Geo-referencing Soil pH for Liming
By Jerry W. Engler
New technologies lead to more changes plus keep the environment cleaner.
Jeff Mayfield at Ag Service near Hillsboro, Kansas, finds that often times, when the company begins a new farm technology, more new and better ways of doing other things come up.
“It just keeps snowballing.”
That’s the way it is with the satellite geo-referencing and computer precision the company is using for liming area farm fields. Mayfield said it appears the practice will lead to possibly more precise applications according to point of need for seed, fertilizer, and maybe even pesticides.
It already makes those other practices do better where applied by pinpoint correction of soil acid/base balance.
The company can already hand a card developed from the liming computer program to a farmer who used the technology to plug into the GPS computers on his newer tractor or planter to regulate changing rates of seeding.
For example, Mayfield said, if the farmer is planting corn, he may want to put less seed on clay tight soils in upland parts of the field that grows corn poorly, but more seed in a part of the field with rich loamy soil that grows corn well.
To understand all of this, it probably helps to know something of the method of the liming, and how it helps. Even though Ag Service has had the current liming service for three years, Mayfield said it probably is still unique in this area.
Now Mayfield isn’t saying a producer should entirely throw out the way things have been done in the past, he said. The old method of going across a field on a four-wheeler or walking to take soil core samples, then mixing them to send in for testing to determine average pH across the field before liming still has value, he said.
But the new method delivers precision with “extremely” greater productivity, he said.
It may not cost less to lime because delivery is balanced out in putting more lime in spots where it is needed, and less lime in spots where it is not needed. But the price difference is created in higher crop yields and better use of other chemicals that need the proper pH balance to perform correctly.
The process performs so well, Mayfield said, that farmers often find the phosphorus they have applied for years slowly becomes available to boost crops. It also may mean that less phosphorus is washed off, he said, which often is a concern to environmentalists.
The pH number is a logarithmic value related to the balance of hydrogen and hydroxide (acid—base balance). A pH of 7.0 is about neutral while numbers lower are acidic and numbers higher are basic.
According to Ag Service data, pH over several thousand acres in this area has varied from 5.0 to 7.5 with an overall average of 6.2. In many cases the areas of fields with lower pH “acidic” soils “are the better quality soils with historically higher yield potential, but are now dramatically underperforming.”
To put the need for soil correction or liming in order of crop need, Mayfield said the number one crop that needs liming the most is alfalfa. “Alfalfa wants pH right at 7.0. It hates a lower pH.
“Then number two comes soybeans, then corn—and milo about the same—and then wheat. Wheat has been more tolerant of conditions for us. We have wheat fields down around 5.0 that still produce.”
Mayfield said Ag Service starts its liming service with a high density geo-referenced soil survey test machine pulled behind a tractor at four miles an hour.
The device has paired coulters in the ground, and sends an electrical current between them.
Mayfield said this determines the heaviness of the soil. Less lime may be required on the more sandy soil and more on the clay soil, both within the same field and typical of this area, he said.
In the same operation, a shoe, or little shovel, scoops up cores of soil to go against a little glass-eyed sensor to determine pH.
Mayfield said the GPS system at the same time is laying out elevation with such precision that it could be used later for the construction of terraces, waterways and drainages. A computer generated map from the operation would show land contours, and it also produces colored map pinpointing lime needs.
In the next phase of the Ag Service operation, a lime-gator variable rate applicator machine uses the computer card produced to apply a slurry of 92 percent lime solution applied at 50 percent mix with 50 percent water, Mayfield said.
The lime-gator puts the lime, a calcium mix that brings pH up, precisely where it is needed in the field to bring 5.0 pH readings on that good soil up to the upper 6.0’s. And, Mayfield pointed out, it doesn’t apply it where it isn’t needed, therefore not being counterproductive by making some soils too high in pH.
This gets away from the old application of lime which lacked precision in putting the substance on dry and evenly across a field with part of it blowing away in the wind, he said.
The process is a real “gateway to variable rate application” for fertilizers, seed, pesticides or other chemicals, Mayfield said.
Already, the program can be plugged into the field monitor of a combine at harvest with four or five years worth of information to greatly increase the data available to a producer, he said.
For farmers, it means significantly increased dollars in productivity plus environmental savings.
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