation

5. The geometric distribution of satellites

6. Position of the antenna of the receiver

7. The type or receiver antenna being used

8. The processing alogorithm used by the receiver to determine position

9. The atmosphere, troposphere, and ionosphere; all of which have an effect on the signal between the satellite and the user

The geometric strength of the satellite constellation changes with time, and is best when a large number of satellites are visible and well distributed throughout the sky. A receiver may be watching five or more satellites but the strength of the constellation may be poor due to their locations in the sky. A measure of the strength is indicated by what is called the Dilution of Precision (DOP) values which are generated by the software or firmware associated 'with each GPS receiver.

Historically, receivers produced by a particular manufacturer would output data in that manufacturer's prorietary format. The format Of the signal was most Often specific to the manufacturer's equipment and receivers that that particular manufacturer produced. In agricultural applications, where GPS receivers are supplying data to computers, equipment, controllers, and a variety collection devices made by many different manufacturers1 a data format coming from the GPS receiver that is a standard format is desirable. The National Marine Electronics Association (NMEA) has developed such a standard known as NMEA 0183, which is now being followed by many GPS receiver manufacturers. When purchasing products you plan to integrate into your farming system, it is important to know with what format the manufacturer intends to interface.

I have heard comments from those unfamiliar with the GPS system and how it works, believing that if the government would just turn off SA, we wouldn't need all these expensive receivers to acquire the accuracy we are demanding. A receiver using the standard position service CIA code on L1 frequency, can only be accurate to a few tens Of meters 'with SA "Off" and approximately one hundred meters when SA is turned "on". If Selective Availability was indeed turned Off, the accuracy then obtained Of 15 feet 'would riot be adequate for the applications 'we intend to use on our farm.

The most widely used technique used for improving the accuracy Of a GPS position is known as differential GPS (DGPS). This requires two GPS receivers. One receiver is placed on a known position (the longitude and latitude is known) in your yard, for example. The second receiver (rover) is located on a unit "in the field", whether it be the tractor when varying fertilizer or chemical rates, the combine to record positions when gathering yield information, or the four wheeler you take out to the field to map boundaries, 'weed or disease infestations, etc. The receiver over the known point, compares the position it receives directly from the GPS satellites to the known point the receiver knows it is over. This "correction" in position is then applied to the rover in the field. As the distance between the base and roving receiver increases, the accuracy of DGPS diminishes. In the system 'we are using with the home base tower supplying the corrected signal, the distance between the base and the roving using should be limited to 60 miles.

The terminology for the process of recording DGPS positions "on the go" as you are gathering data, is "real time". For this to work, a data link must exist between the two receivers. In our case, we are using a radio frequency comrnunication between the two receivers. Systems are available through which you do not record positions "on the go". With these systerns, the positions of both receivers (the one over a known point and the receiver on the rover) are gathered from the satellites and are received on a computer. The more accurate positions of the rover are determined after the collecting session is over. This is known as "post processing". If you want to be in the field varying rates, you must be using "real time" positioning.

In a "real time" positioning process in order to make the data link between a home base station and the roving unit standard, the Radio Technical Commission for Maritime Services (RTCM) was asked to develop standards for transmitting differential corrections. These standards, known as RTCM SC-104, are now used by many data link operators and are expected by many GPS receivers.

How can you obtain a real time differential correction where you are located? In some areas of the country you may have several choices, while in others you may have only one choice. One option is to install a local or home differential base station. This consists of a GPS receiver and usually a radio modem to transmit the differential correction to a remote mobile receiver, which also contains a GPS receiver and a radio receiver. Ideally, the local base station is placed on a known position and differential corrections are computed from that known position. When a known point is not available, the base station can be used to determine a starting position. Howeve, this position may be in error by as much as 100 meters, because it is typically determined by a single point CIA code solution. This scenario is referred to as the "fence post" base station. While an error of 100 meters in the actual location of the base station 'will have a slight effect on the accuracy of the differential corrections computed from the point at a given time, a more serious problem exists when one attempts to overlay different data sets over time on top of each other. The data sets are all floating around in space, relative to the receiver on the "fence post'. This is a concern for the producer who wishes to collect years of data sets and wants to overlay different layers of information. The boundaries of these data sets 'will not lie on top of each other when the "fence postÓ is not fixed over a known location on earth.

In regard to the radios necessary to provide the data link beteen the horne base station and the rover1 there exists a variety of radios that can transmit on different watts Of power The choice would are dependent upon the geography Of the area farmed and the distances to be covered. These radios transmit through and around solid obstacles at dose range, but near the limits of the radios, they become limited to line of site.

