Variable-rate aerial application of dry fertilizer is a new “prescription” that gets nutrients in the soil quickly and efficiently, even when wet, muddy fields keep ground rigs parked.

Satellite imagery for aerial chemical applications is still high-tech for most growers. But those who use it know that liquid applications of herbicide, pesticide and fertilizer are effective.

However, aerial dry fertilizer can cost less than liquid applications, and costs are comparable to those for ground rig apps of dry materials, says Mark Kimmel, an Itta Bena, MS, grower and aerial applicator.

He believes in the new fertilizer program because it works on his 1,500 soybean acres, 500 corn acres and 1,000 in cotton. And since his Mississippi Delta flying service is equipped with variable-rate dry fertilizer applications, he's been on top of the technology from day one.

“In the Delta, it's often too wet to get into fields when applications are needed,” says Kimmel.

Filip To, a Mississippi State University (MSU) agricultural engineer, says the advances in variable-rate application (VRA) technology are helping growers do timely and precise applications cost effectively.

Aerial VRA involves taking satellite or airplane photo images of a field. Images are then analyzed with ground-truth to determine which areas of the field require chemical applications and at what rate.

That VRA “prescription” is then loaded onto a data card that is read by a computer in the spray plane cockpit, and chemicals are then automatically applied at the prescribed rates site specifically.

Dry fertilizer applications add a new dimension. “You can make precision applications of potash, potassium (K) and urea at about the same cost as using a ground rig,” says Kimmel. He estimates that for a typical 150-lb. application of dry nutrients to a corn crop, the cost is about $7/acre, plus the fertilizer cost.

WITH THE ABILITY to hold costs down, Kimmel aims to convert his entire farm to dry fertilizer if possible, anticipating that two-thirds of his acres and nearly all of his corn will be ready for the dry applications in 2009. “I saved close to $15,000 by using the dry application on only one-third of my farm the first year I used it in 2007,” he says.

He flies an Air Tractor 502 plane, a staple among many aerial applicators. It is equipped to hold 500 gal. of liquid chemicals, and 4,000 lbs. potash, 3,200 lbs. urea or about 3,800 lbs. K.

He uses an Accu-Rate VRA system from Air Repair Service of Cleveland, MS, which was developed in collaboration from MSU's To. He helped develop the sensor and program that measures the flow of dry material through the plane's release gate. The system uses information from the GPS and other instruments in the plane to determine wind speed and wind direction as well as other parameters.

Kimmel says the accuracy of the dry applications is high. “It automatically changes from applying 300 lbs./acre to 100 lbs., even if you're flying 140 mph,” he says.