After growing winter wheat, Louisiana farmers wishing to plant a second crop have few options. The most popular choice is soybeans, and an LSU AgCenter researcher is studying several factors that could help producers achieve higher yields or save money on their crop inputs.

Lisa Fultz, a soil microbiologist in the School of Plant, Environmental and Soil Sciences, is evaluating soybean maturity groups, examining irrigation management and determining benefits of supplemental fertilizer applications and the timing of the fertilization.

Ongoing since 2015, the project is conducted at three AgCenter sites — the Macon Ridge Research Station near Winnsboro, the Red River Research Station near Bossier City and the Dean Lee Research and Extension Center near Alexandria.

“The two main nutrients we are evaluating at are sulfur and potassium. The project is looking at both rates and timing of the potassium applications,” Fultz said.

One question growers have after harvesting wheat is how to manage the wheat residue in the field after harvest. One option is to simply leave the residue and plant soybeans behind it. Many growers choose to burn the residue and then plant soybeans.

Fultz says this project could provide growers the answer of how to specifically manage this residue in regard to working with soybeans in maturity Groups IV and V.

Her findings at the Macon Ridge location found no differences in yields between soybean maturity groups in fields that were planted in residue or after burning. However, at the Dean Lee location, the Group V beans did have significantly higher yields than Group IV beans in unburned fields.

Fultz’ research indicated that wheat yields also increased slightly in fields that were burned the previous year regardless of the two maturity groups planted.

The second objective focused on sulfur management in the form of urea and ammonium sulfate. The project also looked at potassium to see if the timing of the application triggered increased yields.

Urea and ammonium sulfate were applied in split treatment on wheat. The applications consisted of five different combinations. They were:

• 100 percent urea.
• 66 percent urea/33 ammonium sulfate.
• 50 percent urea/50 percent ammonium sulfate.
• 33 percent urea/66 percent ammonium sulfate.
• 100 percent ammonium sulfate.

Potassium was applied at three different times: at planting, at in-season nitrogen applications and after the wheat harvest.

The nutrient management findings indicated no significant difference in yield for soybeans or wheat. Fultz did see an increase in wheat yields with the 33 percent urea/66 percent ammonium sulfate fertilization rate, but she also reported a decrease in soybean yields with this combination.

The final objective focused on irrigation management. This research was only conducted at the LSU AgCenter Red River Research Station near Bossier City. Four treatment groups were used in the study, and they were: control (no irrigation), full-season irrigation, irrigation at the early reproductive stage and irrigation at the pod elongation stage.

Similar to the nutrient findings, there were no yield responses to the irrigation study. Fultz did point out that this was from the initial test, and differences may occur in future work.

Craig Gautreaux