GPS APPLICATIONS IN AGRICULTURE, CONT'D

1. Equipment/Tractor Guidance Systems

Farmers cannot put their tractors on auto-pilot. If they plough their fields with a recording GPS system the tractor can then be programmed to follow the same route - for cultivating, fertilizing, pest control and harvesting. The programming of tractor routes has the potential to save a lot of money. Several manufacturers are currently producing guidance systems using high precision DGPS that can accurately position a moving vehicle within a foot or less. These guidance systems may replace conventional equipment markers for spraying or seeding and may be a valuable field scouting tool. 

Lightbar-guided and automated steering systems help maintain precise swath-to-swath widths. Guidance systems identify an imaginary A-B starting line, curve or circle for parallel swathing using GPS positions and a control module. The module takes into account the swath width of the implement and then uses GPS to guide machines along parallel, curved, or circular evenly spaced swaths. Guidance systems include a display module that uses audible tones or lights as directional indicators for the operator. The guidance system allows the operator to monitor the lightbar to maintain the desired distance from the previous swath.

Guidance systems require two principle components: a light bar or screen, which is essentially an electronic display showing a machine's deviation from the intended position, and a GPS receiver for locating the position. This receiver must be designed for this purpose and it must operate at a higher frequency (position calculations are usually 5 to 10 times per second) than a GPS receiver designed to record positions for a yield monitor. GPS receivers designed for guidance can be used in conjunction with a yield monitor or for other positioning equipment.

Automated steering systems integrate GPS guidance capabilities into the vehicle steering system. Automated steering frees the operator from steering the equipment except at corners and at the ends of fields.

An Example of Swath guided GPS system

• ·         Anchor points established to create base line on map screen.
• ·         Parallel lines generated at desired swath spacing.
• ·         Can be used for straight or contour swaths
• ·         Light bar or similar device used to provide guidance along line.
• Automatic steering possible.

2. Yield Monitoring Systems

Estimates of yield variations across a property can be made using GPS. To do this the property is divided into zones and the yield of each zone is estimated and plotted on a map. The map can then be used to better understand the property and for decision-making in regard to the next planting.

Yield monitoring systems typically utilize a mass flow sensor for continuous measuring of the harvested weight of the crop. The sensor is normally located at the top of the clean grain elevator. As the grain is conveyed into the grain tank, it strikes the sensor and the amount of force applied to the sensor represents the recorded yield. While this is happening, the grain is being tested for moisture to adjust the yield value accordingly. At the same time, a sensor is detecting header position to determine whether or not yield data should be recorded. Header width is normally entered manually into the monitor and a GPS, radar or a wheel rotation sensor is used to determine travel speed. The data is displayed on a monitor located in the combine cab and stored on a computer card for transfer to an office computer for analysis. Yield monitors require regular calibration to account for varying conditions, crops and test weights.

Instantaneous yield monitors are currently available from several manufacturers for all recent models of combines. They provide a crop yield by time or distance (e.g. every second or every few metres). They also track other data such as distance and bushels per load, number of loads and fields.  

3. Field Mapping with GPS (and GIS)

GPS technology is used to locate and map regions of fields such as high weed, disease and pest infestations. Rocks, potholes, power lines, tree rows, broken drain tile, poorly drained regions and other landmarks can also be recorded for future reference. GPS is used to locate and map soil-sampling locations, allowing growers to develop contour maps showing fertility variations throughout fields. The various datasets are added as map layers in geographic information system (GIS) computer programs. GIS programs are used to analyze and correlate information between GIS layers. Examples of the mapping would include:

• Soil Sampling

 Collecting soil samples across a large property can be organized using GPS and mapping software. The sample locations can be way pointed in the field and those waypoints marked on the mapping software. Then, when the laboratory results are returned the data can be plotted on the maps and decisions for soil treatment can be made for various parts of the property. The locational information can save money and time by allowing variable rate applications and treating only those areas with a documented need.

