Precision Maps Can Reveal What Happened After the Fact

Maybe Hybrid A beat Hybrid B because it had an advantage.

Published on: Oct 27, 2008

Those that still don't see the value of yield maps, and there are some, haven't encountered a situation where they scratch their head, trying to explain what happened after corn is weighed across the scales. The only records left at that point, besides dead, flat corn stalks, are whatever data you've recorded in various precision maps. Here's a real case where a series of maps helped explain a discrepancy, and made more sense out of what the farmer saw

A farmer split a 40-acre field of good, rich, black soil, well-drained by a tile system, into two. On one half he planted hybrid A, and on the other half he planted hybrid B. Hybrid A was from company X, and hybrid B was from Company Y. The farmer has dealt with both for some time, and likes certain products of each company on various soils. His farm consists of multiple soil types spread over multiple locations.

In this particular field, soil fertility is high and he planted a healthy population, going for high yield. When the combine passed through the field, hybrid A averaged at least 20 bushels more per acre than hybrid B. The salesman for company X was pretty excited, smiling all the way to his pickup. After all, it wasn't a replicated test, but the soil type in the field was fairly uniform. Even the farmer acknowledged that was the case.

But later the farmer began pulling up other layers of data he had recorded during the season on his computerized field monitoring GPS system. First, it occurred to him that this was the last field tilled in the fall. Then he remembered getting rained out. Sure enough, he had a layer that recorded tillage passes. The side where hybrid A was planted was tilled but the half where hybrid B was planted didn't get worked until spring, almost to the row.

Then he thought some more and pulled up another layer of data. When he tilled last fall, he also deep-applied P and K fertilizer. Application rates showed on his maps. But after he got rained out at the close of the season, the half of the field where hybrid B was planted didn't get P and K until this spring. It was spread on top. Hmm..could that make a difference?

There was still one more missing link- nitrogen. As he thought about it, he recalled applying anhydrous ammonia on the entire field the fall before he planted. Then, fearing that N may have been lost due to the wet spring, he decided to apply another shot at sidedressing time last summer. But he couldn't remember if he sidedressed the whole field or not. It stuck in his mind that perhaps he ran out, and with N being high anyway and the crop looking OK, decided not to finish the last half. Sure enough, when he pulled up his N application maps, that's what happened. And you guessed it- he applied extra N on the half of the field where hybrid A was planted, not where hybrid B was planted.

Is all that proof that hybrid B would have equaled hybrid A given equal treatment. No, but it is enough for the farmer to keep hybrid B in the line-up another year. And if this case was before a jury, it would surely be enough evidence to create 'reasonable doubt' as to whether hybrid A truly out performed hybrid B, or whether it took advantage of yield-boosting opportunities that hybrid B didn't get.