Dr Andrew Landers

The blanket application of fertilisers and pesticides across a field is regarded by many as a waste of nutrients and chemicals. The soil varies across a field and so the resulting crop response also varies. Traditionally farmers have applied fertilizers across the field, irrespective of variations in soil type and nutrient status, resulting in over and under application in certain areas.

Legend has it that the North American Indians taught the early European settlers to place two fish underneath each corn plant to provide fertilizer for growth. In the corn (maize), cereals and soya bean areas of the mid-west of the USA, a number of companies and farmers are developing the use of Global Positioning Systems(GPS) to help them to apply seeds, fertilizer and pesticides accurately within the changing field conditions. GPS is also being used in conjunction with soil sampling and grain yield monitoring. The parallel development of computerised field maps and data recording has resulted in Geographic Information Systems (GIS).

The United States Department of Defence has implemented a network of 24 satellites, orbiting at nearly 11,000 miles, resulting in virtually all the USA having two-dimensional coverage for 24 hours per day. GPS satellites rotate the earth twice a day therefore their location relative to a given ground point is constantly changing, and so the satellites that are in view of a GPS receiver are constantly changing. If at least four GPS satellites are visible it is possible to obtain three dimensional coverage.

GPS receivers can determine their position by calculating the time taken for radio waves to travel from the satellite to the receiver. Radio waves travel at 186,000 miles per second and the GPS receiver has a built in clock that can accurately measure the time it takes for a satellite broadcast to arrive,the broadcast contains information as to the precise location of the receiver.

The Department of Defence reserves the right to distort the signal in times of military stress, known as Selective Availibilty (SA). The civilian receivers can therefore be inaccurate by up to 150 metres. To overcome this problem a receiver can be mounted on a precisely known, fixed position, eg a tower silo. This receiver can calculate the location of the satellites and then calculate the magnitude of introduced error. The differential corrections can be broadcast via a ground based radio link and sent to the tractor or combine harvester receiver which in turn can calculate its position to within 1-6 metres, this is known as differential GPS (dGPS).

1. The Satloc Satellite Differential (SSD) uses a network of ten reference stations precisely positioned at permanent locations throughout the USA. Each station calculates the differential for that area, then transmits a signal to a geostationary satellite which in turn, broadcasts back down to the user.The system is also referred to as Omnistar. The Omnistar system costs £4500 for a receiver and £4000 per year subscription fee.

2. The Coast Guard system is a navigation system covering the major rivers in the USA. A Tower system, it gives location within 150 - 200 miles of the tower.

3. The Rockwell Vision System comprises a display unit and a receiver. The display unit houses a computer and a memory extension card for yield information or for executing variable rate operations. A receiver picks up two distinct signals, signals directly from the satellites (GPS) and a corrected differential signal (dGPS) from a FM radio transmitter. Both signals are then correlated giving accuracies of 1-3 metres.

Differential Corrections Inc. (DCI) operate a system where the company has installed differential equipment on 67 FM radio station towers. The cost of the FM receiver is £250 and the differential signal costs between £50-400, depending upon the accuracy required, between 10 metres down to 1 metre.

4. SwathStar is a parallel swathing system for ground based applicators.Originally developed by Satloc for aerial application of pesticides and fertilizers, the system can be fitted to ground vehicles. A row of lights, mounted in the cab, tells the operator exactly when the vehicle is lined up for the next swath, thus eliminating the need for foam markers.The SwathStar is based upon the Satloc satellite differential system described earlier. The system allows operators to work at night, thus making better use of expensive vehicles. It should be noted that the use of 'tramlines' in fields is very rare in the USA.

A number of companies are offering computerised mapping systems which allows the farmer/grower to build up a series of layers for each field, this is commonly referred to as a Geographic Information System (GIS).

AgMAPP(TM) sell three mapping programmes:

1. AgMAPP(TM) GPS for creating field maps with GPS

2. AgMAPP(TM) 40 for record keeping, fertility management, planning and analysis

3. AgMAPP(TM) Farm Edition, a compilation of the above two systems.

AGRIS offer :

1. FieldLINK, a mobile mapping programme

2. AgLINK Field management programmes from Applications Mapping Inc.

Agris Corporation and Applications Mapping offer the following advice to farmers considering precision farming:

Step 1 Create a database of permanent soil characteristics

Step 2 Create a data layer of existing soil resources

Step 3 Record physical and regulatory constraints

Step 4 Generate detailed application and management plans

Step 5 Execute these plans using variable rate application controllers

Step 6 Monitor the results for initiating future diagnostic action

Electronic maps can be built up from several layers:

