Cover crops survey analysis

Cover crops can slow erosion, improve soil, smother weeds, enhance nutrient and moisture availability, help control many pests, and bring a host of other benefits to farms across the country. For more than 20 years, NCR-SARE has supported projects by researchers, producers, and educators who are using this time-tested method of revitalizing soil, curbing erosion, and managing pests.

Cover crop adoption has been increasing rapidly in the last 5 years, with an estimated 1.5 to 2.0 million acres of cover crops planted in the U.S. in 2012. During the winter of 2012-13, the NCR-SARE program contracted with the Conservation Technology Information Center (CTIC) to carry out a survey of farmers who have grown cover crops.  A short survey instrument of a dozen questions was developed with help from steering committee members of the Midwest Cover Crops Council.  The survey was distributed at several farmer conferences in the Midwest over the winter, and was also sent out in an online format to individuals across the U.S.

A total of 759 farmers completed the survey.  The farmers who completed the survey used cover crops on about 218,000 acres in 2012, and expected to increase that to over 300,000 acres in 2013.

Questions on cover crop adoption, benefits, challenges, and yield impacts were included in the survey.  Key findings included the following:

  • During the fall of 2012, corn planted after cover crops had a 9.6% increase in yield compared to side-by-side fields with no cover crops.  Likewise, soybean yields were improved 11.6% following cover crops.
  • In the hardest hit drought areas of the Corn Belt, yield differences were even larger, with an 11.0% yield increase for corn and a 14.3% increase for soybeans.
  • Surveyed farmers are rapidly increasing acreage of cover crops used, with an average of 303 acres of cover crops per farm planted in 2012 and farmers intending to plant an average of 421 acres of cover crops in 2013.  Total acreage of cover crops among farmers surveyed increased 350% from 2008 to 2012.
  • Farmers identified improved soil health as a key overall benefit from cover crops.  Reduction in soil compaction, improved nutrient management, and reduced soil erosion were other key benefits cited for cover crops.  As one of the surveyed farmers commented, “Cover crops are just part of a systems approach that builds a healthy soil, higher yields, and cleaner water.”
  • Farmers are willing to pay an average (median) amount of $25 per acre for cover crop seed and an additional $15 per acre for establishment costs (either for their own cost of planting or to hire a contractor to do the seeding of the cover crop).

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Automatic Steering of Farm Vehicles Using GPS

Autonomous guidance of agricultural vehicles is not a new idea, however, previous attempts to control agricultural vehicles have been largely unsuccessful due to sensor limitations. Some control systems require cumbersome auxiliary guidance mechanisms in or around the field while others rely on a camera

system requiring clear daytime weather and field markers that can be deciphered by visual pattern recognition. With the advent of affordable GPS receivers, engineers now have a low-cost sensor suitable for vehicle navigation and control.

GPS-based systems are already being used in a number of land vehicle applications including agriculture. Meter-level code-differential techniques have been used for geographic information systems, driver-assisted control, and automatic ground vehicle control.

Using precise differential carrier phase measurements of satellite signals, CDGPS-based systems have demonstrated centimeter-level accuracy in vehicle position determination  and 0.1˚ accuracy in attitude determination .

System integrity becomes impeccable with the addition of pseudo-satellite Integrity Beacons. The ability to accurately and reliably measure multiple states makes CDGPS ideal for system identification, state estimation, and automatic control. CDGPS-based control systems have been utilized in a number of applications, including a model airplane, a Boeing 737 aircraft, and an electric golf cart.

This paper focuses on the automatic control of a farm tractor using CDGPS as the only sensor of vehicle position and attitude. An automatic control system was developed, simulated in software using a simple kinematic vehicle model, and tested on a large farm tractor.

The primary goal of this work was to experimentally demonstrate precision closed-loop control of a farm tractor using CDGPS as the only sensor of vehicle position and attitude. This section describes the hardware used to do this.

Vehicle Hardware

The test platform used for vehicle control testing was a John Deere Model 7800 tractor (Fig. 1). Four single-frequency GPS antennas were mounted on the top of the cab, and an equipment rack was installed inside the cab. Front-wheel angle was sensed and actuated using a modified Orthman electro-hydraulic steering unit. A Motorola MC68HC11 microprocessor board was the communications interface between the computer and the steering unit.

The microprocessor converted computer serial commands into a pulse widthmodulated signal which was then sent through power circuitry to the steering motor; the microprocessor also sampled the output of a feedback potentiometer, the only non-GPS sensor on the vehicle, attached to the right front wheel. The 8-bit wheel angle potentiometer measurements were sent to the computer at 20 Hz. through the serial link.

GPS Hardware

The CDGPS-based system used for vehicle position and attitude determination was identical to the one used by the Integrity Beacon Landing System (IBLS). A four-antenna, six-channel Trimble Vector receiver produced attitude measurements at 10 Hz. A single-antenna nine-channelTrimble TANS receiver produced carrier- and code-phase measurements at 4 Hz. which were then used to determine vehicle position. An Industrial Computer Source Pentium-based PC running the LYNX-OS operating system performed data collection, position determination, and control signal computations using software written at Stanford.

The ground reference station  consisted of a Dolch computer, a single-antenna nine-channel Trimble TANS receiver generating carrier phase measurements, and a Trimble 4000ST receiver generating RTCM code differential corrections. These data were transmitted at 4800 bits/sec through Pacific Crest radio modems from the ground reference station, which was approximately 800 m from the test site, to the tractor.


Performing a valid tractor simulation required a good model of dynamics and disturbances. Ground vehicle models in the literature range from simple to complex, and no single model is widely accepted. The most sophisticated models are not always appropriate to use , especially since controller and estimator design require a simple, typically linearized, model of plant dynamics.

Kinematic Model

The simplest useful model for a land vehicle is a kinematic model, which is based on geometry rather than inertia properties and forces. Assuming no lateral wheel slip, constant forward velocity, actuation through a single front wheel, and a small front wheel angle, the latter two equations of motion can easily be derived.  The kinematic equations were derived in state-space form for ease of controller and estimator design. The state vector is composed of the lateral position deviation from a nominal path, heading error, and effective front wheel angle.

