Precision Agriculture

Crops in the Southeastern United States are generally produced in fields known to have a high degree of variability in soil type, topography, soil moisture and other major factors that affect crop production. Precision agriculture is a promising management tool that can enable the development of an agricultural system to effectively manage fields to account for this variability. The cornerstones of precision agriculture technology include the Global Positioning System (GPS), Geographic Information Systems (GIS), and variable rate equipment and controllers.

The potential impact to producers is reduced pesticide and nutrient use and thereby reduced input costs. Spatial-based information will enable growers to apply inputs (pesticides, nutrients, irrigation, etc.) only to locations and in the amounts needed in the field. Producers also benefit by the increasing availability of better and timely information about their crops for decision-making.  They will be able to denote problem areas in a field before problems become visible and before it is too late to take corrective action.  The impact to consumers is a cleaner environment and continued supply of good quality food at a reasonable cost.  The ultimate outcome of the adoption of precision agriculture will be to enhance the competitive position of U.S. Agriculture and improve stewardship of the environment.

GPS based tractor guidance

Auto guidance, a technology that pilots farm machinery via GPS satellites, could help farmers boost productivity and expand their farm operations.  Benefits of GPS-based guidance include: reduced skips and overlaps, ability to use in conditions of poor visibility, keeps implements in the same traffic patterns year-to-year (controlled traffic), extends hours of operation, low-skilled tractor drivers, increased yield, energy and time savings, increased application accuracy, and enhanced operation safety.

There are two major categories at which GPS-based guidance is being offered: Navigation aids and Auto-guidance.

Relatively inexpensive navigation aids known as parallel tracking devices or, more commonly, Lightbars, are being used by operators to visualize their position with respect to previous passes and to recognize the need to make steering adjustments. The Lightbars are replacement for foam marker and are suitable for fertilizer and pesticide applications.

Positional accuracy depends on the quality of the DGPS receiver supplying data to it and the driver’s ability to “follow the lights” Most DGPS receivers used with Lightbars are sub-meter accuracy. Price ranges from $1,700 to $4,700 depending on GPS Receiver and options.

More advanced auto-guidance options possess similar capabilities with an additional option to automatically guide the vehicle. The accuracy of the auto-guidance can be described either from a long-term static test (year-to-year accuracy) or short-term dynamic test (pass-to-pass accuracy). Year-to-year accuracy is important when different field operations are expected to be performed using exactly the same passes (such as controlled traffic, harvesting, etc.). On the other hand, many field operations (such as fertilizer spreading, disking, etc.) can tolerate long-term inconsistency of measurements obtained. Therefore, errors expected within 15-minute time intervals are more commonly reported when characterizing less accurate systems. Based on the quality of differential correction and internal data processing, the guiding systems have been separated into three categories:

Sub-meter accuracy usually means approximately 2-4 foot year-to-year and less than 1 foot pass-to-pass errors. The Differential GPS source could be from Coast Guard beacon, WAAS, OmniSTAR, and John Deere StarFire1. The OmniSTAR requires an annual subscription fee. These systems are relatively inexpensive (about $6000 to $15,000) and can be used An example of a sub-meter system while performing tillage, some types of fertilizer and chemical applications, seeding and harvesting. However, operations requiring highly accurate guidance are not feasible with sub-meter level equipment. These devices can be easily transferred between vehicles, so the same steering system can be used on different vehicles.

Decimeter accuracy approximately 4-8 inches year-to-year and 3-5 inches pass-to-pass errors are feasible with decimeter accuracy systems. This can be achieved using either a local base station or dual frequency receivers with private satellite differential correction services, such as OmniSTAR High Performance (HP) or John Deere StarFire 2 (SF2). With the increased performance, operators can use auto-guidance during most of the conventional field practices excluded above. Price ranges from $15,000 to $25,000 + OmniSTAR HP subscription ($1500 annually).

Centimeter accuracy can be obtained when a local base station with the Real Time Kinematic (RTK) differential correction is used. Both long-term and short-term errors for these systems have been reported around one inch. Vehicles equipped with this high-level An example of a RTK system equipment can be used to conduct strip tilling, drip tape placement, land leveling and other operations requiring superior performance, as well as virtually any other task. In addition to the ability to accurately determine geographic location, auto-guidance systems usually measure vehicle orientation in space, and compensate for unusual attitude, including roll, pitch and yaw. Price ranges from $40,000 to $50,000. Return to top.

