Yield monitors are coming on nearly as fast as mosquitoes after a wet spell. And a good share are equipped with GPS receivers, which allow for yield-mapping capability.

Combine manufacturers, many crop consultants and various agribusinesses offer yield-mapping services. In some cases, the services are free.

Is a farmer who has a computer better off to do the mapping himself or have someone else do it?

It depends on your situation and personal preferences, experts say. Soybean Digest talked with three growers, each of whom takes a different route.

Mark Wilson and his father, Dave, raise corn, soybeans and hogs at Toulon, IL. Mark has been using a computer for farm accounting, sow feeding and hog production records for more than 10 years. But he chooses not to do his own yield maps.

"We've had a yield monitor and GPS for the past three years," says Mark. "In 1996 we used the Case IH free service for yield and moisture maps. The last two years we had our crop consultant, Mowers Soil-Testing Plus, do the maps."

Wilson lists these reasons:"For one, Mowers has the experience and expertise. They do maps for many of their clients."

"Second, they do our fertility work and crop scouting. Therefore, they can layer various other maps, such as fertility or weeds, on our yield maps to see how they relate and to help us in analyzing the yield maps.

"And third, we simply don't have the time to handle the hog business and other farm responsibilities and also do the yield mapping.

"They are doing what they do best and we focus on where we can get the best return on our time and knowledge," Wilson points out.

John Ryan, Harmon, IL, who has had a yield monitor/GPS for the past four years, has always done his own mapping. He currently uses Farmworks geographic information system (GIS) software.

Besides yield and moisture maps, he can track yield by soil type, elevation, pH, organic matter and other factors. For instance, if he has a field with two major soil types, he can make a map that shows the average yield for each.

"Primarily, I do my own mapping because I can manipulate the data in various ways and gain a better understanding of what it means," he explains. "For example, I can work with the yield ranges and view just those areas where soybeans are in the 50-bu range. By zeroing in on a specific yield range I get more insight on why those areas are yielding as they are."

Another reason Ryan does his own maps is that he can process the PC card each night and produce a map for that day's harvest.

"It can indicate whether I had an equipment problem, such as with the flow sensor, moisture sensor, antennae cables or receiving device," he says. "And I can correct the problem before I get any more corrupt data."

Ryan says the daily mapping also lets him get readings on how certain hybrids or varieties are yielding, and to note how moistures are running, which helps him manage his drying system.

What's more, doing his own maps means he is sole owner of his data.

"In total, you just have more flexibility and control when you process your own maps, and it only takes a few minutes," says Ryan.

Robert Boston and his b rother Harry, Earlville, IL, have most of their yield maps made by Case IH. But the Bostons, who have had a yield monitor and GPS for the past four years, also do some of their own.

"I download data from our yield monitor PC card to a floppy disk each night and then at the end of harvest we send the floppies to Case," says Robert. "Within about two weeks we receive high-quality maps in a nice binder. They are very professional looking."

At those times when Robert wants immediate yield data on a particular field - maybe to see how certain hybrids or varieties are performing - he makes his own maps using Case software.

"The maps are easy to generate," he says. "You can make one in 15 to 20 minutes. When we make our own maps we can customize them to look however we want. For example, we may want to make up different yield categories than are on the maps that are made for us."