Weld Mapping Could Improve Crop and Resource Management

Chapter 10 – Economics and Application, No. 7, Spring 1990

Roger Veseth

Much of the Northwest cropland contains fields with variable landscapes and soils. Consequently, production potentials or limitations and management concerns can vary across a field.

Whole-field management strategies typically do not make the most efficient use of production inputs nor provide adequate protection of soil and water resources. For example, when using an “average” nitrogen (N) fertilizer application rate across a field with variable yield potentials, low-yielding portions of a field may be over-fertilized while high-yielding portions maybe under-fertilized. This can result in lower overall production efficiency and profitability.

Over-application of nitrogen fertilizer for the yield potential can also result in excessive protein levels in soft white wheat (an increasing marketing problem) and increase the incidence of some wheat diseases, such as dryland foot rot (Fusarium) and strawbreaker foot rot (Pseudocercosporella). It may contribute to surface or groundwater contamination as well. Increased public pressure is being put on producers to implement management practices which more effectively protect soil and water resources.

One part of fine-tuning field management for increased production efficiency and resource protection is adjusting production inputs and practices to variations in yield potentials and limitations in each field. An important component in identifying management units within a field is to accurately document yield variations at harvest.

Research Initiated

Development of equipment and technology to determine yield “on-the-go” with a combine, and to record yield in relation to field location has been the focus of a research effort by Charles Peterson, University of Idaho agricultural engineer. The project is being conducted with fellow agricultural engineer Edwin Dowding and research technician John Whitcraft, and is in cooperation with Kyle Hawley, a Moscow area farmer.

Since yield mapping technology would be useful in addressing several production and environmental concerns, supplemental funding for the project has come from several sources. These include: STEEP (Solutions To Environmental and Economic Problems), a cooperative research program on conservation farming technology in Idaho, Oregon and Washington; LISA (Low-Input Sustainable Agriculture), a USDA program which provides funding for research and educational projects on the topic; and the Idaho Wheat Commission, which allocates research grants from Idaho producer’s wheat check-off funds.

Value of Yield Determinations

Having the capability to determine yield throughout each field at harvest from a combine would provide several management opportunities. Once producers were able to more accurately determine differences in yield potential in contrasting areas of the field, they could begin to develop differing management practices. In hilly cropland, for example, if yield monitoring determined that wheat yields on the bottomland, sideslopes and ridgetops averaged 90, 60 and 30 bu/acre, respectively, producers could begin to delineate fertilizer management units for the appropriate yield potentials in the field. Management units could then be soil tested separately for determining fertilizer requirements. Differences in soil water content could also be used to refine yield potentials.

An increasing number of commercial fertilizer applicators now have the capability for limited “on-the-go” adjustment in application rates. This will be the trend in fertilizer application equipment for the future – driven by the demand for increased production efficiency as well as the increased emphasis on water quality protection. Technology for computer-controlled fertilizer applications, based on computerized field maps of soil test results, is already being used commercially for dry fertilizer application on a limited basis by Cenex/LandO-Lakes. Developing computerized yield maps would compliment these systems by permitting adjustments in fertilizer applications to fit variations in yield potential within the fields, as well as soil nutrient levels.

Field areas specifically monitored for yields could also be those used for comparing different management treatments in on-farm research efforts. Many farmers are evaluating new management options each year, such as fertilizer types or rates, crop rotations, crop varieties or tillage practices. Having the capability of direct yield comparisons from the combine at harvest could help improve the speed and accuracy of these evaluations, and promote more on-farm testing.

With a field navigation system to identify combine location in a field, other management uses are possible, in addition to developing a yield map. The researchers point out the option of having a coding system for identifying problem areas in the field, One example would be enabling the combine operator to pinpoint areas of perennial weeds on a field map to allow accurate spot application of herbicides after harvest or during the next crop.

Equipment for Combine Yield Mapping

The goal of the University of Idaho project is to develop equipment and procedures for instantaneous display of yield in the combine cab in a form that can be observed by the operator, and can be stored in a computer for development of a field map. The complete yield mapping system would include an on-the-go grain monitor for the combine, combine speed sensor, field navigation system, and a portable data-gathering computer with specialized software.

Although the complete system will take some time to perfect, certain components of the system could be available to producers in the near future. For example, even without the field navigation system, producers could monitor yields in areas of fields that are visibly identifiable based on topography, soil color, aspect (north vs. south slopes) or other characteristics. They could then delineate their own management units to best fit their field and production system. This technology could enhance the production efficiency of divided-slope and contour strip farming systems for soil erosion reduction in sloping cropland.’

Grain Yield Monitor

After evaluating many different approaches to monitoring the amount of grain harvested, the researchers developed a grain monitor which consists of a permanent magnet motor driving the clean grain auger. For test purposes, they utilized an IH model 453 combine. The clean grain auger on this model is driven by the clean grain elevator drag chain. To adapt the new motor drive, the drive sprocket was removed from the auger shaft and a bearing installed to separate the elevator power from the clean grain auger drive. Laboratory and field calibration data for the yield monitor have demonstrated a high correlation between monitored motor amperage and grain flow rate. Grain yield was also accurately predicted after field calibration which incorporates combine speed and header width.

Speed Sensor

The speed sensor was the easiest component to install because many commercial speed sensors are available. A John Deere sensor was selected because the researchers had used it in previous experiments and were familiar with the output signal to be recorded in the computer. The sensor is a sonar-type with an output pulse frequency proportional to ground speed.

Field Navigation

To develop an accurate yield map of the field, a field navigation system is needed to determine exact coordinates of the combine in the field. Hilly topography of the Palouse and other Northwest cropland areas limits the use of line-of-sight field navigation systems which are currently available. The LORAN (Long Range Navigation) system, used by marine and aircraft industries, was tested in 1988 but it did not provide acceptable accuracy.

A new satellite navigation system called Global Positioning System (GPS) was initially tested by the researchers in 1989. Latitude and longitude are determined from a time-based signal transmitted from satellites orbiting the earth. When fully operational, the GPS will consist of 21 satellites. Approximately 11 are now in orbit. Using the partially operational GPS system, accuracy was within about 100 feet. Use of a land-based stationary unit for error correction can possibly increase the accuracy to within about 3 feet. A land-based unit could cover a radius of 75 to 250 miles. Further research with GPS is planned this year.

Data-gathering Computer

A data-gathering computer is being fabricated from commercially-available components. It will store data from the grain yield monitor, speed sensor and GPS. Development of software for providing usable information from data collected on the combine is now in progress.

Future Plans

The researchers will continue testing GPS as a combine field navigation system in 1990 as more of the system becomes available. Field calibration and development of the combine yield monitoring system will also be continued, as well as the data-gathering computer and software. The UI researchers hope that a complete combine yield-mapping system maybe available within the next 5 years if adequate funding is provided and research progresses as planned. Technology and equipment for combine yield monitoring in identifiable units of a field, without sophisticated field navigation and computer mapping components, should be available in the near future.

Use of Trade Names

To simplify the information, trade names have been used. Neither endorsement of named products is intended nor criticism implied of similar products not mentioned.