Is Variable Rate Application For You?

Is Variable Rate Application For You?

As precision agriculture practices drift closer and closer to the mainstream with each passing year, cotton producers around the country are taking notice.

One of the first management techniques many consider is variable rate application (VRA) – a broad umbrella under which a host of inputs of varying costs could be applied. The practice, after all, is based on a seemingly common sense principle – that all the acres on a farm are not created equally. Variations in soil type, nutrient availability and water scenarios provide a wide range of maximum production levels a piece of ground could ultimately reach.


So how, then, should a cotton producer get started in this increasingly popular precision management practice? Should he or she even get started in it at all? Precision experts from around the Cotton Belt say the latter question is the first one that should be considered.

“I’d be hesitant to make a blanket statement that everyone should immediately give VRA a try,” says John Fulton, associate professor and Extension specialist at Auburn University. “One of the things we focus on is that we believe a farm is a business operation. From that, VRA can be one component of that business, but the first thing someone should consider is ‘What benefit am I trying to achieve by implementing a VRA program?’ You might find that you are not ready for it right now.”

To be sure, Fulton believes VRA could provide benefits in almost every scenario, given time. But, as he points out, in some instances growers turn to VRA as a practice that can immediately provide savings on inputs, only to later find that their precision fertility program might actually suggest spending more on input costs.

“All of a sudden they say, ‘Well it’s not working for me.’ Well, that may not have been the right approach if you were trying to save costs immediately,” Fulton says. “But if you’re looking at a business model to invest in getting yourself to the next level in five or ten years, then in time you’ll find that it is a good business decision, and you’ll make money from it.”

Fulton also points out that VRA is a practice that few farmers have the resources or capabilities to execute on their own; especially small farms. Growers may have to bring in outside assistance or invest in new farm management software technology for generating prescription maps and conducting soil samples, for example. Ultimately, he says, growers need to have a clear idea of what they are getting themselves into when they choose to jump into VRA practices.

Making the Jump into VRA

But for those who have a clear cut business objective and have determined that VRA is the right practice to accomplish that goal, the time has never been better to begin the practice. Some common technologies that are widely available today can lend themselves to getting started in VRA. In fact, experts say, all it takes is access to the Internet to begin looking for the variability on your farm.

“Look at your fields with a tool like Google Maps to see if there are a lot of patterns in the images to get an idea of how much variability may be present,” says Dr. Ed Barnes, director of agricultural research at Cotton Incorporated. “If there is a lot of variation present in the image, then a grower likely needs to consider variable rate application.”

Many longtime cotton growers around the Cotton Belt are just recently getting a glimpse at the soil variation in their own cotton fields for the first time, now that some equipment companies are packaging yield monitors standard with their new harvest equipment.

“A more robust (and complicated) way to check for variability is to take advantage of yield maps,” says Barnes. “New pickers and combines all have the equipment installed.  Just looking at the variation in yield in a field should give a producer an idea of how much variability there is and how much it may be costing them.”

Once variability is established (and Barnes suggests soil variability is ever-present in every corner of the Cotton Belt), there are some VRA scenarios that can pay quick dividends for cotton producers. Barnes points to section-control sprayers, which work through GPS for guidance and automatically shut off parts of a spray boom when it ventures outside of a field’s boundary.

“The cost of the system is low and typically pays for itself in a year – especially for someone with oddly shaped fields,” says Barnes.

As for the actual inputs that can provide quick savings for cotton producers, Fulton and Barnes say lime lends itself well to variable rate applications.

“Growers implementing precision soil sampling have found that better ways to manage their inputs exist,” says Fulton. “They’ve been able to identify pH issues, which for them have been a quick pay back. Getting your lime within that optimal range has been something of a corrective measure. Precision sampling followed by a variable rate application of lime is a pretty quick pay back for them from a yield perspective.”

Fulton says many of his growers in Alabama have found substantial savings by using VRA with phosphorus, especially in light of rising fertilizer costs.

“There’s no reason to be applying a lot of phosphorus if the plants aren’t going to be able to take advantage of it,” says Fulton. “And some have found benefits on the potassium side, as well.”

And when it comes to fertilizer applications, Barnes says there are methods of VRA that are more attractive to growers who may be wanting to try the precision practice for the first time.

“Try variable rate, pre-plant fertilizer (P & K) through a local dealer who offers the service,” Barnes says.  “This way, growers can see some of the data and potential benefits without a big time investment. And if they use lime, definitely go variable rate. It almost always has a positive return on investment if there is any variability in the field.”

Barnes also notes that there are products on the market, such as GreenSeeker from Trimble that allow growers to practice VRA without pre-existing field maps. These real-time sensor-based systems diagnose the characteristics of a field as they pass over them, carried along by in-field farm equipment.