Building soybean fertility is a process that starts from the ground up. With the potential for higher soybean yields with each passing year, the need for a strong, healthy crop continues to rise. Soybeans have more complex nutrient needs than previously thought and require nutrients throughout the growing season.
As a secondary nutrient, sulfur (S) plays a critical role in the growth and development of high-yielding soybeans:
Necessary for optimum growth during the vegetative and reproductive stages
Required to fixate nitrogen from the soil
Plays a large role in soybean seed development and the photosynthesis process
A part of every living cell and is important to the formation of proteins
One of the difficult things with sulfur is that it’s often found in insufficient quantities for the needs of high-yielding crops, which is where supplementing becomes important.
Types of Sulfur, Soil Behavior, and Crop Needs
There are two types of sulfur used for fertilizer applications: sulfate sulfur and elemental sulfur. Sulfate sulfur (SO₄²⁻) is the form of sulfur needed for crop uptake whereas elemental sulfur (S⁰) is not plant-available and must be converted by microbes in the soil into the available sulfate form. Lower contributions of sulfur from precipitation and organic matter coupled with higher yields have led to an increased need for proper sulfur nutrition. Like nitrate nitrogen, sulfate sulfur is especially prone to leaching in soils with low cation exchange capacities and/or environments with high rainfall. Elemental sulfur often takes weeks or even months to convert to sulfate and cannot meet early-season nutrient demands.
Data published from the University of Illinois highlight the need for season-long sulfur availability in soybeans, stating that the greatest demand for sulfur occurs in the weeks around seed filling, with uptake rates of more than 0.25 lbs. of sulfur per acre per day. Research has also shown that during peak growth, an acre of soybeans can take up nearly 17 pounds of fertilizer each day. Proper soybean fertility can have a profound effect on yields and quality. It can also improve soil health, as proper nutrition helps to increase the soil’s organic matter, leading to improved yields over time.
Season-Long Sulfur Availability
Balanced crop nutrition is critical in the early, mid-season and late growing phases of soybeans, further demonstrating the need for a fertilization plan that will provide season-long nutrient availability. The most effective sulfur management plan should include early- and late-season availability. Sulfate sulfur is available immediately to the crop while elemental sulfur oxidizes for late-season availability. Selecting a fertilizer source for preplant applications that provides both early- and late-season sulfur nutrition ensures a healthy crop and successful growing season.
Measuring Nutrient Success
Properly nourished soybeans will “canopy” quicker, have a higher resistance to insect and disease pressure throughout the season and will likely begin to flower and set pods earlier. Visual inspections of growth stages between R3-R5 can provide a good indicator of a properly balanced fertilizer program in soybeans. Often overlooked in a nutritional plan, sulfur can increase pod set and pod fill, leading to higher yields.
A Fertilizer Source with Two Forms of Sulfur
As you discuss balanced crop nutrition options with your agronomist or crop advisor, look for a fertilizer technology that provides superior phosphate nutrition and season-long sulfur availability, like MicroEssentials® from The Mosaic Company. Having two forms of sulfur built into each granule will provide better sulfur distribution to feed crops during early-season vegetative growth and late-season pod fill.
Recent trials conducted by third-party researchers indicate that using MicroEssentials S10® increased soybean yield by 2.3 bushel/acre over diammonium phosphate (DAP). The full study can be viewed here: www.cropnutrition.com/resource-library/microessentials-s10-vs-dap-soybean
A recent preplant broadcast application also demonstrated that replacing a small amount of MOP with K-Mag® increased soybean yield by 2.2 bushel/acre when averaged across 22 trials. The full study can be viewed here: www.cropnutrition.com/resource-library/k-mag-blend-study
Talk to your crop nutrition advisor or agronomist to discuss how sulfur can aid in your yield goals.