Variable-rate application of crop nutrients

The concept of site specific application of fertilizer is not new. Historically, fields were smaller than they are today and small areas within fields were frequently fertilized differently than the major portion in order to address special requirements for either nutrients used or rate of application. Today, computers and guidance systems have largely replaced techniques like counting rows or looking for atypical areas within a field. In addition, new technologies such as soil EC meter and the yield monitors have increased the awareness of variability within fields.

In general, there are two sampling strategies (grid, zone) that can be used to direct site-specific fertilizer management and lime application. Grid sampling uses a systematic approach that divides the field into squares or rectangles of equal size (usually referred to as "grid cells"). Soil samples are collected from within each of these "cells." The location of each "grid cell" is usually geo-referenced using global positioning system technology. This method is used when variability of soil pH and immobile nutrients within fields cannot be easily identified.

However, soils in our area do not change in squares. Zone sampling uses a more subjective and intuitive approach to divide any field into smaller units. Soil samples collected at random from within each zone are bulked together and analyzed to provide an average sample value for each unit. This approach assumes that variability of soils within a field can be easily identified. The Veris Electrical Conductivity (EC) meter, aerial or satellite photography, and multi-year yield maps can be used to divide production fields into management zones. Information from a yield monitor is essential in identifying zones that should be sampled separately. As with the grid system, sampling points can be geo-referenced.

The "grid" sampling strategy can be used for the following conditions: 1) a measure of non-mobile nutrients is the primary concern; with no movement, distribution will be affected less by topography and other fixed properties; 2) management practices used in the past will override natural variability; and 3) there is a history of manure use.

The criteria that would favor the use of zone sampling are: 1) cost of sampling and analysis is a major concern; zones may be larger than grid cells thereby lowering sampling costs; 2) a measure of mobile nutrients is the primary concern; and 3) there is no history of manure application. Return to top.

Variable-rate center pivot irrigation

In all parts of the U.S., agriculture is putting increased demands on limited water resources. Yet, in our rural and farm communities, efficient water use is critical for sustainable economic development. Many states are currently developing management plans for water use within and between states. Nationwide, there are over 150,000 center pivot (CP) irrigation systems, watering over 21 million acres of cropland. However, recent drought periods and lawsuits between states have prompted a renewed interest in water conservation methods. In some areas, limits are already being placed on agricultural irrigation.

CP irrigation systems usually apply a relatively uniform amount of water to inherently variable fields. The variable nature of afield may result from any combination of factors such as variable soil types, topography, The University of Georgia VR Center pivot system or multiple crops. In addition to variability, CP irrigation is complicated by irregularly shaped fields, overlapping CP systems, etc. The solution lies in matching field variability with an equally variable irrigation application. The technology to do this is known as variable-rate irrigation (VRI).

Variable rate irrigation (VRI) technology works by applying irrigation water based on specific water needs of individual management zones, rather than applying a uniform rate across an entire field. By optimizing water application, the use of VRI can potentially save millions of gallons of irrigation water while increasing both crop yield and quality. The VRI system, developed at the University of Georgia, was commercialized by Farmscan in the fall of 2004. Hobbs and Holder, LLC, the US dealer for Farmscan, has to date installed 32 VRI systems onto a variety of center pivot systems from various manufacturers (i.e., Valley, Reinke, Zimmatic, and Gifford-Hill). These installations have taken place in Georgia, South Carolina, Florida, and Arkansas. Reasons for farmer interest in adopting VRI have ranged from environmental stewardship, conservation, economics, and productivity. Current VRI systems are installed on farms that grow traditional row crops (peanuts, cotton, and corn) as well as less conventional crops (i.e., turf). For these 32 installations, the average pivot size was 1463 ft (155 acres) with 138 of those acres cropped and 17 acres non-cropped. Although the average installation cost was $21,379.00, because cost-share assistance was provided through federally funded grants the average cost to the farmer has been only $5,345, or $34 per acre.

Clemson University has developed a variable-rate lateral irrigation system for site-specific application of water to match crop needs. This system could monitor and apply water based on the actual soil moisture content, pan evaporation data, or the U.S. Climate Clemson VR Lateral Irrigation system Reference Network (CRN) data. Information from the moisture sensors (which are located in the field according to soil type), evaporation pan and CRN is acquired using wireless technology. A GPS receiver is used to determine the position of the lateral irrigation system in the field. Variable speed control system allows the overhead irrigation system to move quickly over wet spots and slow down over dry spots.