Steering Calibration

Initially, calibration tests were used to create two software-based “look-up” tables, one which linearized the output of the steering potentiometer versus the effective front wheel angle and the other which linearized the computercommanded wheel-angle rate to the actual wheel-angle rate. To calibrate the potentiometer readings of effective front wheel angle, steady turn tests were performed to find the heading rate (dY/dt) of the tractor at various potentiometer readings. For each test, the tractor was driven in a circular path with a constant front wheel angle and constant forward velocity while GPS heading data was taken and stored. By compiling all these tests, a function was generated that related steady-state heading rate to potentiometer reading.

Calibration of the commanded wheel angle rate was simpler. Constant steering slews were commanded by the computer at varying levels of actuator authority (u) while wheel angle data was taken and stored. The time rate of change of the effective wheel angle was later estimated for each steering slew.


The first controller designed, simulated, and tested on the tractor performed closed-loop heading. The computer code was written so a user could command a desired heading using a keyboard input. The computer would then send the appropriate commands to the electro-hydraulic actuator to track the desired heading. The first tests were closed-loop heading tests designed to verify the kinematic vehicle model. These initial tests also yielded a better feel for tractor disturbances.

Heading Controller Design

A hybrid controller was designed to provide a fast response to large desiredheading step commands. A non-linear “bang-bang” control law generated actuator commands when there were large errors or changes in the vehicle heading or effective wheel angle states. Typically, these large changes occurred in response to a large heading step command. When the vehicle states were close to zero, a controller based on standard Linear Quadratic Regulator (LQR) design  was used.

“Bang-bang” control is a standard non-linear control design tool based on phase-plane technique. Unlike linear feedback controllers, bang-bang controllers use the maximum actuator authority to zero out vehicle state errors in minimum time just as a human driver would. For example, in response to a ,commanded heading step increase of 90˚, a bang-bang controller commands the steering wheel to hard right, holds this position, and then straightens the wheels in time to match the desired heading. In contrast, a linear controller would respond to the step command by turning the wheels to hard right, then slowly bringing them back to straight, asymptotically approaching the desired heading.

The drawback to bang-bang control is that when state errors are close to zero, the controller tends to “chatter” between hard left and hard right steering commands. For this reason, a linear controller was used for small deviations about the nominal conditions.

Experimental Heading Results

During the heading tests, the tractor was driven over a bumpy field at a nearly constant velocity of 0.9 m/s. The driver commanded an initial desired heading and a number of desired heading step commands through the computer. The tractor tracked the commanded headings very accurately, even in the presence of ground disturbances. Figure 5 shows a plot of CDGPS heading measurements during the longest closed-loop heading trial recorded. Over about one minute, the mean heading error was 0.03˚ and the standard deviation was 0.76˚. From separate tests, the expected sensor noise was zero mean with approximately 0.1˚ standard deviation, so the true system heading error standard

deviation was almost certainly less than 1˚.

The rise time of the controller for this particular command (response for a 90˚ step in commanded heading ) was approximately 7 seconds, and the settling time was less than 10 seconds. An small overshoot of about 4˚ occurred at the end of the heading step response.


After performing closed-loop heading, the next step toward farm vehicle automation was straight-line tracking. These series of tests were designed to simulate tracking a row. To track a straight line, vehicle position was fed back to the control system along with heading and effective wheel angle.

Line Tracking Controller Design

As in the closed-loop heading case, the line tracking controller was implemented as a hybrid controller with various modes. To get the vehicle close to the beginning of the “field” and locked on to each line or “row”, a coarse control mode was used based on the closed loop heading controller described above. Once a line was acquired, a precise linear controller based on LQR techniques took over.

Experimental Line Tracking Results

Two line-tracking tests were performed on the same field as the closed-loop heading experiments. The vehicle forward velocity was manually set to first gear (0.33 m/s), and the tractor was commanded to follow four parallel rows, each 50 meters long, separated by 3 meters. Throughout these tests, the steering control for line acquisition, line tracking, and U-turns was performed entirely by the control system. CDGPS integer cycle ambiguities were initialized by driving the tractor as closely as possible to a surveyed location and manually setting the position estimate.

In fact, there was a small, steady position bias (about 10 cm) between the two trials due to the unsophisticated method that was used for GPS carrier phase integer cycle ambiguity resolution. A more sophisticated method involving pseudolites or dual frequency receivers would have eliminated this bias and is a topic of future research.

Since the plots show CDGPS measurements and not “truth”, they represent the error associated with the control system and physical vehicle disturbances. The tractor controller was able to track each straight line  with a standard deviation of better than 2.5 cm., the vehicle lateral position error never deviated by more than 10 cm, and the mean error was less than 1 cm for every trial.


This research is significant because it is the first step towards a safe, low-cost system for highly accurate control of a ground vehicle. The experimental results presented in this paper are promising for several reasons. First, a farm tractor control system was demonstrated using GPS as the only sensor for position and heading. Only one additional sensor—the steering potentiometer—was used by the controller. Second, a constant gain controller based on a very simple vehicle model successfully stabilized and guided the tractor along a straight, predetermined path. Finally, it was found that a GPS controller could guide a tractor along straight rows very accurately. The lateral position standard deviation was less than 2.5 cm. in each of the 8 line tracking tests performed Transitioning from automatic control of a lone farm tractor to automatically controlling the same tractor towing an implement is a large step since the

combined system will have more complex dynamics and larger physical disturbances acting on it. Guiding a vehicle along curved paths will also present a challenge that has not been addressed. This work describes a control methodology that was successfully employed to control a real farm tractor to high accuracy. This same methodology, combined with a more sophisticated dynamic model may be sufficient to control the more complicated tractor-implement system. Further research is currently underway to explore this possibility.

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PA systems offer increased versatility

 There are precision ag products available now that allow operators to choose a steering system to suit their individual operation, while still having the capability to do field coverage mapping  and variable rate seeding. Farmers can also monitor implements on the go using up to four external cameras.

“Farmers can choose from a range of steering options including manual guidance, assisted steering and full autopilot whereby the tractor virtually steers itself.” says Ross Johansson, Brand Manager, AFS Precision Farming and Guidance. “We have the FM-1000 unit which is Real Time Kinetic (RTK) compatible to provide steering accuracy to within 2-cm which is ideal for farmers working in tramlining or controlled traffic environments.”