A second option in acquiring differential corrected signals might be the FM Sub Carrier. There have been several commercial firms that have established networks of GPS base stations located at FM radio stations transmitting the corrected signal as a home base station would, using a standard format called RTCM SC-104. An individual purchases an FM radio receiver capable of receiving the corrections and then pays an annual subscription for that service. The subscription rate typically costs several hundred dollars a year and may be available at several different accuracy levels. The effective distance at which these services can be used depends on the location of the transmitting tower and the power of the signal. The accuracy of the position computed from the differential correction diminishes as the distance to the tower increases, but usually the FM signal is lost before accuracy becomes a serious consideration. Although the amount of accuracy may be changing, at this time, most FM services do not attempt to provide a correction accuracy better than one meter. The ultimate accuracy 'will depend on both the differential connection and the user's GPS receiver.

A third option is the Coast Guard Corps of Eng. Beacon. The US Coast Guard is implementing a differential correction service for harbor and harbor approaches along the coasts of the US, through the Great Lakes, and on the navigable Inland Rivers. The service is expected to be fully operational by the end of 1996. This system will provide coverage to a substantial agricultural area. The user must have a radio beacon receiver and a GPS receiver capable of using the RTCM SC-104 correction messages. Several companies in the US and Canada are currently marketing the radio beacon receivers, and many GPS receivers are compatible.

As I mentioned before, as the distance between the reference station (whether it be a home base or a FM station) and the roving receiver increases, the accuracy of the corrected position decreases. An alternative approach is a Wide Area Differential GPS (WADPGS) network. This systems consists of a network of a number of reference stations situated over known locations around the United States, a central control station where the connections will be computed with constant, real time communication (telephone) from all the reference stations. A real time data link must be established between the central control station and each user. This can be established by using a geo-stationary communications satellite (orbits around the earth's equator). The user must have a radio capable of receiving differential correction information from the communications satellite, and a GPS receiver which will produce an initial position estimate, plus software to compute the corrections and apply them to an observed position. One commercial service is available in the US providing this signal. This is the service that John Deere is providing with their "GreenStar' system. The subscription rate for this service is related to the accuracy provided.

How does one choose which correction device to use?

1. Research what services are available in your geographical area

2. Decide what accuracy your application will demand

3. Determine the distances you need to encompass

4. Compare the total costs of the different systems available (i.e. how long will it take for a service requiring a subscription rate to equal the cost of a home base?)

5. Decide if you want to maintain full control of the system

6. Decide if you would consider "sharing" a hone base system with some nearby neighbors.

As Carl has already mentioned, when attempting implement the full cycle of site specific farming and GPS1 look at the entire picture of all that is involved. I believe it is important to find a company that can help you integrate all the different aspects of the site-specific cyde:

1. Find a company that can prov'ide the GPS signal to the accuracy your applications will demand.

2. Before purchasing equipment ensure that it is GPS ÏreadyÓ, meaning it is capable of communication with a computer (usually through a serial port).

3. You will need someone to provide the software that can communicate with the machinery you chose to purchase.

4. Once you have gathered all the data you intended to collect, you will then need a GIS (Geographic Information System) software -package that can tie all this Information together in a format you can analyze. The GIS software maintains a database of the attributes recorded, and keeps those attributes "tied" to a position on earth.

REFERENCES

David A Tyler, Ashtech/Springhill Engineering Division, Belgrade, MT

Douglas W Roberts, Engineer, Ashtech/Springhill Engineering Division, Belgrade, MT Gerald A Nielsen, Professor, Dept. of Plant, Soil and Environmental Sciences, Montana State University, Bozeman, MT

Dan Long, Site-Spedfic Managment Scientist Northern Agricultural Research Center NSE 36 Box 43, Havre, MT 59501

Gregg Carlson, Agroncnist, Northern Agricultural Research Center, SE 36 Box 43, Havre, MT 59501

To obtain more information about the products we have mentioned in the above paper feel free to contact us personally or the companies directly:

Concord, Inc.

28007th Avenue North

Fargo, ND 58102

Ag Leader Yield Monitor

Allen Myers

1203A Airport Road

P.O. Box 2348

Ames, IA 50010

Mid-Tech

Midwest Technologies, Inc.

2733 East Ash Street

Springfield, IL 62703

AocL~Plant

Rawson Control Systems, Inc.

1162nd St. SE.

Oelwein, Iowa 50662

Montana AgResearch Spring 1995