Supplying soybeans and other plants with the nutrients they need to thrive is crucial for producing a profitable crop.

Brenda Tubaña, an LSU AgCenter soil fertility specialist, compares the nutrient management of crops to humans eating a proper diet.

“It’s like you and me,” said Tubaña, who is the Jack E. and Henrietta Jones Professor in the School of Plant, Environmental and Soil Sciences. “If you are healthy and you are getting enough nutrition, you are not going to get sick.”

Examining sulfur and beneficial microorganisms

Since its passage in 1970, the federal Clean Air Act has limited air pollution in the United States, but it also has lessened the amount of sulfur in the atmosphere, leading to unintended changes to certain crops.

“The high amount of sulfur that we got from precipitation and the atmosphere in the past years is no longer present,” Tubaña said. “So, we started to see cases of sulfur deficiency.”

Corn, soybeans and wheat require sulfur, so producers must add it to their fertilizer programs. Tubaña is studying sources of sulfur available to producers and also reviewing LSU AgCenter fertilization guidelines and soil testing procedures.

As part of the study on sulfur fertilization, a graduate student working with Tubaña researched beneficial microorganisms in the soil that could enhance plant health. The researchers were seeking to enhance a beneficial microorganism in the soil that would help recycle nutrients and release plant-promoting enzymes, Tubaña said.

The graduate student, Jayvee Cruz, a doctoral student in the School of Plant, Environmental and Soil Sciences, studied Louisiana crops and identified microorganisms that thrive in Louisiana soil. She identified microorganisms, silicate-solubilizing bacteria, that could transform silicon in soil to a plant-usable form and assist in nitrogen fixation and release enzymes from the soil that can be taken up by plants.

Micronutrient treatments

Tubaña also leads a team of AgCenter researchers working to improve the delivery of micronutrients for Louisiana field crops to improve yield and lessen disease pressure.

Tubaña is evaluating foliar nutrient treatments that can be applied in a suspension — a cloudy mixture composed of larger particles — rather than in a solution, which is typically made of smaller particles.

“The advantage of having it in suspension over solution is that the suspension contains micronutrients in a higher concentration,” Tubaña said.

Using foliar treatments in suspension form may also save producers money, she said.

The researchers have tested the suspensions of molybdenum, copper, boron, manganese and zinc against solutions of the nutrients in stands of corn and wheat and have begun testing on soybeans.

While micronutrient deficiencies are not common, Tubaña said, manganese and zinc deficiencies can be induced in some conditions, such as when producers use glyphosate to control weeds.

Micronutrients are also the focus of research by soil chemist Jim Wang. For three years Wang’s lab has studied the effects of molybdenum, iron and boron on soybean production. This year Wang is also studying the micronutrient manganese.

In acidic soils with lower pH levels, molybdenum can bind to iron and aluminum oxides and can transform into an insoluble compound that cannot be taken up by the soybean plant, he said.

Small applications of molybdenum in soil or foliar treatments can lead to large yield increases in these situations, Wang said. In trials, soil applications of molybdenum in acidic soils led to an average of an 11% increase in yield. Foliar applications led to a 17.4% increase.

Producers can have a difficult time understanding their molybdenum levels, Wang said.

“There is no good soil testing for molybdenum,” he said.

In some Louisiana soils with higher pH levels, such as Red River alluvium, Wang’s research has focused on boron and iron. Trials have shown an increase of 4% to 12% in yield after applying iron chelates, which are types of iron treated to make the nutrient more readily available to plants. Wang has specifically studied the iron chelate Fe-EDDHA.

In these alkaline soils, Wang has seen a 12% yield increase after applications of boron. However, knowing the soil pH is crucial because the application could easily cause a toxic effect for soils with a pH level lower than 7.