Ammonium Sulfate: Better Than the Alternative


For over a century, ammonium sulfate (AMS) has been a trusted and reliable fertilizer providing the most readily available nitrogen (N) and sulfur (S) nutrients to the crop and making it an efficient option for farmers. Recently, a granular biosolid-enriched ammonium sulfate (Bio/AMS) claiming to be a slow-release N and S fertilizer entered the market. While performance data is limited for this new product, a recent study comparing AMS to Bio/AMS (trade name SymTRX™) by three renowned scientists has clearly demonstrated that AMS remains the most efficient N and S containing fertilizer option for farmers.

The research results were published in the July/August 2021 issue of Agronomy Journal (Vol 113, Issue 4, pages 3578-3585) and includes the following studies: (a) characterize the chemical composition of the Bio/AMS material, (b) examine the movements of N and S through soil leaching columns, (c) determine N release over time using soil incubation studies, (d) examine ammonia (NH3) volatilization as affected by the sources, and (e) evaluate the availability of S and N for plant growth in a greenhouse study conducted with canola and wheat.

AMS vs. Bio/AMS
Below is an overview of the results obtained from just a few of the studies conducted comparing traditional AMS and Bio/AMS fertilizer.

  • SymTRX fertilizer is merely a physical mixture of AMS and biosolids. The ratio of water-soluble NH4-N/SO4-S of the SymTRX fertilizer was 0.86 and the AMS fertilizer was 0.87. This indicates that the water-soluble N and S compounds in the SymTRX fertilizer were derived from the same N and S source as the AMS fertilizer.
  • SymTRX fertilizer, like AMS fertilizer, does not fit the typical release curve expected from a slow-release N fertilizer. When comparing the SymTRX fertilizer with a typical slow-release fertilizer by the AOAC adopted technique, only 15% of total N was released from the typical slow-release N fertilizer compared to 60% from the SymTRX fertilizer in the first 7 days. Only 50% of total N was released from the typical slow-release N fertilizer compared to 78% from the SymTRX fertilizer in 28 days. Furthermore, N continued to be released slowly from the typical slow-release N fertilizer from 7 to 56 days without reaching the plateau, while the SymTRX attained maximum release between 26 to 56 days.
  • SymTRX and AMS fertilizers are similar in the rate of N release and transformation in the soil. There were no significant differences in KCl-extractable ammonium (NH4-N) from the SymTRX and AMS fertilizers, and only a small amount of nitrate (NO3-N) derived from the total 250 mg N kg-1 applied with either the SymTRX or AMS fertilizer based on soil incubation studies. Like the AMS fertilizer, the SymTRX fertilizer does not behave as a slow N-release fertilizer in the soil.
  • Both AMS and SymTRX behaved similarly in NH3volatilization on alkaline soil. The amounts of NH3–N volatilized by the end of the study were <5% of total N applied when both the SymTRX and AMS products were applied to the alkaline Brownfield soil (pH 8.5) whereas 35% of total N volatilized from the urea-N treatment. There were no significant differences in the amounts of NH3–N volatilized from SymTRX vs. AMS.
  • SymTRX fertilizer acted like the AMS fertilizer in providing S to the canola crop and N to the wheat crop. In the canola study, there was a significant biomass yield response to S but no significant difference between the two sources in either the Brownfield or Lakeland soils. Separately, in the wheat study, there were no significant differences in N uptake between the SymTRX and AMS fertilizers as described by the same curvilinear response for Ashland soil and the same linear response for Manhattan soil.

The study results show that the SymTRX fertilizer has no significant agronomic benefits over AMS, as evidenced from canola and wheat crops in greenhouse studies. The study also shows that AMS provides more nutrition to the crops than SymTRX. With a nutrient density of 45%, the AMS fertilizer delivers approximately 20% more nutrition to the crops for each pound of fertilizer applied as compared to the SymTRX fertilizer with a 37% nutrient density, making the AMS fertilizer a much more efficient source of nutrition to the crop on a pound-for-pound basis.

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