Is it worthwhile adding sulfur this soybean season? Growers want to know.
From application recommendations to the evidence behind sulfur’s benefits, our in-house agronomist, Mercedes Gearhart, gets a lot of questions. We’re sharing the answers to the most common questions she receives about ammonium sulfate.
How important is sulfur for soybeans?
In one word: very.
Soybeans require plant-available sulfur all season long, starting in the early growth stages. Sulfur is key to protein and chlorophyll formation. Without it, nodulation cannot occur, and without nodulation, there is no biological nitrogen fixation, a process essential for growing soybeans economically.
This is due to soybeans’ high protein content, which means they require four to five pounds of nitrogen per bushel, compared to about one pound of nitrogen for a bushel of corn. Growers need to ensure sufficient sulfur to support nodulation.
After all, even soils with high organic levels cannot satisfy that requirement, given the slow mineralization rates under the prevailing cooler temperatures of the spring season. Thus, sulfur supplements are necessary.
The traditionally sulfur-responsive soils are coarse and low in organic matter. However, heavier soils with higher organic matter may still be unable to meet today’s sulfur demands due to reduced atmospheric sulfur deposition and higher-yielding crop genetics.
Why should I use ammonium sulfate instead of other sources of sulfur?
Ammonium sulfate fertilizer is readily soluble in water, meaning that its nitrogen and sulfur contents are available with the first rain. On the other hand, elemental sulfur is insoluble in water and must undergo oxidation before becoming available to the plant.
In temperate climates, it can take up to three years for elemental sulfur to oxidize.
An additional advantage of applying ammonium sulfate, even at the modest rates of 80 to 100 lb/acre, is the temporary and localized acidifying effect in situ or nearly in situ at the roots. This can help improve the solubility of phosphorus, another macronutrient particularly important for early growth of soybeans because of its role in cell multiplication.
This localized acidification can also improve the solubility of boron, manganese, copper and zinc present in the soil, which are known essential micronutrients for plants.
Can ammonium sulfate protect my crops against diseases, including Sudden Death Syndrome (SDS)?
Growers understand that planting early comes with wetter, colder spring temperatures (e.g., below 50°F). These lower temperatures encourage the growth of Fusarium fungi, which is known to cause SDS.
Ongoing studies at Purdue suggest that ammonium sulfate can help mitigate SDS and help prevent or alleviate other soil-borne diseases, such as Phytophthora.
What results have soybean growers seen with ammonium sulfate?
Over the past few years, AdvanSix has partnered with several soybean growers to field-test ammonium sulfate on the crops. We asked them to compare ammonium sulfate-treated and untreated soybeans throughout the entire season, with trials varying by region and crop rotation.
One grower in Pennsylvania reported that his ammonium sulfate-treated sections of the soybean field had an average yield of 88.5 bu/ac, while the untreated sections only yielded an average of 82 bu/ac. Another grower in Missouri reported that his treated acres yielded an average of 64.5 bu/ac, while the untreated acres yielded only 55.6 bu/ac.
It is notable that those fields are in very different environments and conditions, yet both benefited. You can read about these two trials in detail here.
Do you have a specific question about ammonium sulfate or an application question? Click here to Ask the Agronomist or visit soybeans.advansix.com.