A range of seven steering patterns are available from curves to spirals and industry exclusive free-form steering. Operators can set the system to work in virtually any field condition, regardless of obstacles or unique field conditions. Steer the tractor, the gear or both The FM-1000 contains two GPS receivers which give farmers greater choice when it comes to steering both the tractor and implement. The first GPS receiver controls the tractor’s steering, while the second controls the implement steering path.

Operators can monitor the individual path of the tractor and implement. If they find the implement is steering along a different path due to field conditions or skew for example, they can program the system to steer the tractor off-line and maintain the implement only on the set guidance path. There is also the option to set the steering to keep both the tractor and implement on the guidance path, which is ideal for applications requiring a high degree of steering accuracy.

The design of the GPS receiver on the FM-1000 enables it to pick up a broad range of satellite networks known as the Global Navigation Satellite System, thereby reducing the chance of signal dropout. Signal drop out can be caused by a range of different interferences including solar flares which are forecast to increase in coming years. Solar flares are caused by explosions in the sun’s atmosphere and have the ability to interrupt GPS signals. By accessing a greater range of satellites, the risk of potential signal drop out is minimised, allowing farmers to keep on farming, accurately and reliably, with reduced down-time. The FM-1000 unit is also interchangeable between equipment and can be used across a broad range of equipment platforms, allowing farmers to maximise their investment in the technology.

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Precision Farming Tools

GPS: Its Uses and Potential Are Growing

Global positioning systems (GPS) are widely available in the agricultural community. Farm uses include:

•mapping yields(GPS + combine yield monitor),

• variable rate planting (GPS + variable rate planting system),

•variable rate lime and fertilizer application (GPS + variable rate controller),

•field mapping for records and insurance purposes (GPS + mapping software), and

•parallel swathing (GPS + navigation tool).

For a review of the principles of GPS to locate specific field points, refer to this GPS Tutorial (Trimble Navigation Limited, 2008). GPS and associated navigation systems are used in many types of agricultural operations. These systems are useful particularly in applying pesticides, lime, and fertilizers and in tracking wide planters/drills or large grain-harvesting platforms.

GPS navigation tools can replace foam for sprayers and planter/drill-disk markers for making parallel swaths across a field. Navigation systems help operators reduce skips and overlaps, especially when using methods that rely on visual estimation of swath distance and/ or counting rows. This technology reduces the chance  of misapplication of agrochemicals and has the potential to safeguard water quality. Also, GPS navigation can be used to keep implements in the same traffic pattern year-to-year (controlled traffic), thus minimizing adverse effects of implement traffic.

Use of GPS navigation in agrochemical application with ground equipment has grown rapidly, and commercial applicators are quickly adopting the tool. According to a 2007 survey of those who offered custom application (Whipker and Akridge, 2007), 82 percent applied at least some of the fertilizer/chemicals using a GPS navigation system with a manual-control/light bar  guidance system. Twenty-nine percent said they used a  GPS navigation system with an auto-control/auto-steer guidance system for at least some of their custom application. On average, for all custom applied materials, percent was applied with GPS light bar, and 12 percent was applied with auto-steer GPS. GPS navigation has  become standard practice for U.S. aerial applicators. Crop producers are also starting to adopt these systems, because GPS navigation is an excellent way to improve accuracy, speed, and uniformity of application.

Why are navigation systems important to field operations?

Automated guidance of agricultural vehicles (tractors, combines, sprayers, spreaders) has been motivated by a number of factors—most important is to relieve the operator from continuously making steering adjustments while striving to maintain field equipment or implement performance at an acceptable level. This is not surprising, considering the many functions an operator must monitor, perform, and/or control while operating the vehicle.

The requirements placed on farm-equipment operators have changed drastically with increases in equipment size, power, multiple equipment functions, and speed—as well as monitors reporting on specific system performance. These increasing demands on the operator can result in increased errors in function, costs, environmental problems, and operator fatigue.

Foam markers, a widely used technology

Foam markers are the most common form of navigation aid used during fertilizer and pesticide application. The foam is dropped and used to align the applicator during the return pass. Foam markers utilize an air pump to pressurize a tank containing the foaming agent. The pressurized fluid causes the foaming agent to flow into an accumulating chamber. The foam collects in this chamber until the accumulated mass overcomes surface tension, causing a foam blob to fall to the ground.

Most often the foam accumulators are placed at the ends of the applicator boom or, alternately, at the center of the applicator when booms were not utilized, as in the case with spinner-disk granular applicators. Equipment operators use the foam blobs left on the field surface as a navigation aid to know where the applicator has passed.

GPS + Navigation Aids

Relatively inexpensive navigation aids known as parallel-tracking devices assist the operators to visualize their position with respect to previous passes and to  recognize the need for steering adjustments. These aids are commercially available in several configurations. One system is a light bar, which consists of a horizontal series of Light Emitting Diodes (LEDs) in a plastic case 12 inches to 18 inches long. This system is linked to a GPS receiver and a microprocessor. The light bar is usually positioned in front of the operator, so he or she can see the accuracy indicator display without taking their eyes off the field. The light bar can be mounted inside or outside of the cab, and the operator watches the “bar of light.” If the light is on the centerline, the machine is on target. If a bar of light extends to the left, the machine is off the path to the left and needs to be corrected. In like manner, if a bar of light extends to the right, the machine is off to the right.

Software allows the operator to specify the sensitivity to and distance between the swaths. Similar GPS  navigation systems have been used for aerial application since the early 1990s. Also, the GPS system gives the current location of the implement and, with past traffic patterns, the computer interface provides the operator directions to maintain proper swath width to  match adjacent traffic paths. If an operator leaves the field to refill the applicator or is forced out of the field due to weather, upon return, the operator can resume and maintain accurate swath widths, and over-spraying on previous sprayed areas is eliminated. More advanced systems have a screen showing the swath of the machine a sit moves through the field (Figure 2). Early models only allowed straight-line parallel swaths, but current models are available for any contour traffic pattern. Areas covered with previous swaths are indicated on the screen. The advanced navigation system coupled with a variable rate spreader drive and  software has the capacity to generate “as-applied” maps showing previous coverage and the application  pattern. This provides an excellent record of the pattern and timing while operating in the field. Portions of the field that are not treated, such as wet areas, can be marked in the computer and stored for later operations when conditions permit application. All of this is done without having to physically mark the field area with flags.

