Soil fertility expert Rasel Parvej addresses corn response to zinc fertilization at the 2024 Wheat and Oat Field Day, which was held at the at the LSU AgCenter Macon Ridge Research Station in Winnsboro. Photo by V. Todd Miller

Farmers are noted for being good stewards of the land. After all, the soil is where they plant and grow their crops for the purpose of earning a living. Many have the intention of passing it to the next generation, so taking care of the soil is of upmost importance.

Nitrogen used for fertilization purposes is one of the largest input costs for row crop producers. Because of the expense involved, using nitrogen efficiently is beneficial to the crop and the farmer’s pocketbook.

Sulfur is a plant-essential nutrient that helps increase nitrogen efficiency. Therefore, producers should test their soils for sulfur content.

Brenda Tubaña, a soil fertility specialist in the LSU AgCenter School of Plant, Environmental and Soil Sciences, has been studying sulfur to determine fertilization guidelines for grain production in Louisiana.

Tubaña’s research indicates the sulfur content in soil should be at least 10 ppm. For levels below this, she recommends producers add at least 20 pounds of sulfur per acre to avoid deficiencies. Generally, there is little residual sulfur left from the previous year’s application.

“We found that there is a minimal buildup of sulfur, even for those fertilized at high rates,” Tubaña said. “Sulfur is mobile in the soil, and it is not uncommon to lose it through leaching.”

The timing of the sulfur application is also a determinant, according to Tubaña.

“Our latest results showed a 19 bushel per acre increase in corn yield from side-dressing 70 units of nitrogen with 20 units of sulfur at the V6 stage,” she said.

Another area of fertility being studied by AgCenter scientists focuses on the role of micronutrients. These nutrients are needed in small amounts but are required for the production of energy and in combatting stress factors brought on by issues such as diseases.

Soil pH plays a major role in micronutrient deficiency. Soils with a pH between 6 and 6.8 are less likely to suffer from micronutrient deficiency, making managing soil pH vital.

AgCenter soil fertility scientist Rasel Parvej, stationed at the Macon Ridge Research Station near Winnsboro, performed a zinc fertilization trial in corn. He described it as the first time zinc has been studied in this manner.

“Zinc is a micronutrient, so if the pH goes higher, the availability of micronutrients becomes less and less except molybendum,” Parvej said. “If the pH level is 7 or above, the phosphorus binds with zinc creating phosphorus-induced zinc deficiency. Soil testing is very important to determine if you need to add zinc or not.”

Parvej is also reevaluating soil-test-based phosphorus (P) and potassium (K) fertilizer recommendations for corn across 15 sites at five different research stations. From last year's results, he found that P and K recommendations do not vary with soil types. Corn requires more P and K than the current recommendations in very low-testing soils, while no P and K fertilizer is needed in soils with more than 35 ppm Mehlich-3 P (70 lb P/acre) and 130 ppm Mehlich-3 K (260 lb K/acre) at a 0- to 6-inch soil depth.

Tubaña found in her research that a foliar application of multiple micronutrients as a tank mix (solution) was more yield positive than a suspension form. She did caution that an unnecessary application of some micronutrients may counteract the benefits of other micronutrients.

So, what does this mean? Tubaña said that soil or plant tissue testing could be used to select the appropriate micronutrient mixes.

Because of the complexity of soil fertility, there are many avenues of new research to pursue.

One area involves the use of biostimulants. They are designed to improve nutrient efficiency, increase tolerance to stress and strengthen quality traits. She will evaluate the performance of different biostimulants on the market.

Cover crops have been used to help increase soil organic matter. Tubaña and Parvej plan to look at long-term effects of cover cropping and biochar application on nutrient cycling and nutrient requirements for corn and soybean rotations.

Slow-release technology with regards to fertilization is being used more frequently. Both scientists plan to evaluate the source, timing and use of this technology in both soybean and corn.

Research in these areas is expected to be performed for four years before recommendations are made.