Tubana up to challenge of focusing on fertility issues

Frances Gould, Gautreaux, Craig  |  11/20/2013 3:01:52 AM

Graduate students Marilyn Dalen and Yumiko Kanke, of the School of Plant, Environmental and Soil Sciences, measure the height of corn plants. The greenhouse study, which is designed to investigate phosphorus chemistry of soils where corn is grown, is part of a larger project on soil fertility issues in corn and soybean production being conducted by Dr. Brenda Tubaña. (Photo by Dr. Brenda Tubaña)

This field study in Winnsboro is evaluating the effects of lime, phosphorus and potassium applications on soybeans. (Photo by Dr. Donald Boquet)

Soil fertility issues can be challenging for both farmers and scientists. An issue with soil fertility in one field – or one part of a field – may not exist in another.

To compound fertility problems, a farmer may be producing crops on multiple soil types so that a single fertility program is not practical and generally will lead to erratic yields. For the scientists charged with finding the ideal fertility program, this task is proving to be a difficult one to conquer.

But Dr. Brenda S. Tubaña, an assistant professor in the LSU AgCenter’s School of Plant, Environmental and Soil Sciences, is up to the challenge. She is looking at soil fertility issues in corn and soybean production by examining what levels of essential nutrients are needed to maximize a farmer’s profits. She also is working to determine which fertilizer application levels maximize yields and yet are environmentally friendly.

Tubaña’s research involves a two-pronged approach. One involves traditional soil testing techniques to determine which nutrients are present and if the nutrients are at sufficient levels to optimize yields. The second method involves the use of an optical sensor that measures the green biomass of a plant.

"Fertilizer is a major production cost to farmers, especially in corn production. If we can determine that fertilizer applications can be reduced without affecting yields, then the farmer will benefit along with reducing the chance of runoff into nearby water bodies," Tubaña said.

The optical sensor approach involves "GreenSeeker" technology. A sensor generates a reading called the normalized difference vegetative index. This reading is then plugged into an equation that estimates if a second application of nitrogen is needed and, if so, the appropriate amount. The equation bases the nitrogen recommendation on in-season crop yield potential and available soil nitrogen.

"There has not been much change in the coefficient of the equation over past years, but we continue to collect data every year to update the equation," Tubaña said. "It takes a large amount of data to refine the equation and have confidence in it being reasonably accurate."

The remote sensor approach has a distinct advantage over traditional soil testing methods because the readings are instantaneous and the plant does not have to be destroyed for samples to be taken. It also is possible that remote sensing could have applications beyond soybean and corn production.

Most growers make two applications of nitrogen in their corn fields with the majority made in the initial application. Second applications generally are made around the V8 leaf stage.

Tubaña’s research is looking at using traditional soil nitrate test methods, optical sensor readings and yield/ goal approaches to see which methods are most successful in terms of yield and cost benefits to the producer.

Research also is looking at ways to account for the amount of nitrogen present in the soil. If researchers are able to develop a way to accurately analyze the existence of nitrogen in the soil, the amount of nitrogen fertilizer applied could be reduced. Complicating matters, however, is that soil types can influence the uptake of nutrients.

Tubaña says it is important to consider the soil’s capacity to supply nitrogen. This capacity is affected by the type of soil. Because of this condition, she is conducting her research at various LSU AgCenter locations across the state – the Macon Ridge Research Station near Winnsboro, the Red River Research Station near Bossier City and the Northeast Research Station near St. Joseph. She also has a research plot near Cheneyville in Rapides Parish.

These different locales give her a good representation of the different soil types found in the state. Because Tubaña’s research is done at multiple sites, she is assisted by LSU AgCenter research scientists Dr. Don Boquet, Dr. Rick Mascagni and Dr. John Kruse. Since these scientists are located near the research sites, their assistance is crucial to the success of the projects, she said.

Another fertility issue Tubaña is examining is the tendency for alluvial soils to be deficient in zinc. This zinc deficiency is aggravated by the antagonistic relationship between phosphorus and zinc, and the phosphorus found in these types of soils in ample amounts often is due to past applications for crop production.

Phosphorus interrupts the ability of plants to absorb zinc, which, in turn, influences crop yields. Tubaña hopes her project will deliver a fertilization management plan and recommendations for overcoming this issue.

Tubaña stresses the importance of producers conducting traditional soil tests to identify potential fertilization issues. For example, Tubaña say research has indicated that grain yields can be increased by adding phosphorus to soils that test below the critical level of 35 parts per million. She says soil testing can be one of the best nutrient management practices in crop production.
The success of Tubaña’s research would allow producers to have a plan that could maximize the effectiveness of their fertilizer applications, decrease their input costs and minimize the impact on the environment by reducing the amount of nitrates introduced into ground and surface waters. She believes the answers can be found, and she is getting closer with each research project.

Craig Gautreaux

2010-11 funding for these projects:
 $50,000 (corn/wheat and soybean)

(This article was published in the 2011 Louisiana Soybean & Grain Research & Promotion Board Report)

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