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Messages from yield maps
New technology pays by highlighting production problems

Successful Farming
Written By:  Larry Reichenberger
November 1997
see this issue’s table of contents and stories >>

Gary and Daryl Wagner
Yield mapping has helped Gary (left), Wayne, and Daryl (right) Wagner
uncover production problems on their farm.

Farmers hoping to use yield maps to guide them on a road to increased profitability can take heart from the Wagner brothers.

After fours years of reading those maps from their Crookston, Minnesota, farm, Gary, Wayne and Daryl Wagner have found that the maps can indeed lead to greater profits and point the way to increased production, reduced costs, and improved environmental safety along the way.

“Yield monitoring and mapping techniques have helped identify more than 40 factors that affect yields on our farm.  Roughly half of those are environmental conditions that we can’t do anything about, but there are enough factors we can manage to more than pay for the technology,” says Gary.

The Wagners list a dozen of these “manageable” factors that repeatedly occur.  The list includes drainage, variety selection, insect/weed control, crop rotation, tillage, compaction, soil pH, herbicide, seedbed conditions, fertilizer placement, and fertility.

“It’s no accident that drainage is first on this list and that fertility is last,” says Gary.  “We’ve found a strong relationship between drainage problems and lower yields. Consequently, we’re paying a lot more attention to keeping drainage ditches clean.

“On the other hand, we’ve not seen much correlation between yield levels and fertility variations.  This isn’t to say that fertility doesn’t mater, but that is is being overpowered by some other factors on our farm,” he adds.

A closer look

The yield map shows losses due to poor drainage in one of the field. Each spring from 1993 to 1996, the Wagners located wet areas in this field using mapping software and a Global Positioning System (GPS).

“We carried the mapping system on an ATV and simply drove around the wet areas.  Four years of the resulting maps were “normalized’ to show consistently wet areas,” says Wayne.

“The yield map for 1995 shows that sunflower production declined by more than 1,000 pounds per acre in these wet areas.  In sugar beets, these poorly drained areas present even more of a problem because of timeliness concerns,” says Gary.

The same yield map shows the value of proper variety selection.  The low yielding variety area on the ride side of the field was planted to a different variety. Yield suffered by 1,200 pounds per acre. “Our sunflowers sold for an average of 20 cents per pound that year, so that variety produced $240 per acre less income than the other,” says Gary.

Learning by doing

The Wagners collect harvest data at two-second intervals with an Ag-Leader yield monitor. This gives yield information on 20x28-foot blocks of their fields. They have worked with both six- and 12-channel GPS receivers and obtain differential correction signals from a tower 15 miles away.  Accuracy has been 10 feet or lass.  Last season they also equipped their sugar beet harvester with a Harvest Master yield mapping system.

On of the first lessons the Wagners learned from heir yield mapping efforts dealt with soil compaction. The map below shows a wheat field from their 1993 season.

AWG Farms Tillage Map
AWG Farms Crop Rotation Map

Yield losses shown in the upper left corner of the map at left resulted from tillage when the soil was wet.  Operations a day later on the rest of the field boosted yields 20 bushels/acre.  Crop rotation increased yields on the field at lower left.  Wheat on the left side was rotated with sunflowers, while the right side was continuous.

AWG Farms Drainage/Variety Map

“When we looked at this map, we immediately noticed that one corner of this field yielded less 0 the what there was making 20 to 30 bushels per acre, while the rest of the field was making 50 bushels an acre. We worked this field diagonal before planting, and we stopped right at that point because we thought it was too wet.  Soil compatction and poor seedbed conditions cause those yield declines.  Now we don’t make that mistake,” says Daryl.

Another management practice proven sound by the Wagners’ yield mapping has been crop rotation. The yield map below highlights their findings.

“Head scab has been a serious problem in wheat in recent years,” says Gary. “Yield mapping proved to us that crop rotation could help combat this disease.  One portion of this field was wheat on wheat, while the other portion was wheat grown after sunflowers.  The portion of the file that had been rotated yielded 10 to 15 bushels per acre more.”

Weed Control

Yield maps are also helping to sharpen the Wagners’ weed control program.  For example, while harvesting wheat hey use a field marking feature on their yield monitor to map areas infested with wild oats.  When fields are again rotated to what, they use this information to vary chemical rates to match the weed patterns, or even spot spray to match weed pressure.

“On one 160-acre field, we found only about 50 acres contained enough wild oats to justify a full chemical treatment. The result was savings more than $400 compared with applying a full chemical rate to the entire field,” says Gary.

The  Wagners have little doubt that when taken together, all the benefits they’ve found to yield mapping will more than pay for the technology.  They have roughly $10,00 invested in their yield monitor, mapping software, computer, and GPS equipment.

“The combined benefits from solving the various problems that yield mapping is pointing out to us will pay for the equipment in a single year. However, that payoff doesn’t start until you have several years of data on hand to make decisions.  Year-to-year variation is considerable,” says Gary.

“And farmers must learn to use computers and to read and understand these maps themselves to get the full value of the information they gather.”

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