Scientists try optical sensors to determine nitrogen rates in corn

Kenneth Gautreaux, Tubana, Brenda S.  |  7/17/2012 10:05:54 PM

LSU AgCenter county agents R.L. Frazier and Dennis Burns apply fertilizer to a corn field near Epps, La., based upon vegetative readings supplied by GreenSeeker sensors located on the spray rig. The sensors record how much vegetation is present, and the amount of fertilizer applied is adjusted based upon this reading. (Photo by Brenda Tubaña)

Brenda Tubaña, an LSU AgCenter assistant professor in the School of Plant, Environmental and Soil Sciences, adjusts sensors used to measure the amount of vegetation in a corn field. The instantaneous reading is sent to a computer that then determines the appropriate amount of fertilizer to apply while a spray rig travels through the field. (Photo by Craig Gautreaux. Click on image for downloadable version.)

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News Release Distributed 07/17/12

LSU AgCenter scientists are looking at new technology for determining nitrogen rates in corn involving an optical sensor reading approach based upon vegetative data.

“This is a good time because the corn plant stand is established with vegetation not so thick to reach canopy closure,” said Brenda Tubaña, an assistant professor in the School of Plant, Environmental and Soil Sciences in Baton Rouge.

The brand name for the sensor is GreenSeeker, and the approach is a sensor-based nitrogen management system that looks at the plant at the V8 or eight-leaf stage. Tubaña places four sensors across the arms of a spray rig that covers a 30-foot swath across the field.

“The sensors give an instantaneous reading. This reading is then used to determine the amount of nitrogen that can be dribbled or injected into the ground,” she said.

The reading is called the normalized difference vegetative index (NDVI). The NDVI is then plugged into an equation used to determine the amount of nitrogen needed in the second application.

“The equation changes slightly as more information is gathered,” Tubaña said.

Tubaña is comparing this approach with two more traditional ways to determine nitrogen rates: the farmer’s standard rate of applying nitrogen based on the farmer’s perception of potential need (yield-goal approach) and the recommended amount of nitrogen based upon a soil nitrates sample.

This year, with assistance from Madison Parish extension agent R.L. Frazier and Tensas extension agent Dennis Burns, Tubaña was able to put all three methods to the test in corn fields located near Tallulah and Epps.

“I’m excited to see what will be the outcome in a farmer’s field. It will provide us with some real answers,” Tubaña said.

Tubaña continues to conduct research on zinc deficiency in alluvial soils with John Kruse, state extension specialist for corn and cotton stationed at the Dean Lee Research Station in Alexandria.

Compounding the zinc deficiency problem is that some soils have a buildup of phosphorus from previous seasons of corn production that inhibits the absorption of zinc.

Tubaña has had success in increasing corn yields in Red River alluvial soils. She has found that adding 2.5 to 5 pounds of zinc per acre to soils with 2 parts per million or less of zinc made a significant impact on yields.

In a trial plot in Bossier Parish, yields increased 20 percent. In Rapides Parish near the town of Cheneyville, she had a greater success with yields increasing nearly 30 percent.

Craig Gautreaux

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