Many of John Williams' photography subjects are bare - bare fields, that is.

Williams, who owns Ag Traks, Inc., a crop consulting firm at Holdrege, NE, uses aerial photography to help him decide the best way to soil sample.

"Each field has its own personality, and you need to study that personality when deciding on a pattern for soil sampling," says Williams. He's also owner of The Precision Partners Corp., an alliance that provides precision farming consulting and services to other consultants, fertilizer retailers and producers.

Williams' basic program is to sample a field annually on 20- to 40-acre grids. The actual size depends on a field's individual characteristics. He samples annually so his clients can manage nitrogen more precisely.

"To enhance that basic program, we take bare-soil aerial photos of fields in the spring right after planting," says Williams. "If we see something in a photo that looks suspicious, we go to that spot or spots - using GPS for guidance - and do more intensive soil sampling in the spring or fall.

"In some cases we have found fertility deficiencies, and in those situations we try to correct them while the crop is still small," Williams explains. "If that's not possible, we correct them before the next crop is planted, and that normally will be the case until we master variable-rate technology in this area."

Williams might also find a problem not related to fertility.

"It might be compaction or poor drainage, for example. But the aerial photo, combined with our intensive scouting and field histories, helps us detect it."

During the growing season, Williams takes up to five or six additional aerial photos. They're used for guidance in field scouting.

"Most growers want three aerial photos - bare ground, at corn canopy and prior to tasseling," he says. "Not all our clients are involved as yet, but the interest is growing."

After harvest - for clients who yield map - he overlays one or more of the aerial photos on a yield map to determine if low-yield spots coincide with suspicious areas on the aerial photo(s). If so, the problem could be fertility or some other cause. He then goes to those spots for a closer look.

"If the problem is fertility, we may begin soil sampling more intensively, in grids of 1-5 acres, but usually 2 1/2 acres - to determine just how much fertility variability there is in that particular field," says Williams.

"In other words, we start with 20- to 40-acre samples and then narrow it down, if need be, according to the specific field. In that way we are not doing unnecessary soil sampling and needlessly running up a client's costs."