The Value of a Yield Map

Anna Dugas, Barbosa, Roberto N., Frazier Jr, Ralph L.

An EC map like this one can help the farmer identify differences in soil structure.

A grid sample map can ensure all soil zones have equal sampling representation.

A yield map.

A yield monitor is the first step many producers take into precision agriculture (PA). A yield monitor alone provides limited information whereas when combined with Global Positioning System (GPS) receivers, yield-mapping software and proper training, it becomes a useful management tool. The goal for properly interpreting yield data is to provide answers to the question that plagues most producers -- “How can I increase profits on this field?” Producers have to remember that a yield map is not the magic bullet that will solve all their problems. Colorful maps are not knowledge. If yield maps are to be any of any real value, the data generated from them must be incorporated into the decision-making analysis and overall planning process of the farm operation.

Many times a yield map raises more questions than it answers and becomes a potential source of frustration. A yield map only documents crop yield, not what caused the yield difference. As yield maps are evaluated, variability can be grouped into two categories: (1) producer management practices, (2) naturally occurring or environmental effects.

Producer management practices:

  • Field History -- tillage practices, previous crops, spills, utility lines, construction
  • Compaction -- working wet soil, heavy traffic, drainage
  • Water management -- applying irrigation uniformly, improper drainage
  • Equipment/mechanical errors – dependable GPS signal, proper calibration of equipment

Naturally occurring variables:

  • Weather – flood/drought, heat/cold
  • Soil fertility – pH, soil nutrition, deficiencies, organic matter content
  • Soil physical properties – soil type, field variability
  • Pest concentration – weeds, insects, diseases

After studying a yield map, try to categorize yield differences into one of these two groups. Producer management practices are easier to identify and correct, if economically feasible. Naturally occurring variables are more complex, harder to identify and more difficult to correct. Suggestions for identifying soil-related issues would be to use electrical conductivity measurements (Eca) to identify differences in soil structure.

This information then could be used to set up a grid or zone sample to look for fertility and pH problems in the field. Once problem areas are identified, use a variable-rate application to apply what may be needed and only where needed. Another area to look for would be water management. Can I add a drainage ditch to move the water off the field in a timely manner, or alter the slope of the field to be able to get water to an additional part of the field?

Don’t be quick to jump to a conclusion. Seek input from knowledgeable individuals about fertility, drainage and irrigation before making changes in your operation. The producer’s goal should be for yield that produces maximum return for dollars invested.

12/1/2009 2:51:13 AM
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