GPS + Auto-Steer Navigation

More advanced navigation systems (auto-steer systems) possess similar capabilities as the navigation aids and also have the additional option to automatically steer the vehicle. Auto-steering is accomplished with a device mounted to the steering column or through the electro-hydraulic steering system. The accuracy level of these system is based on the quality of differential correction and internal data processing: as the accuracy improves, the corresponding cost increases. These navigation systems are classified in three categories:

Submeter accuracy usually means approximately  two feet to four feet year-to-year, and less than one foot pass-to-pass errors. The differential correction source could be from a Coast Guard beacon, WAAS (Wide Area Augmentation System), or satellite providers. These systems are relatively inexpensive (about  $6,000 to $15,000) and can be used while performing tillage, some types of fertilizer and chemical applications, seeding, and harvesting. These devices can be easily transferred between vehicles, so the same steering system can be used on different vehicles. However, operations requiring highly accurate guidance are not feasible with submeter level equipment.

Decimeter accuracy provides approximately four inches to eight inches year-to-year and three inches to  five inches pass-to-pass errors. This can be achieved using either a local base station or dual frequency receivers with private satellite differential correction subscription. With the increased performance, operators can use auto-steering during most of the conventional field practices. Prices range from $15,000 to $25,000 plus the satellite subscription (up to $1,500 annually).

Centimeter accuracy can be obtained by using a local  base station with the real-time kinematic (RTK) differential correction. Both long-term and short-term errors (of approximately one inch) have been reported for these systems. Vehicles equipped with this high level 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 (see “Additional Features” for definitions). The price ranges from $40,000 to $50,000 with no annual subscription fees.

GPS Navigation vs. Foam Markers

Potential advantages of GPS Navigation (GN) relative to foam markers for agricultural applications include:

• GN is more reliable and more accurate than foam  markers. Using foam markers could cause about 10 percent of the field to be skipped or overlapped. With the GN, the skip and overlap rate drops to about 5 percent. Some tests have shown that with an experienced operator, the skip and overlap rate can be as low as 1.5 percent.

• GN allows accuracy at higher speeds. GPS navigation can attain a 13 percent to 20 percent higher speed than a foam marker (Buick and White, 1999). Naturally, an increase of speed is terrain dependent. If field conditions limit speed, then a GN benefit is unlikely.

• GN is a possibility with spinner spreaders. Foam markers are not generally used with spinner spreaders. The spreaders have no boom on  which the foam equipment can be installed. Due to the spread width, a foam marker in the center of the machine path is difficult to see from the next swath, and the driver would still be using a visual estimate  for the spreader swath.

• GN is easy to use. Anybody can learn to use GPS navigation systems, regardless of computer skills. The systems require only a little practice—typically about 30 minutes.

• GN provides effective guidance over growing crops. With solid-seeded crops, foam tends to fall through the canopy to the ground where it is almost invisible, contributing to skipping or overlapping. Crop height does not affect GPS.

•  GN allows operation when visibility is poor. GN works at night, in dust, or in fog. This lengthens working time during critical planting and spraying periods. In many areas, nighttime is best for spraying because of low wind speed. Leaf orientation changes at night and herbicide may or may not be as  effective as during daylight(check with local Extension specialists). Nighttime spraying of insecticides can protect sensitive bee colonies.

• GN is less affected by weather. In certain conditions such as low humidity, heat, and large fields, foam markers can be rendered ineffective. The foam can evaporate before the operator makes the return swath. GN works at any temperature, including low temperatures when foam systems freeze.

• GN has lower recurring costs. GN has no moving  parts or tubes to clog. Depending on the manufacturer, software updates are usually free to system owners. Foam-marker systems require foam, dye, and tank cleaner.

The primary recurring cost for GPS navigation is satellite differential correction. Typically, the subscription costs $600 to $1,500 per year for each GPS unit. Many producers already have GPS for yield monitoring and may subscribe for differential correction. For them, GN has almost no recurring costs. In many areas of Virginia, it is possible to use the Coast Guard beacon or WAAS for GPS differential correction. These services are free and may be adequate for some applications, including dry fertilizer with a spinner spreader.

Accuracy for spraying should be within six inches(10 centimeters); the GPS equipment supplier can provide information regarding the differential correction needs for a specific location. For more on GPS systems, review Precision Farming Tools: Global Positioning  System (GPS), Virginia Cooperative Extension (VCE).

•  GN reduces operator fatigue and eye strain. With  the light bar mounted directly in front, GN operators do not need to look backward or sideways. They can drive accurate swaths while looking straight ahead.

• GN has lower setup time. Foam markers require that tanks be filled and dyes be changed. GN begins workingapproximately30secondsafterthemachine is switched on.

• GN is not affected by wind or boom bounce.  Blowing foam or a foam system bouncing over rough ground at the end of a long boom may introduce substantial error. GPS systems are not affected by rough terrain or wind.

• GN reduces pesticide use by reducing overlaps.  If a 10 percent overlap is reduced to 5 percent, pesticide use also is reduced by 5 percent. The same is true for fertilizer and seed, so using GN is better for the environment and good for the bottom line.

• GN reduces the need for people to enter already  sprayed areas. The operator can mark where spraying stopped without dismounting.

Additional Features

Decisions about adapting GPS navigation should be based on particular farm needs, farm operation procedures, and understanding of positioning errors. Such issues as vehicle dynamics, tracking of trailed implements, and field terrain also need to be considered. Proper alignment and installation of the GPS navigation system is required for effective field operation. Poor quality of the steering-control systems, a sloped terrain, or misaligned implements will cause the field performance of GPS navigation to suffer. An important feature of GPS navigation systems is the ability to follow particular traffic patterns and provide effective feedback so that the operator or auto-steer system can appropriately respond. Most systems can  effectively perform straight-line patterns(linear swathing), and many can follow contours and other field features.

