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You Are Here Sunflower Magazine > Site-Specific Entry Generates Plenty of Data... & Questions


Sunflower Magazine

Site-Specific Entry Generates Plenty of Data... & Questions
March 1998

Kent and Cindy Stones learned a great deal during their first three years of experimentation with GPS-based site-specific farming technology. But perhaps one of their biggest lessons has been how often this technology can end up generating more questions than answers — particularly during its initial years of use.

Still, this north central Kansas husband and wife team is sold on the value of pre-cision farming technology and techniques. And, they’re looking forward to both the near- and long-term dividends which they are confident will accrue from its being utilized in their farming operation.

Like many producers, Kent Stones has discovered that the value of GPS-based technology is inextricably intertwined with the twin pillars of (1) the accumulation of as much accurate data as possible, and (2) the proper interpretation and management of those data. Shortcomings in either area, he points out, reduce the value of site-specific agriculture for the producer.

“My expectations were far higher than what we’ve been able to accomplish thus far,” Stones admits. “After three years, we’re still struggling with just the basic data accumulation and processing. The industry is new enough that there are continuous changes; and for every two steps forward, it sometimes seems we take one backward.”

More specifically, Stones is still wrestling with how to employ variable-rate inputs — fertility, seeding, herbicides — based on his data acquisition to-date.

“We’ve done some grid soil sampling,” he reports, “and can generate maps of our fertility levels. But for me, it has raised more questions than it has provided answers.” Part of the problem revolves around the topographical variability in some of his fields: a combination of small fields, terraced ground, hillsides and level areas. “If the grid point is directly on top of a terrace line, will that be representative of the 2.5-acre grid? Probably not,” Stones illustrates. “Or if your grid point is not in a terrace, yet there’s a terrace going through the 2.5-acre grid, is your sample going to be representative? Not completely, because it hasn’t accounted for that manmade terrace line.”

The ironic twist is that “variable” fields are exactly the ones which should benefit most from the application of site-specific technology, Stones points out. So his goal is to find ways of overcoming such obstacles, generate more-accurate data — and then put those data to work.

“One area I see as being more important to me than what we’re currently doing is to be able to monitor fertility on-the-go and then apply fertilizers accordingly,” he observes. “To have a complete analysis every two seconds of existing nitrogen, phosphate, potassium, pH — and then have the ability to come back in and apply tailored blends at two-second intervals. Maybe that’s the way we’ll go in the future” as opposed to 2.5-acre grids.

Stones expects his first venture into variable-rate application to actually come with herbicides. “It’s going to be tied to soil type,” he projects. “Soil type and organic matter are closely related, and herbicide effectiveness is closely tied to organic matter.” The opportunity lies in the ability to vary herbicide rates on-the-go, based on soil type, to maximize efficacy without over-applying.

“For instance, in a very low-organic area of the field, a lighter rate of herbicide will achieve excellent weed control,” Stones illustrates. “And in a high-organic area, it should take a higher quantity of herbicide to achieve the same level of weed control. If we know our soil types, we can change herbicide rates as we go.

“There may be a time when we have a sprayer [carrying] multiple herbicides, and we can ‘pick and choose’ as we go,” Stones continues. “But that’s a ways down the road for us.”

For 1998, Stones is installing a GPS receiver and Raven controller on his Melroe SpraCoupe, “so we intend to do some variable spray applications this spring,” he indicates.

Variable-rate seeding — taking into account soil type, terrain and moisture conditions — is another area where the Smith County producer envisions a very beneficial fit for his operation, utilizing variable-rate drives being developed for air drills. That technology will couple with the yield data he gathers with the AFS equipment and yield map software he runs on his Case combine. Variable-rate seeding “is a tailor-made situation for us, and we’re really looking forward to it,” Stones affirms.



Stones has been running his combine yield monitor and generating yield and moisture maps since 1995. He says these data have been one area where he’s had to adjust expectations and practice patience. His yield data have been very accurate — when checked against weigh wagon results — on a field-wide basis. However, he has not been satisfied with the accuracy for specific locations within fields.

Row length seems to lie at the heart of the matter, according to Stones. “I’ve consistently observed that in a long row of high-yielding crop, the longer I stay in the row, keeping the combine full, the yields continue to climb up to a certain level. But it may take three-eighths mile before the yields stop climbing on the monitor.” If he’s harvesting a field where the longest row is one-fourth mile, “I never reach that ‘magic’ three-eighths mile,” Stones explains. “So if calibrated for long rows, field accuracy is not going to be as good.”

Despite his current misgivings about the accuracy of his site-specific yield data, Stones believes the information is still useful “if I’m identifying trends.”

An example was a 1996 sprinkler-irrigated corn field. Stones’ yield maps indicated a strip that ran 44 bushels higher than the surrounding field portions. Because the strip was so clearly defined and consistent, he knew the difference had to be due to human influence, not the soil type or terrain. Stones later realized that lime trials had been conducted on this field several years before, and that particular strip had received two tons of lime per acre. “Based primarily on that information, 1,600 acres were limed in 1997,” he notes. The result? A 40-bushel difference in corn yields versus non-limed areas.



Though not yet reaping many of the hoped-for dividends of his site-specific farming investment of time and money, Kent Stones is confident this is the direction his farming operation should — and will — continue to move.

“Maybe it’s not yet doing what I originally expected, per se; but it is causing me to be more information-oriented in my operation,” he says. “I cannot look at a field anymore and think of it as a blanket: one uniform seeding rate, fertilizer applica-tion or herbicide treatment. Whenever I look at a field, I automatically begin to think in terms of precision application.

“It brings me closer to my operation. I’m much more aware of what’s going on.” — Don Lilleboe

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