Tennessee farmer testing variable-rate applications in cotton

Ed Karcher doesn't hesitate when asked why he is going to variable-rate applications of inputs on his farm. “It will save me money,” he said.

Karcher, who farms with his brother, Tom, near Somerville, Tenn., was introduced to precision agriculture by his consultant, Tim Sharp, a professor at Jackson (Tenn.) State Community College.

At the time, Sharp asked the Karchers to be cooperators for JSCC's precision agriculture program, which involved boundary mapping and grid sampling using the global positioning system.

In March, Sharp held a precision agriculture seminar which Karcher and 30 other west Tennessee farmers attended. Speakers included Sharp and John Freeman, who has been working with Mississippi producer Kenneth Hood's precision agriculture project.

The speakers convinced the Karchers that precision agriculture could help them cut costs and bump yields in their cotton production program. “We showed them,” Sharp said. “The general consensus among the farmers was ‘Yes, this is what I'm going to have to do. Now, how do I do it?’”

According the Sharp, three recent developments have turned variable-rate application into a practical practice: “The digital cameras available to take the kinds of images we need; the software that will allow us to analyze images to create this data layer; and computers with enough processing power to process the data.”

Variable-rate technology will focus on NDVL images (normalized differential vegetation index), generated from the digital camera (shot from an airplane).

For some growers in the variable-rate program, that imagery is already being done, but the bulk of the photography will come in early August, according to Sharp. “They're shooting for 500 to 700 heat units after five nodes above white flower.”

A software program called SS Toolbox will convert the image to a plant vigor map, which has a very close correlation to a final yield map.

This is used to help write a prescription, or mission plan, for the variable rate application of inputs the following year. The idea is to vary inputs according to yield expectation — inputs are reduced in lower-yielding areas of the field and raised in higher-yielding areas. Sharp says that yield variations can range from 350 pounds to 1,500 pounds in a cotton field.

Farmers will be responsible for purchasing GPS technology, yield monitoring, grid sampling and performing the variable rate tasks. “They need to contract out all GIS analysis projects, GIS mission planning and all activity using imagery,” he said. “You have to have a basic level of training for the grower and his personnel. And continuing education to teach the basic skills.”

In most cases, a farmer can modify existing equipment for variable-rate applications. “If you have a High Boy, you have a controller. You just add the plug-ins that go with it. If you have a planter, you have a variable rate planter. You have to add the controller to it. If you're putting down liquid fertilizer with a coulter rig, you have a variable rate nitrogen applicator.

“Those aren't a lot of big ticket items. If you get a yield monitor, modify your planters, sprayers, I think you'll be hard-pressed to spend $15,000. And that should cash flow in the first pass.”

As for cost savings, Sharp added, “You know before you crank up exactly what the cost savings are going to be.”

Computer imagery from several fields indicate that properly applied fertilizer can save as much as $75 an acre. “Growers are spending as much as $50 more than they need in expenses, which could be corrected through variable rate applications.

Karcher is preparing to do some variable-rate applications this coming season. “Kenneth Hood bought a variable-rate truck this year and will be applying variable-rate fertilizer for us,” said Karcher, who has already grid sampled his farm. “He said he saved over $100 an acre by going to variable-rate inputs.”

The Karchers are also setting up their High Boy for variable-rate applications and their cotton picker will be equipped with a yield monitor this fall. “We won't have time to get set up for variable-rate planting this year with cotton planting so close, but we should be able to vary our Pix rate this year.”

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