Soil type and topography

Soil test results showing nutrient status, organic matter, pH etc

Weed maps

Historic crop yields

Historic weather data

At one demonstration I attended in Illinois I saw the Concord 9300 soil sampler mounted on the back of a pick-up truck. The soil sampler comprises a sampling probe fitted onto the end of a jib. The jib works within an arc of the pickup truck, allowing samples to be taken and placed into a container, the arc ends at the cab door, allowing the samples to be collected by the driver without leaving his seat. The GPS receiver gave the exact location of the truck and up to six samples per minute can be taken.

At the same demonstration I saw a hand-held data collection computer, the Infielder Shortstop, based upon the Apple Newton, complete with differential GPS. The Apple Newton is a notepad computer and can be used for note-taking whilst soil sampling, crop walking, combining etc. The Infielder Shortstop has a mapping facility and can be connected to a desk-top computer. The Shortstop is being developed by the Monsanto Company.

The electronic maps will build a background picture, the farmer needs to use his/her experience and expertise to create an application strategy or prescription map remembering that the weather is the greatest factor which will affect yield.

The prescription map can be loaded into a computer in the cab of the tractor and grain drill, fertilizer spreader or pesticide applicator. The computer can be used to locate the tractor within the field using dGPS, then send signals to a controller which will adjust seed rate or fertilizer and pesticide rate whilst on the move.

On one the farms I visited in Illinois I saw an ACCU-PLANT programmable seeder control, manufactured by Rawson Control Systems, Inc., of Iowa. The system comprises a hydraulic motor drive for driving the planter mechanism, a radar gun ground speed sensor and a processor. The processor can give details of area sown, forward speed and distance travelled. When the system is connected to a computer with a prescription map, the seed population can be altered by turning a 32 position dial, each position giving changes in population by plus or minus 2%. For example, you may wish to alter seed population from 17,500 to 33,000 seeds/acre in 500 seed increments.

The farmer can create a prescription map, with changes in seed rate according to changes in soil type, nutrient value, trees etc.

The Tyler Flex-Air comprises a main 30 cu.m hopper and two supplementary bins for carrying dry fertilizer on a very large lorry. The cab has an on-board computer system comprising:

1. Flex controller which allows the operator to set spread rates, density and gate settings.

2. Ag Information manager which coordinates GPS/GIS positioning with the fertlizer rate maps and converts information for the flex-air system. As the Tyler Flex-Air travels across the field, the blend of up to three products and the application rate may change according to variations in soil/plant requirements. The Tyler Fluid-Air applies fertilizer between 5kgs-800kgs/ha and can be fitted with a Soil Monitoring and Application Regulator by Tyler (SMART), a probe connected to a soil engaging tine which electronically monitors the soil's organic matter and changes application rate on the move.

I visited with a number of fertilizer and pesticide distributors and one of the major points of discussion was the speed of loading the multi-product applicators, many of them preferred single product fertilizer spreaders due to the logistics of refilling a spreader with up to six products. The Soilection system has been established for some years, using the Soilection digitised map for varying soil types. The system, mounted on an Ag-Chem machine allows the blending of materials whilst on the move. I understand the machines are very expensive and there is a patent held by this company who threaten everyone who might infringe against their patent.

I visited Miles Farm Supplies, Owensboro, Kentucky, an extremely large agricultural suppliers and contracting company. To maintain and increase their customer base they need to be up to date with their application technology and are using variable rate application on their fertilizer applicators connected to GPS. Miles Farm Services offer OptiCrop, a consultancy service which employs two Englishmen for agronomy advice. Miles Farm Supplies are also using the SwathStar parallel tracking system mentioned earlier.

At one fertilizer distributor I saw a prototype spreader using a Mid-Tech TASC 6200 controller, connected to an Applications Mapping programme. The vehicle was fitted with GPS and the TASC 6200 controller which alters fertilizer rates whilst on the move by adjusting the speed of a hydraulic motor which is driving the unloading conveyor belt. A small printer gave the output of the product for each field.

The Mid-Tech TASC 6200 can also be used for varying the rates whilst applying pesticides across a field, using GPS and a mapping programme. The farmer/agronomist can create a weed map, and, within certain grid areas, prescribe varying amounts of pesticides. The use of a direct injection sprayer allows various pesticides to be blended whilst on the move. I came across two well proven systems, the Mid-Tech injection system, which uses peristaltic or tube pumps and the Raven injector which uses a positive displacement pump.

