The biggest driving force behind adopting precision agriculture technology is how quickly a farmer can recoup the investment costs of the equipment.

Ohio State University researchers, in an effort to provide information on the most accurate, cost-effective equipment on the market, have found global positioning guidance systems that not only have the potential to pay back to the user, but operate under minimal costs.

Reza Ehsani, an Ohio State extension precision agriculture state specialist and Matthew Sullivan, an Ohio State extension program specialist, have tested six commercially available differential global positioning system (GPS) guidance systems with WAAS (Wide Area Augmentation System) differential signal. WAAS is a GPS differential source originally provided by the Federal Aviation Administration in air travel that has the abilities to calculate accurate GPS correction signals for precision agriculture.

"In order for a GPS receiver to be accurate, one needs to have a differential source and there are three sources available to farmers: commercial satellite providers, Coast Guard beacon signals and a new source known as WAAS," says Ehsani. "GPS guidance systems are examples of how technology can pay back to the farmer and they are the quickest way of doing it that has been on the market so far."

The researchers believe WAAS may be advantageous in precision agriculture technology for a variety of reasons. The WAAS signal can be picked up throughout the North American continent and is free to use. In addition, WAAS uses the same signal frequency as the GPS signal and many guidance systems are available that operate with WAAS. In some cases, these systems are cheaper than GPS guidance systems that are using other differential correction sources. Coast Guard beacon signals are free, but are restricted to bodies of water and become degraded as the distance increases from the source. Commercial satellite providers charge an annual fee to use their signals.

"WAAS, we think at least in Ohio, is a very good differential GPS source for farmers. They can use it directly or as a backup to their current differential source" says Ehsani. "In our evaluations, we were interested to see how accurate GPS guidance systems with WAAS were and their cost-effectiveness."

Based upon research conducted in central Ohio, the researchers found that, 95% of the time, the systems had the accuracy of staying within 20" of the desired position when driving in a straight line. On a typical Ohio farming operation this 20" error can be expressed as a 2% overlap with a 90’ boom width compared to a possible 5-6% overlap with traditional foam markers.

"That's pretty good for farmers to conduct a variety of field work, from spraying to laying down fertilizer with a low percentage of overlap," says Sullivan. "And that 3% advantage over foam markers when spraying a 2,000 acre operation, for example, it means 60 acres less in overlap, potentially saving the farmer $900 in chemical applications at $15/acre/year. Plus taking into consideration the time and fuel the farmer saves and the wear and tear on his tractor."

Before purchasing any kind of guidance system, however, farmers are urged to make their own evaluations and shop around for the system that suits them best, depending on their farming situation and what features the guidance system offers. Such factors, say the researchers, do have an influence on the performance of the equipment and its overall effectiveness in the field.

The details of the study can be found at http://www.oardc.ohio-state.edu/fabe/precisionag/ .A list of the companies that participated in the study, as well as additional precision agriculture information on guidance system components and options, their benefits and tips for purchasing a particular system can also be found on the website.