A new way to make topographic maps could help farmers use variable-rate fertilizer application to maximize returns, says James McKinion, a USDA scientist.

With maps fed into computerized, variable-rate fertilizer applicators, farmers can direct more fertilizer to the highest-yielding zones and the least to the lowest-yielding zones. They can also use these zone maps to make other decisions, such as planting more drought-tolerant varieties in low-yield zones or reducing planting populations.

Five years of comparing these maps and actual “on-the-go” yield monitoring for corn and cotton on a farm in Mississippi showed that accurate yield predictions can be made based on topography.

McKinion who is an electronics engineer at the USDA’s Genetics And Precision Agriculture Research Unit at Mississippi State University., did the study with USDA entomologist Jeff Willers and geneticist Johnie Jenkins.

The researchers had a plane with LIDAR (light detection and ranging) sensors fly over the 1,000 rolling acres of the farm in Mississippi.

LIDAR is a form of radar that can map elevations digitally, showing slopes and sun exposures, by bouncing laser light off the landscape. One advantage of LIDAR landscape mapping is that it only has to be done once.

By blending yield results with the maps, the scientists divided fields into high, medium and low-yield zones. The LIDAR topographic mapping is spreading from state to state. For example, Louisiana, for has financed LIDAR mapping of the entire state.

It’s expensive for an individual farmer to pay for LIDAR mapping, so McKinion is also looking for alternative techniques for topographic mapping. For more information, e-mail McKinion at: James.McKinion@ars.usda.gov or phone (662) 320-7449