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Yield maps made simple

Gene Johnston 09/05/2012 @ 2:14pm On the scene at the 2012 Cattle Convention, Nashville

Gregg Carlson has been applying precision technologies to agriculture longer than anyone, perhaps.

“It started for me when I was in the Army Rangers in 1972,” says the South Dakota State University precision farming agronomist. “I first saw how GPS could locate our position, and I remember thinking, ‘How cool is this?’ But I remember also thinking, ‘It will be even cooler for agriculture, to be able to farm by precise location.’ ”

Carlson went on to become an agronomist, and his chief area of interest since has been application of precision techniques to improve farm performance and economics. It's been a long journey, and finally there are some payoffs.

“I call myself a ‘why's guy’, I always ask, ‘Why?’ Why does one part of a field consistently yield more? We have all this data, how can we turn it into usable information? There are lots of unknown returns to yield maps, and the known returns are small. But I think we can improve them,” Carlson says.

50×50 Grids

For the serious yield mapper, it's worth your time to manage the data you have accumulated, he continues. And it doesn't have to be complicated.

“I start with the two things I most want to know: What is the average yield in a field or zone in a field? What is the variation of that field over time?”

Carlson prefers to look at data in 50×50-foot grids, giving about 3,000 data points per 160-acre field per year.

“You can't really manage plots any smaller than 50×50, and that many data points is a workable number for even a slow computer,” Carlson says.

With the yield data in hand, Carlson puts fields into three categories:

1. The consistently high yield areas.

2. The consistently low yield areas.

3. The consistently inconsistent areas.

“Then I treat them differently,” he says. “And I always associate a specific year data with that year's precipitation data. The precipitation information often explains a lot of yield patterns year to year.”

1. Consistently high

These are your best fields and areas of fields, always at the high end of yields, and where you want to ensure that inputs do not limit yield potential. Give them fertilizer, seed population rates, and racehorse hybrids that will maximize yields.

“You don't want to limit the yield potential in these areas of the field,” Carlson says.

These areas are also the fields where you are mining plant nutrients the hardest, he says. “You're taking lots of nutrients off of them at harvest, and as a result, they are often your lowest soil test fields for phosphorus and potassium. Give them all they need; you want to push these areas. They're the areas where someday we're going to grow 300-bushel corn, 100-bushel soybeans, and 150-bushel wheat.”

2. Consistently low

When your yield maps show you these zones, it is a good time to ask why. “Is it drainage? Soil pH? Hard pan? Weeds? As an agronomist, you need to know what's going on in these areas, why they are consistently low yielding, and develop a plan to improve them,” says Carlson.

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It couldn't have been 1972 12/10/2013 @ 9:57pm The first GPS satellite wasn't even launched until 1978!

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