Although most GPS navigation systems are designed specifically for the task of vehicle steering, some systems have features to collect spatial data (such as application maps and yield maps) or to operate variable-rate  controllers. Additional features spread the cost of the system among several tasks while increasing efficiency in multiple areas of the crop production program. The documentation provided by a GPS system could be  used to show that the product or field work was applied in specific locations at a specific time. Setbacks specified by regulatory agencies and other sensitive areas (such as ornamental crops, nurseries, gardens, schools, and residential areas) may be defined as “no-apply zones.” The “as-applied” map includes areas in which  application occurred and rates can be recorded. It is possible to include not only position, but time and date information in an application record as well. Such documentation could be used for accurate recordkeeping for agrochemical application and machine operation and, potentially, for regulatory and legal defense purposes.

GPS navigation products are distinguished by the compactness of their components and user interfaces. Some systems cause technical challenges during installation  and calibration, while others may be functional in less than an hour. User interfaces range from intuitive, colorful, graphic touch-screen displays to hard-key menus with limited graphics feedback.

A sloped terrain makes control of vehicle dynamics challenging. Roll (tilt from side-to-side), pitch (movement from front-to-rear), and yaw (rotation around the vertical axis) alter the GPS antenna location with the  projected center of the vehicle . For example, when driving across a slope, the horizontal position of the GPS antenna is downhill with respect of the center of the vehicle, and the guidance will be in error down the slope. To compensate, some systems include gyroscopes, accelerometers, or additional GPS antennas. Less advanced terrain-compensation modules deal with only roll and pitch angles of the vehicle, while others can measure total dynamic attitude in six  degrees of freedom and enable the system to compensate for variable terrain.

Several manufacturers have add-on implement steering systems for proper implement tracking. Compensating for known geometry of the tracking from implements can be adjusted with the vehicle’s trajectory to keep the implement aligned. Optical and crop-based tracking systems can be useful when positioning implements with respect to established rows.

Bottom Line

GPS navigation has many advantages over conventional marking devices such as foam markers, and especially over the visual-estimation method for spinner spreaders. With an existing GPS being used for yield monitoring or field mapping and soil sampling, the GPS navigation system can increase the efficiency of the farm or agribusiness while minimizing adverse environmental impacts associated with overlapping  applications. The system can also reduce operator  fatigue and anxiety regarding fertilizer and pesticide application. Finally, use of this technology can demonstrate to the nonagricultural community that advanced  technology is being used to farm efficiently and safely.

The advantage of “as-applied” maps, provided by some systems, is documentation that applications were made at the appropriate location and rate.

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From GPS to GNSS


Global Positioning Systems (GPS) are satellite-based  navigation systems that utilize a network of earth orbiting satellites. GPS operates well under any weather condition  and does not require a subscription fee. GPS is a crucial component of precision agriculture by providing precise  location information with very high repeatability. In recent years, GPS have improved in their level of  performance and functionality in part because new GPS receivers can track satellites not only from the 32 NAVSTAR  satellites of the United States but also from the Russian  GLONASS (approximately 24 satellites) systems. These high-accuracy navigation and positioning technologies are  categorized as a GNSS (Global Navigation Satellite System).

We anticipate that even higher levels of performance will be  achieved when the Galileo satellite constellation (European Union) becomes available in 2014 with an initial operating  capacity of 18 satellites and expanding to 30 satellites by the year 2020. The changing technology motivates the need for  precise definitions.

It is clear that GPS will continue to have a remarkable impact on production agriculture. Vehicle guidance or automatic steering control has been the most commonly adopted GPS technology among growers in the last five years. Every year new and improved navigation systems become available with a range of precision capacities to fit most mechanical operations and with new functional capabilities. This publication describes the latest trends in GPS technology and elaborates on topics of extra functionality such as variable rate application, land leveling, and yield monitoring; all are now available from the cab mounted display interface. Key operational parameters of GPS receivers

Important operational parameters of GPS receivers include accuracy, correction service, and hardware selection. These technical aspects are explained in detail by our earlier publications (Andrade-Sanchez and Heun (2010 and 2011)) AZ1558 January 2012 with particular emphasis in application in Arizona. The user must carefully select between multiple options in order to obtain satisfactory performance when implementing this technology in mechanized operations.

Accuracy. GPS receivers are built to achieve certain accuracy levels depending on their internal components, enabled communication protocols, and unlocked capabilities in firmware. Accuracy is perhaps the single most important factor; therefore it is worth checking the manufacturer’s claims on pass-to-pass and year-to-year accuracy. Remember that GPS costs are related to their accuracy levels, so it pays to do a careful analysis of accuracy needs in your farm.

Differential Correction. This is an essential function of modern GPS receivers that is needed to obtain adequate levels of accuracy for machine applications. Most agricultural applications require sub-meter (less than 3 ft) pass-to-pass accuracy, but very often accuracy is needed as close as a few inches and even at sub-inch level. Correction services in the U.S. such as Wide Area Augmentation System (WAAS) are available free of charge. Private firms such as OMNI-Star and John Deere provide excellent services to subscribing clients by charging fees according to the accuracy levels.

When selecting a particular GPS receiver, it is important to consider whether it comes loaded with WAAS or OMNIStar capabilities, and to confirm that the receiver can be upgraded to perform at higher levels of accuracy (RTK).

Real-time kinematics (RTK) is the most accurate GPS  correction system used in agricultural applications. Growers using RTK GPS need access to a ground base station through radio link. Users can choose to buy their own base station or subscribe to a local network of RTK signal correction stations. Subscribing to an existing station makes good economic sense if it is available in the area. Both options are very common in Arizona and in the near future we expect that more will become available. The Department of

Transportation (DOT) is currently working in some states to provide wide-range coverage of RTK-level correction signals  through their Continuously Operating Reference Stations (CORS) system. There is much potential of widespread use of RTK correction under the CORS infrastructure. A model of application of CORS to agriculture has been tested in the  state of Alabama (Winstead et al., 2009). Private providers are testing the delivery of correction signals through cellphone modems.Hardware Selection. One aspect often ignored is the selection of the external antenna that has to match the capabilities of the receiver. Newly released integrated GPS systems require dual-frequency antennas to track L1 and L2C satellite signals.

Enhanced GNSS systems

One way to present the improvement of these GNSS systems over GPS alone is to compare the level of dilution of precision (DOP) over the course of a day between the systems. DOP is a dynamic parameter that is affected by changes in satellite number and geometry with major implications for vehicle navigation. Higher DOP values translate to higher uncertainty of positioning and can result in agricultural operation down-time and lower productivity when auto-guidance is required for an operation.