Soil Sampling methods include:

     1. Grid Sampling- intensive sampling of entire field

-Data collected for each cell or point.

-Multiple samples combined into each cell or point sample.

     2. Directed sampling:  intensive sampling of particular target areas.

-Sampling zones established based on knowledge of field

-GPS used to locate sample points.

-Areas of interest intensely sampled, others lightly sampled.

An example of a semi-automated Soil Sampler

• Weed mapping and Pest mapping

A farmer can map weeds while combining, seeding, spraying or field scouting by using a keypad or buttons hooked up to a GPS receiver and data logger. These occurrences can then be mapped out on a computer and compared to yield maps, fertilizer maps and spray maps. The same procedure is used while mapping pests in a field.

• Crop duster targeting

Insects don't attack a field with a uniform distribution. Instead outbreaks of insect activity are concentrated in certain areas. Workers strolling the crops can use a GPS to record the locations of insect problems. The data can then be used by crop-duster pilots to selectively target the problem areas instead of treating an entire field. This method results in a savings of time, fuel, insecticide and crop exposure to chemicals.

• Salinity mapping

GPS can be coupled to a salinity meter sled which is towed behind an ATV (or pickup) across fields affected by salinity. Salinity mapping is valuable in interpreting yield maps and weed maps as well as tracking the change in salinity over time.

• Topography and boundaries

Using high precision DGPS a very accurate topographic map can be made of any field. This is useful when interpreting yield maps and weed maps as well as planning for grassed waterways and field divisions. Field boundaries, roads, yards, tree stands and wetlands can all be accurately mapped to aid in farm planning. 

4. Precision Crop Input Applications/Variable rate applications

Crop advisors use rugged data collection devices with GPS for accurate positioning to map pest, insect, and weed infestations in the field. Pest problem areas in crops can be pinpointed and mapped for future management decisions and input recommendations. The same field data can also be used by aircraft sprayers, enabling accurate swathing of fields without use of human “flaggers” to guide them. Crop dusters equipped with GPS are able to fly accurate swaths over the field, applying chemicals only where needed, minimizing chemical drift, reducing the amount of chemicals needed, thereby benefiting the environment.

GPS technology is used to vary crop inputs throughout a field based on GIS maps or real-time sensing of crop conditions. Variable rate technology requires a GPS receiver, a computer controller, and a regulated drive mechanism mounted on the applicator. Crop input equipment such as planters or chemical applicators can be equipped to vary one or several products simultaneously.

Variable rate technology is used to vary fertilizer, seed, herbicide, fungicide and insecticide rates and for adjusting irrigation applications. Variable rate controllers are available for granular, liquid and gaseous fertilizer materials. Variable rates can either be manually controlled by the driver or automatically controlled by an on board computer with an electronic prescription map. E.g, by knowing weed locations from weed mapping spot control can be implemented. Controllers are available to electronically turn booms on and off, and alter the amount (and blend) of herbicide applied.
An example of a Variable Rate prescription map

5. Yield mapping
GPS receivers coupled with yield monitors provide spatial coordinates for the yield monitor data. This can be made into yield maps of each field. 

6. Tracking Livestock: 
The location of valuable animals on a large farm can be monitored by GPS transmitters attached to the animals collar. When the animals are sent to market GPS transmitters can also be used to track their location.

7. Records and analyses
Precision farming may produce an explosion in the amount of records available for farm management. Electronic sensors can collect a lot of data in a short period of time. Lots of disk space is needed to store all the data as well as the map graphics resulting from the data. Electronic controllers can also be designed to provide signals that are recorded electronically. It may be useful to record the fertilizer rates actually put down by the application equipment, not just what should have been put down according to a prescription map. A lot of new data is generated every year (yields, weeds, etc). Farmers will want to keep track of the yearly data to study trends in fertility, yields, salinity and numerous other parameters. This means a large database is needed with the capability to archive, and retrieve, data for future analyses.