Extension agents Dennis Burns, left, in Tensas Parish, and R.L. Frazier, in Madison Parish, work closely with Brenda Tubaña, soil scientist, testing the validity of optical sensor-based nitrogen recommendations. The four GreenSeeker optical sensors are mounted on the front of a high-clearance tractor to allow the precise amount of nitrogen fertilizer to be applied plant by plant rather than a uniform amount across the entire field. (Photo by Brenda Tubaña)

Brenda Tubaña, LSU AgCenter soil scientist, tests the GreenSeeker technology with cotton. Dennis Burns, extension agent in Tensas Parish, is driving the high-clearance tractor. The four GreenSeeker optical sensors are mounted in the front of the tractor. (Photo by Bruce Schultz)

News Release Distributed 08/05/13

BATON ROUGE, La. – Nitrogen fertilizer is one of the biggest expenses faced by corn growers. Finding the appropriate amount to apply so no more is used than necessary is the goal of research by LSU AgCenter soil scientist Brenda Tubaña.

“It is mistakenly perceived that applying a high rate of nitrogen assures high yields. But this entails some major drawbacks,” she said.

First is the cost of the fertilizer, which can be unpredictable because if its dependence on fuel prices.

“A yield improvement may be outweighed by the cost of additional nitrogen unnecessarily applied,” she said.

Even if the fertilizer cost is inexpensive, applying too much can lead to yield reductions because of increased lodging and delayed plant maturity.

“Most important, excessive nitrogen fertilizer on agricultural land poses threats to the environment and human health,” Tubaña said.

A thorough soil test analysis is the first step corn growers must take to develop a fertilization plan that will help obtain favorable results both in yield and economic return.

“For light-textured soils, such as those alluvial soils on or near levees, tests should be conducted at least every other year,” Tubaña said. “The pH and nutrient composition of these soils can change rather quickly.”

For heavier soils, Tubaña recommends performing soil tests every three or four years.

Tubaña is conducting research looking at different nitrogen rates as well as the timing of the applications. Typically, nitrogen is applied in a split application. The first application is applied before or at planting with the amount representing 50-75 percent of the total nitrogen used on the crop. The rest is applied when corn reaches 3-12 inches tall.

Tubaña is studying the rates for the second application when the plant reaches the eight- to nine-leaf stage, which is when corn begins to take up a significant amount of nitrogen.

She is using optical sensor technology – the brand name is GreenSeeker – which involves taking readings from the crop’s canopy in the field to determine precisely how much nitrogen is needed. The farmer can then apply variable rates of nitrogen based upon the individual plant’s needs rather than a uniform application across the field.

This approach would reduce farmer’s costs and decrease the amount of nitrogen being lost into the environment through volatilization, runoff into water bodies or leaching through the soil.

The findings from her studies so far show improvement in corn nitrogen use efficiency. However, this does not necessarily translate into higher net returns.

“Both crop prices and nitrogen fertilizer costs must be considered in the continual effort to refine the sensor-based nitrogen decision tool,” Tubaña said.

Tubaña’s research on crop fertilization rates is partially funded by the Louisiana Soybean and Grain Research and Promotion Board.

Craig Gautreaux