Integrated Systems

The advances in computer hardware/software of the last two decades are evident in the design of new agricultural machines in which some mechanical controls have been replaced with computer-controlled systems of enhanced functionality. Electronic systems and computer displays are now a common scene in the cab of the tractor/sprayer or other power unit used in agriculture. Earlier versions of these displays were designed as to perform a single operation or series of operations of the same kind; this is the case for rate controllers for spraying systems, and early auto-steer displays. New versions of computer displays are capable of performing multiple functions from the same interface and reduces cab clutter. These integrated systems are the latest in off-the-shelf technology for precision agriculture.

Multiple active windows enhance operation. Video cameras can be connected for better view and safe monitoring of equipment operation through live video. Active screens can be recorded and saved as screen-shots in electronic image formats such as PNG (portable network graphics).

Operating system. Upgradeable. Menu interface is available in multiple languages.

Multi-function. State-of-the-art computer processors allow these displays to handle all levels of navigation (steering control); application of multiple products and variable-rate of a single product; seeding rate control; yield monitoring; vertical position control for bucket blades performing landleveling, etc. Input/Output serial ports allow connection with the hardware required in each application. After the job is completed, these systems can generate job reports and export them in pdf format to maintain records of input utilization, field productivity, etc.

Integrated GPS receivers. These GPS receivers use double frequency antennae to link LANDSAT and GLONASS satellites. Some of them have dual receivers to activate position monitoring of the implement.

USB. For uploading of operating system upgrades, and shape files (SHP) for navigation A-B lines and input prescription files. These ports allow downloading of yield, machine performance data, maps of as-applied inputs, error messages, screen-shots, etc.

External communications. Through radio and/or modem, this enables over-the-air data transmission and GPS signal correction. These systems can function as nodes in wireless networks. These displays are ISO-ready, which means that they can function in Virtual Terminal (VT) mode through ISO-11783 (ISO-bus) standard communication protocol to enable universal communication with implements, in particular, planter and sprayer controllers.

Functionality of these integrated systems

Steering control

The level of steering control applicable will depend on the level of work to be done and the machine itself. Light-bar type guidance systems use differential correction level GPS to track the vehicle position and then send signals to arrays of LED’s to help the driver find the track to follow for the particular application. These devices are inexpensive and helpful in some applications where sub-meter accuracy is acceptable. However, they can require just as much of a driver’s attention as traditional methods when a high level of precision positioning is required. If a higher level of accuracy (< 3ft) is needed, a hands-free steering system is in general a better way to go.

Hands-free auto-steering systems are guidance and control systems that take over a machine’s steering system. They allow the driver to place more attention on vehicle/implement performance rather than to driving a straight line. Less expensive systems typically consist of an electric servomotor connected directly to the steering wheel.

Although these steering wheel motor systems work well, they can take up a lot of space on smaller tractors but are often the only choice. If the tractor has a hydraulic steering system (no mechanical connection between the steering wheel and front axle), a solenoid valve can be installed in the hydraulic lines outside of the cab. This tends to be a much cleaner way of tapping into the steering system and works well with the more complex guidance systems. In addition to RTK level GPS, these auto-pilot systems need positioning sensors such as gyroscopes and accelerometers to achieve the highest level of navigation performance. These systems are connected to the computer display to perform their navigation functions.

Variable rate and section control for chemical applications and seed planting

Variable rate technology is at the heart of precision farming technologies because, in contrast to the uniform application, variable-rate functions set the stage for implementation of site-specific management of production inputs. All integrated displays have variable-rate functions based on prescriptions previously loaded. In order to perform variable-rate application functions, these systems need to interpret prescription maps that contain information on the field distribution of application rates. GPS information is used to find the tractor/sprayer location in the field and then a signal is sent to the rate controller,  setting a particular rate. It is important to mention that at this level of hardware integration, these displays send GPS based speed information to the rate controller to adjust the flow of chemical according to travel speed.

Another mode of operation available in some of these integrated displays is variable rate application based on real-time data acquisition of crop conditions. This mode of operation requires serial communication with spectral crop sensors and is particularly challenging because the system needs an algorithm to convert the sensor signal into an application rate. Significant advances have been achieved in this area but crop algorithms are still being developed and tested by the scientific community engaged in sensor-based management.

 Along with variable rate solutions comes section control that is applied to planting and chemical application operations. Detailed information on the use of automatic section control for spinner-spreaders, sprayers, and planters has been described by researchers from Alabama A&M and Auburn Universities (see Fulton et. al., 2010, 2011-a, 2011-b).

In the context of seed planting, section controllers are used to shutoff the delivery of seeds in areas of the field already planted. This section control can be implemented at the level of each individual planter unit or by whole sections by installing electrical or pneumatic clutches on the drive shaft of the planter. On the other hand, section control in applications of liquid chemicals, either sprayed or injected, refers to the ability of the system to shut-off sections of the spraying boom or injection-knife sections in order to avoid overlapping applications. The red line in the map indicates the autopilot function; the input rates on the right indicate the ability of the system to handle this information. In terms of section control, the icon representing the tractor/sprayer shows with green color that only the right section has been enabled while the middle and left sections (in red) are disabled). These functions are simultaneously implemented in the field at  the time of application.

Yield Monitoring

All of the multifunction displays can handle yield monitoring functions. The benefits of system portability become evident since harvest is carried out at the end of the season. In Arizona, the crops with the highest potential for the implementation of yield monitoring technology are cotton and small grains. There are commercially available yield monitoring systems that can be used to retrofit harvest machines. In the case of cotton, yield is determined by measuring the mass flow rate of seed cotton as it travels from the headers to the rear basket. The sensors used for these measurements can be of two types: optical sensors that measure light attenuation caused by the flow of seed cotton, and microwave sensors that use the Doppler effect principle when the energy emitted by these sensors is reflected by the flow of cotton. In the case of small grains, yield monitors measure the impact force of the flow of grain in the grain elevator over a plate instrumented with a force transducer. There is a proportional relationship between the force of impact and the flow of grain.

