It’s Not Too Late To Topdress AMS


Ammonium sulfate (AMS) is a tried-and-true fertilizer that can provide a readily available source of sulfur and nitrogen throughout the growing season. With flexible application options, AMS can be applied pre-plant, at planting or even topdressed to give plants the nutrients they need to develop and grow when they need them most.   

While AMS pre-plant or applications at planting are most common in the United States, there are some scenarios in which a topdress application is warranted.  

“I think an environment that creates a stressed crop is the top reason for a topdress application of AMS,” said Jason Magan, plant nutrients sales manager at AdvanSix. “Cool, wet weather and cold soils are some of the most common conditions that can cause the crop to be stressed because the organic soil-based nutrients won’t become available in these conditions. This is where a rescue topdress application comes in to give the crop a quick pickup of nitrogen and sulfur to replenish the nutrients for the crop and keep it going.”  

 Tissue sampling can also help determine if a boost of sulfur and nitrogen is needed. If the nitrogen-to-sulfur ratio is 18:1 or higher, a supplemental sulfur application is recommended for many crops. This additional sulfur can be supplied by topdressing AMS, particularly if potential soybean yield exceeds 70 bu/ac. Biological fixation of nitrogen from the air covers only about half of a soybean crop’s nitrogen needs, with the rest derived from the soil.  

Timing a topdress application  

According to Magan, key time frames for topdressing include R2-R4 for soybeans and V5-V6 and VT for corn. 

“Because the crop is pulling so many nutrients out of the soil to put to that grain-fill in corn or pod-fill in soybeans, a little additional AMS as feed for the plant doesn’t hurt it,” Magan said. “I think anytime out there ahead of tasseling or flowering is a good time for AMS to give the crop an extra push on the sulfur side.”  

Planning ahead 

If the conditions are right or tissue sampling indicates a need for a topdress application of AMS, Magan advises growers and retailers to plan ahead to ensure supply. 

“In a normal year, you probably need to be planning two to three weeks ahead of a topdress application,” Magan said. “On a year like this, you may need three to four weeks. With the current state of the Mississippi River logistics, it may take a little longer to get the product in place.”  

Benefits of topdressing AMS  

Overall, the greatest benefit of topdressing AMS is the readily available nitrogen and sulfur it supplies to the crop during the key nutrient uptake periods for crops. Due to reduced atmospheric deposition of sulfur with low industrial and automotive emissions in recent decades, supplemental sulfur is required to maximize yield potential in today’s higher-yielding crop production systems. Topdressing in the early reproductive stages helps ensure the crop has the sulfur and nitrogen it needs for grain-fill later in the season.   

“Whether it’s soybeans, corn, rice or any other high-yielding crop, they all need more sulfur today than they ever have before,” Magan said. “Topdressing is a relatively efficient way to create that sense of insurance on the crop, just to make sure you get that little extra boost of nitrogen and sulfur when the crop needs it.”  

Contact your ammonium sulfate supplier or visit to learn more.