Raven Industries, Micro-Trak Systems and Mid-Tech are very active in promoting their controllers for any application control situation within precision farming.

The final part of the precision farming jig-saw is grain yield monitoring on combine harvesters. Two companies were developing systems at the demonstrations I attended.

Micro-Trak systems use a sensor installed in the clean grain elevator which records the flow of grain by measuring the force applied to a sealed load cell, nearby a grain moisture meter is fitted to detect changes in moisture. Data-Trak and Grain-Trak are part of a system called Trak-Net, a GPS based positioning and data recording system.

Ag Leader Technology also produce a grain yield monitoring device based upon a deflector plate and moisture meter, situated in the grain tank elevator.

Whilst in the mid-west I met a number of farmers who are practising precision farming, the most impressive farmer is undoubtedly Kent Brewer of Indiana. Kent farms approximately 600 hectares of crops. The following information details his precision farming system:

Computer software:

The CropSight field mapping programme creates field maps on a 486 PC which can be downloaded via a datacard to a 386 laptop in the truck cab. MapLink software sends signals to the sprayer controller to adjust application rates.

GPS:

Differential GPS is provided by Unilink, a GPS and differential signal (DCI) provided from a FM radio tower 28 miles away. Cost is £400 per annum subscription for the signal and box and £1200 initial cost.

Soil sampling:

100 metre by 100 metre (1 hectare) grids are used which fits in well with the spreader/sprayer boom widths. An ATV, fitted with a laptop computer uses Maplink 2. A bullseye cursor is used which pinpoints the cursor centre and the 12 samples are taken around the spot with a hand auger in a 10 metre radius. Soil samples are taken by the 10th June so that the crop can be checked for thistle patches, it also allows the summer to set up a prescription. Samples are sent to a lab for analysis at £7.80/ha. and gives details of N,P,K, Boron, pH, O/M and gives recommendations. The service is cheaper without the recommendations.

There are thirteen different soil types on the farm, one of the fields I was shown had eight different soil types. Variation in pH in another field varied between 5.8 and 6.9. Lime is spread to create pH7.0.

Fertilizer use:

An 18 metre broadcaster with a variable speed unloading belt is used. Variations in rates are from 160-230 kgs/ha.

Seed planting:

Currently devising his own trials, especially where soil types border each other. GPS and a rate controller on the drill allow simple trials to be carried out easily.

Pesticide application:

Kent built his own sprayer, based on a GMC one-ton truck. The unit comprises a 18 metre Ag-Chem boom and 1800 litre tank which cost around £14,000, £9000 of which was spent on a set of three Mid-Tech injection pumps, TASC6500 controller and a navigation system which is easily transferable to other operations such as the seed planter, Ammonia applicator, fertilizer and soil sampler.

Pesticide use:

Bicep, a pre-plant application for Corn (maize), is applied at varying rates according to organic matter content of the soil, rates varied from 4.25 to 6.75 litres per ha. Previously Kent had applied 6.75 litres as a blanket rate over the whole corn crop, this year he applied an average of 5.9 litres/ha, resulting in a saving of £1800.

Variable rates of 2,4-D, Sencor, Pounce and Pursuit should lead to more savings.

Combine harvesting:

A Case IH combine is fitted with an AgLeader grain yield and moisture meter. The system needs very careful setting up/calibration and was only 23 bushels out on 1600 tons sold.

Kent Brewer has developed the whole precision farming system on his own, he is typical of the modern young farmer who realises that computers can aid farm management and that precision farming is yet another aid to management. Kent Brewer went into precision farming "to lower costs and improve income, fertilizer is the greatest saving. The first goal is to balance the pH across the whole farm.

1. The technology for precision farming already exists and just needs fine tuning for agricultural applications.

2. The principles of precision farming are readily transferable to the UK, at times I believe engineers often re-invent wheels because of their 'not invented here' attitude.

3. I question if agronomy has kept pace with the technological developments and I wonder who will advise the farmers about their agronomic decisions.

4. The use of precision agriculture will help reduce wasted inputs on arable farms, allowing greater benefit to be made of expensive inputs.

5. The farmer/grower must identify why he is considering precision farming. Yields can be maintained with reduced inputs or, alternatively, yields can be maintained but increased inputs can increase quality.