To obtain yield data of absolute quality, careful calibration of flow sensors should be repeated at least three times during the harvest season. Yield information within the field allows growers to grasp the extent of variability and stimulates a process of determining the factors driving field variability. Based on the analysis of yield data, growers can develop their own improved management strategies to adjust practices that could potentially sustain or increase yield levels and product quality with reduced input.

Land leveling

Now that we have sub-inch accuracy and control in the horizontal plane, what about the vertical plane? With the addition of the GLONASS constellation to the RTK system, elevation positioning is better than ever. Manufacturers such as Trimble, Topcon, and John Deere have integrated land leveling functions into their new tractor displays. Fields can be surveyed, mapped, designed, and leveled entirely from inside the tractor. RTK GPS equipment replaces the external laser leveling systems normally used. A dual antenna system is used to monitor the height of the scraper blade and hydraulic modules are added to control the flow of fluid that sets the blade’s position. This added functionality can eliminate problems associated with gusting winds moving the laser tower.


The integrated systems described in this publication represent the newest development in advanced systems for enhanced functionality of machines in production agriculture. As expected, these systems will keep evolving to improve their performance. Active competition between manufacturers will also result in affordable quality products that will benefit growers in their transition from conventional to more advanced systems. Two operational elements of these computer-display systems that are worth analyzing are their portability, which can be a money-saving attribute when many power units can share at least part of the new components. The other element is that the use of these new displays requires computer skills and therefore workforce training is an essential element of modern farm management systems to enable full utilization of this technology.

This extension bulletin is designed to be of an informative nature, and along with other publications in this series prepared by the Research and Extension Program in Precision Agriculture at the University of Arizona, we expect to help growers make informed decisions as they embark in the implementation of precision farming solutions. It is recommended that growers consult with equipment dealers to obtain specific information on system compatibility, upgrade options, and service.

( Source

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Satellites as a bridge to new agronomic era

Nowadays it is hard to impress somebody with satellite launching. Though just 60 years ago it was like a fantastic tale. Nobody thought that it can be possible to see the photos of your house, street or field made from the space. In this article the issue of modern achievement, which became available thanks to satellite systems  and their influence on agrarian business will be discussed.

Achievement 1. Navigation.

Due to satellites the system of navigation GPS, which is now used for determination of  location and direction on air (aircrafts), on water (ships), and on land became possible. An advantage of this system is that it provides opportunity for any place (excluding polar region), almost in all weather conditions, to indicate the speed and  objects location. The basic principle here – the determination of the location by measuring the reception time of the synchronized signal from satellite to the consumer.

Achievement 2. Weather and climate control.

Satellites give possibility to explore the weather around the world, allowing them to follow the effects of phenomena like volcanic eruptions and burning gas and oil fields.

Satellites are the best sources of data for climate changes research. Satellites monitor ocean temperatures and prevailing currents; rise/drop of the sea levels, the changing sizes of glaciers. Satellites can determine long-term patterns of rainfall, vegetation cover, and emissions of greenhouse gases.

Achievement 3. Land Stewardship

Satellites can detect underground water and mineral sources; monitor the transfer of nutrients and contaminants from land into waterways, and the erosion of topsoil from land. They can efficiently monitor large-scale infrastructure, for example fuel pipelines that need to be checked for leaks.

As we can see, satellites have changed both: our leisure time and business, provoked the emergence of new agricultural technologies. We got possibility of more accurate prediction of changes in climate and weather, which is very important for farmers. Satellites have made possible simplification and improvement of the process of soil nitrogen saturation. We would like to highlight the following:


You can equip the tractor with signal receiver GPS, heading sensor and controller – the screen that reflects the identity or deviation from the path of the tractor predetermined. The control system allows you to store and forward rate tractor strictly parallel to the line that is fixed on the first pass of the unit, the second option – autopilot, which consists of electro-hydraulic automatic control of the tractor, which provides tractor autopilot on the field. Tractor-driver helps the process only while cornering, allowing it to focus on the process and less physically tired.

GIS (Geographic information system) – the system of collection, storage, analysis and graphical visualization of spatial (geographical) data and related information on the necessary facilities.

A new and promising directions in agriculture abroad is precision agriculture. The concern is that to use the heterogeneous data (the geographically-referenced results of soil sampling, remote sensing data processing, digital thematic maps) to optimize decision-making on the local application of fertilizers and pesticides into the soil to boost agricultural productivity.

2. Satellite crop monitoring

Technology based on spectral analysis of high resolution satellite crop images which enables to monitor vegetation developments, soil temperature,  humidity and to reveal problem areas on the field. Satellite crop monitoring is also suitable to precise weather forecast based on concrete field coordinates and to recall historical weather data retrospection. Discrepancy in NDVI dynamics reports about the disparities in development within a corn or a field that indicates the need for additional agricultural activities in some areas.

In conclusion, we can say that due to modern technologies as satellites we construct our future, and in order to go with the times it is very important to know about them and to use them, because combination of them with your experience make your business more efficient and with less time and effort costly.

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Lamborghini Announced Nitro Tractor

Lamborghini’s tractor division has recently unveiled the 2013 Nitro described as a stylish and powerful tractor.

Styling is certainly on the bottom of the list when buying a tractor but for the very few who want to look good while working, Lamborghini Trattori has come up with the Nitro. Giugiaro was in charge of designing this medium power tractor which features double LED taillights and a lowered contour hood.

The spacious and comfy interior cabin provides a 360-degree visibility thanks to the panoramic, convexly-mounted windows made from athermal glass. Power comes from four-cylinder Deutz Tier 4i engines connected to a fully mechanical five-gear system or a three-speed Powershift.

Stopping the tractor are independent oil-immersed disc brakes and a servo-assisted braking system. As standard, the Nitro has a Park Brake system while for more money it can be fitted with a Steering Double Displacement steering pump which will reduce the number of steering wheel turns for quicker maneuvers.

