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Learn the Most from Yield MapsAgroConnect
Farmers share findings of new technology

By Larry Reichenberger
Successful Farming
December 2003

Brian Jenson, Stephan, MN Farmer

Brian Jensen is among the many farmers trying to learn more from the yield maps they’ve collected.

Combine yield monitors have lead the rush to precision agriculture. However, in their wake this new technology has left many farmers knee deep in yield maps that are too valuable to ignore yet too complicated to understand.

This is the challenge that lead Stephen, Minnesota, farmer Brian Jensen to seek advice from other farmers. Last summer, he posted the question shown above on Successful Farming’s Agriculture Online internet site. We’ve gathered some of the responses, along with input from other farmers and industry experts, to help provide him an answer. 

Jensen explains that he uses a Ag Leader PF3000 yield monitor in his combine. To view yield maps, and perform basic management of the data, he has relied on the SMS Basic (Spatial Management System) software that came with the monitor. Brian Jenson's Quote

Like most farmers, Jensen was quick to spot drainage problems on his first yield maps “It was obvious and we did some ditching and laser leveling to correct the problem,” he says.

With his appetite whetted by initial success, Jensen is now anxious to get even more from his yield maps.  “We’re collecting a huge amount of data and are anxious to perform some additional analysis on it. We want to know what other farmers are learning from their yield maps and how they’re using the information,” says Jensen.” 

Des Moines, Iowa, based consultant Dave Chaffin, with Agronomic Solutions, Inc., responded to Jensen’s online question. “There are a lot of farmers in this same situation with notebooks growing fat with yield maps,” says Chaffin. “The precision ag industry is just beginning to deliver ways for farmers to handle all the information they’re collecting.”

Chaffin explains that most combine yield monitors come with basic software that allows users to display yield maps and do simple analysis. “Taking the next step to perform indepth analysis requires more powerful software that contains a GIS (geographic information system),” he says.

GIS software stores, displays and analyzes yield monitor data and can identify relationships between yield data and other layers of information.  “We use SSToolbox software for this GIS capability,” says Chaffin. ‘It allows layers of data including yield maps, soil types, soil test results and other information to be compared for individual areas of a field.”

The complexity of GIS software, and the computer power needed to run it, can pose a challenge to many farmers.  “Some are certainly capable, but consulting companies provide an alternative,” says Chaffin. “We charge from $.50 to $1 per acre depending on the amount of information and degree of analysis required. Our speciality is using soil type and yield map information to design management zones and direct soil sampling. We charge $5.50 per acre for this service.” 

Normalize yield maps.

Gary Wagner, Crookston, MN Farmer

Gary Wagner turns multiple years of yield maps into yield stability maps to focus his attention on factors that he can and can’t control.

Ted Macy, president of MapShots Inc, Cumming Georgia, says GIS software programs, which cost from $1,500 to $4,000, allow farmers to analyze multiple years of yield map data. “Three years of yield maps are probably the minimal amount required. By normalizing (combining) this data, a true picture of yield variability emerges. From that picture, management zones can be developed in the field,” he says. 

A decade of yield map data is more a blessing than a burden for Crookston, Minnesota farmer Gary Wagner. “The more years of yield maps we have means our information becomes more accurate. However, it also means we’ve had to find a way to organize and present this information,” says Wagner.

Using MapCalc software to prepare data and the GIS capability in S S Toolbox software to analyze it, Wagner has normalized yield maps from multiple years to develop single ‘yield stability’ maps for each field.

Wagner, who farms with his brothers Wayne and Daryl, says these yield stability maps, like the one shown here, make it easier to identify and manage production problems.  “Scientists have identified more than 40 factors that influence crop yield variability. We can’t possibly analyze for all of those, and more than half of them are environmental factors that are out of our control anyway. Maps showing yield stability focus our attention on problem areas of the field more likely to provide a pay off.” 

The example is a 108-acre field divided into 100-square foot cells.  Four years of yield maps, made during wheat harvest, were combined to find the maximum yield achieved in each grid as well as the year to year stability of those yields.

“Dark green cells on the map have the highest maximum yields and the greatest consistency,” says Wagner. ‘Obviously, we’re doing the right things in those areas so there’s no reason for change. On the other hand, if an area is consistently low then we need to try to figure out why. If the limitation is because of soil type or some other factor that we can’t do anything about, then there’s no need to apply much fertilizer to that area.” 

Wagner explains that grids of the same color are grouped together into management zones for soil testing, but fertilizer is applied to individual cells.  “A single dark green cell wouldn’t be soil sampled separately, because of the cost, but it would get the fertilizer rate that correlates to it’s high yielding color,” he explains.

Jim Kinsella

Jim Kinsella says yield maps are great, but still no substitute for actually being on the combine.

For more information about yield mapping and other agronomic topics,
visit Agro-Connect online at
Sponsored by Dow AgroSciences.

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