Nitrogen management is probably the single most variable production input growers face in agriculture, and with the continued increase in fertilizer costs, application efficiency is becoming increasingly important.

In response to this need, Ohio State University soil research and Extension specialists are evaluating the use of optical sensors in nitrogen management.

“Nitrogen efficiency in crop production, such as corn, is estimated to be only about 33 percent, suggesting that under current nitrogen recommendation methods the majority of nitrogen applied is going elsewhere other than into the crop,” said Robert Mullen, an OSU Extension specialist with the Ohio Agricultural Research and Development Center, and an assistant professor for the School of Natural Resources. “On top of that, it’s becoming more of an economic penalty to over-apply nitrogen.”

Optical sensors that can be mounted on a tractor are being developed in an attempt to increase nitrogen efficiency by assessing a plant’s overall health using red and NIR (near infrared) light. Plants absorb red light during photosynthesis as an energy source. Therefore, healthy plants will absorb more red light and reflect higher amounts of NIR light than unhealthy plants.

By comparing the health status of the crop to a nitrogen-rich strip (an area in the field where the crop is responding to an environment high in nitrogen), growers can determine if the soil is providing adequate nitrogen or additional nitrogen needs to be applied.

“Current nitrogen recommendations assume four things: yield potential doesn’t vary year after year, the yield level the soil will support without supplemental nitrogen is negligible, pre-plant nitrogen will be available throughout the growing season, and soil uniformity produces similar yield results across the field,” said Mullen. “Growers know that none of these assumptions are entirely accurate, and they can potentially be avoided using optical sensors.”

There are challenges to using such technology, however, said Mullen.

“Optical sensors are an indirect assessment of soil fertility because it is using plants to give an indication of how well that soil is supporting the crop,” said Mullen. “There is also a wildcard in this technology with making recommendations and improving efficiency. And that’s if there will be federal dollars available for growers to adopt it.”

Using optical sensors in crop production is nothing new in the United States. Oklahoma State University spearheaded research and development of an optical sensor variable rate application system, which is being used and evaluated in the Western Corn Belt.

Such technology, however, is new to Ohio, and Mullen hopes the Ohio State project, funded through a Fluid Fertilizer Foundation grant, will provide some relevance for Ohio growers.