In the past decade, a group of additives and other treatments called biostimulants, which claim to enhance the use of nutrients in crops, has seen a boom in the marketplace.

Agricultural producers have embraced this new class of materials, but they question which products they should use for different crops, said Brenda Tubaña, a soil fertility researcher with the LSU AgCenter.

Last year, Tubaña and her research team are studying these types of treatments. They are assembling the biostimulant products most commonly used by Louisiana producers and testing them, Tubaña said.

“This project came about because we want to document their performance based on soil and plant parameters including yield, so that when growers ask me if this product is working, we can pull out information to help them make a decision,” Tubaña said.

Biostimulants include a wide range of products. They may be made from bacterial and microbial inoculants, biochemicals, humic and fulvic acid, or seaweed extracts, according to manufacturers that produce them.

“In agricultural production, there's a wide landscape of biologicals, and that includes biostimulants,” Tubaña said. “By definition itself, and it's still changing right now, these are materials that are either fortified with microorganisms or some organic materials that enhances the efficacy of applied fertilizer.”

The 2018 farm bill stated that a biostimulant was “a substance or microorganism that, when applied to seeds, plants or the rhizosphere, stimulates natural processes to enhance or benefit nutrient uptake, nutrient efficiency, tolerance to abiotic stress, or crop quality and yield.”

Some biostimulants “claim they can fix atmospheric nitrogen, adding nitrogen supply to crops like wheat or corn. This may not be as beneficial to soybean,” Tubaña said. Other biostimulants contain microorganisms that help make precipitated nutrients in the soil soluble and available for the plant.

For the biostimulant study, Tubaña and her team bought popular products or asked companies to send them samples. In some cases, they asked producers for leftover products to test.

Biostimulants could become more important in the future in view of depleting mineral deposits, Tubaña said. Phosphorus fertilizer, for example, is produced from rock phosphate, she said, and feldspar is mined for potassium fertilizer.

“These minerals have finite sources,” she said. “While the phosphate rock deposit is plentiful, only a small amount of phosphorus can be economically extracted. If you keep mining the easily extractable minerals, perhaps 50 years from now, we may not have these resources.”

Tubaña and her team are studying additional soil fertility avenues as well. One long-term project documents the effects of cover cropping, slow-release fertilizers and biochar on fields.

Cover crops collect nutrients while they grow, and after the crop is terminated and incorporated into the soil, the nutrients are released back to the soil to be used for the main crop corn or soybeans.

“There's a long list of benefits of cover crops — soil surface protection, increases soil organic matter content, nutrient recycling,” Tubaña said.

The cover cropping study began in 2018. Now, Tubaña is seeing an increase in yield of 2 to 3 bushels per acre and soil sulfur and phosphorus content.

“This may not be a big return in terms of yields,” she said. “But the long-term practice of cover cropping helps out in raising the level of plant essential nutrients in the soil and overall soil fertility.”

Applying biochar to fields has similar effects, Tubaña said. Biochar, which is the partially combusted residue of various materials, has been used as a soil amendment for years, according to the U.S. Department of Agriculture.

In Louisiana, biochar from sugarcane bagasse is common, and Tubaña has applied this form of biochar on fields with microorganisms added. She is working to determine the optimal application rate, and her research so far showed 1/2 to 2 tons per acre.

“These are practices that do not bring benefits overnight,” she said. “It takes years of practice before you start seeing the benefits, especially when you're looking at nutrient cycling and buildup of organic matter in the soil.”

Representatives of companies that produce biostimulants observe the trials begun by Brenda Tubaña’s research team. Photo provided by Brenda Tubaña

Biostimulants are sprayed at a field trial undertaken by Brenda Tubaña’s soil health research team. Photo provided by Brenda Tubaña

On a research plot, Brenda Tubaña’s soil health team is testing several biostimulant products. Photo provided by Brenda Tubaña