(Source: Lamborghini)

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Potential Long-Term Benefits of No-Tillage and Organic Cropping Systems

There have been few comparisons of the performance of no-tillage cropping systems vs. organic farming systems, particularly on erodible, droughty soils where reduced-tillage systems are recommended. In particular, there is skepticism whether organic farming can improve soils as well as conventional no-tillage systems because of the requirement for tillage associated with many organic farming operations. A 9-yr comparison of selected minimum-tillage strategies for grain production of corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and wheat (Triticum aestivum L.) was conducted on a sloping, droughty site in Beltsville, MD, from 1994 to 2002. Four systems were compared: (i) a standard mid-Atlantic no-tillage system (NT) with recommended herbicide and N inputs, (ii) a cover cropbased no-tillage system (CC) including hairy vetch (Vicia villosa Roth) before corn, and rye (Secale cereale L.) before soybean, with reduced herbicide and N inputs, (iii) a no-tillage crownvetch (Coronilla varia L.) living mulch system (CV) with recommended herbicide and N inputs, and (iv) a chisel-plow based organic system (OR) with cover crops and manure for nutrients and postplanting cultivation for weed control. After 9 yr, competition with corn by weeds in OR and by the crownvetch living mulch in CV was unacceptable, particularly in dry years. On average, corn yields were 28 and 12% lower in OR and CV, respectively, than in the standard NT, whereas corn yields in CC and NT were similar. Despite the use of tillage, soil combustible C and N concentrations were higher at all depth intervals to 30 cm in OR compared with that in all other systems. A uniformity trial was conducted from 2003 to 2005 with corn grown according to the NT system on all plots. Yield of corn grown on plots with a 9-yr history of OR and CV were 18 and 19% higher, respectively, than those with a history of NT whereas there was no difference between corn yield of plots with a history of NT and CC.

Three tests of N availability (corn yield loss in subplots with no N applied in 2003–2005, presidedress soil nitrate test, and corn ear leaf N) all confirmed that there was more N available to corn in OR and CV than in NT. These results suggest that OR can provide greater long-term soil benefits than conventional NT, despite the use of tillage in OR. However, these benefits may not be realized because of difficulty controlling weeds in OR.

No-tillage cropping systems have been shown to offer many benefits to soils and production of grain crops in the eastern USA (Grandy et al., 2006). After 28 yr of continuous tillage treatments in Ohio, the notillage system had higher organic C, cation-exchange capacity, hydraulic conductivity, aggregate diameter, and water-holding capacity than tillage systems (Mahboubi et al., 1993). On well-drained soils, corn and soybean yields were consistently higher with continuous no-tillage than conventional tillage (Dick et al., 1991). No-tillage systems were shown to reduce drought stress and increase yields of grain crops on upland soils in the piedmont of the southern states (Denton and Wagger, 1992). Corn root length density was higher in the top 0.1 m of soil under no-tillage than under conventional tillage, probably a result of higher water-holding capacity, capillary space, and proportion of water-stable aggregates in the surface soil (Ball-Coelho et al., 1998).

Many of the improvements to soils as a result of notillage production are related to increases in soil organic C which in turn relates to improvements in soil aggregation, water-holding capacity, and nutrient cycling (Weil and Magdoff, 2004; Grandy et al., 2006). Soil organic C can also be increased by other strategies, including addition of winter annual cover crops into rotations, diversifying rotations with perennial crops, addition of manure-based amendments, and organic farming, which often employs all of the preceding strategies. For example, soil organic C and N were increased by both reducing tillage and using winter annual cover crops, leading the authors to suggest that the best management system would include no-tillage and a mixture of legume and nonlegume winter annual cover crops (Sainju et al., 2002). Rotations that included at least 3 yr of perennial forage crops had the highest soil quality scores with total organic C being identified as the most sensitive quality indicator (Karlen et al., 2006). Manure- and legumebased organic farming systems from nine long-term experiments across the USA were shown to increase soil organic C and total N compared with conventional systems (Marriott and Wander, 2006). Crop yields and/or soil organic C was increased by organic vs. conventional cropping systems in the East (Pimentel et al., 2005), Midwest (Delate and Cambardella, 2004), and West (Clark et al., 1998).

Most comparisons of soil improvements in organic vs. conventional cropping systems have been conducted under conventional tillage conditions. The dilemma for organic farmers is that the approaches for increasing soil organic C usually require tillage. Specifically, tillage is required for eliminating perennial legumes before rotation to annual crops, for incorporating manure to avoid N volatilization losses, or for preparing a seedbed and controlling weeds. Since an increase in tillage intensity and frequency has been shown to decrease soil C and N (Franzluebbers et al., 1999; Grandy et al., 2006), increases in organic matter by utilization of organic materials in organic farming may be offset by decreases in organic matter from tillage. Some authors have speculated that conventional no-tillage agriculture may provide superior soil improvement and potential environmental benefits compared with organic farming because of the tillage requirement of organic farming (Trewavas, 2004). The need for long-term research has been advocated to assess the relative merits of conventional no-tillage agriculture compared with organic farming (Macilwain, 2004). There is little literature reporting such long-term comparisons. One 6-yr study in Pennsylvania showed that some form of primary tillage was required for crop yields in organic systems to match those in conventional systems, but that a pure no-tillage organic system was not viable (Drinkwater et al., 2000).

A long-term experiment, the Sustainable Agriculture Demonstration Project (SADP), was initiated at Beltsville, MD, to compare selected no-tillage grain cropping systems and a reduced-tillage organic system on a sloping, droughty site typical of the mid-Atlantic piedmont. The standard for comparison was a notillage system typical of that used in this area. Two additional no-tillage systems, one including winter annual cover crops and another including a perennial crownvetch living mulch, were compared with this standard for their potential to improve soil organic matter, reduce external inputs, and enhance environmental protection on erodible soils. Finally, an organic cropping system that reduced tillage to the minimum necessary for incorporation of manure and for weed control was included in this comparison. Performance of these systems during the first 4 yr of the experiment, which included transition years for the organic system, was reported by Teasdale et al. (2000). A simulation of projected yields, economic returns, and environmental impacts was reported by Watkins et al. (2002). This paper reports results from a comparison of these systems over a 9-yr period as well as a 3-yr uniformity trial that followed… <more>

(Source:  John R. Teasdale,* Charles B. Coffman, and Ruth W. Mangum, Agronomy journal-

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100 Years of CLAAS

Today CLAAS, one of the world’s agricultural machinery manufacturer, celebrates its 100 anniversary. On behalf of our IEASSA team I’d like to congratulate this splendid innovative company and to wish them another 100 years of success and ever-burning inspiration to support agriculture business with the new state-of-art solutions all the world!

You can make a small tour through the company’s history by following this link.


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