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Fluid Journal : Fluid Journal 1993-1995
!∀# %# &# ∋(() ∗ ∗ ∗ ∗ ∗+,- +./ 01 23456)/ ,1 271∀ 8 +,- +./ 0123456)/ ,1271∀ 8 +,- +./ 0123456)/ ,1271∀ 8 +,- +./ 0123456)/ ,1271∀ 8 +,- +./ 0123456)/ ,1271∀ 8/∀ /∀ /∀ /∀ /∀34249/∀ 34249/∀ 34249/∀ 34249/∀ 34249/∀ %/)/:∀;./∀ ;43/) <:3: 3.:3 </=(>)3∀:3/ 3./ =1245?/>/743) (7 3.4) ≅:21:?2/ )1271∀ )(1∀;/# Summary: Ammonium thiosulfate is a widely used fluid source of nitrogen and sulfur. It oxidizes rapidly. When mixed with other fluid fertilizers and applied to the soil in concentrated fertilizer bands, ammonium thiosulfate can enhance micronutrient availability, slow soil urease, slow nitrifi- cation, and improve the availability of P fertilizers. Ammonium thiosulfate is used for its convenience and other beneficial interactions. Ammonium thiosulfate (ATS 12-0-0-26S) is a standard product of the U.S. fluid fertilizer industry. Over the past 30 years, sales of ATS have steadily increased owing to its natural advantages: • compatibility with most fluid NPK sources • more rapid oxidation than el emental sources • higher analysis than other fluid sulfur (S) sources. Primary justification for use of ATS is the adding of S to fluid fertilizers. However, research over the past 20 years has also revealed that ATS, particularly when banded, may have other indirect benefits. Micronutrients more available Because ATS is both a reducing and acidifying agent, it can improve the avail- ability of iron and manganese in the soil. As a reducing agent, it donates electrons to other substances. As an acidifying agent, it works through oxidation by soil microbes. When the ATS is fully oxidized, nitric and sulfuric acids are produced in the soil. The ability of ATS to improve iron availability has been clearly shown in research. Figure 1 shows that banding a ferrous sulfate-APP suspension with ATS in an alkaline soil was effective in increasing Fe uptake by sorghum. The study further revealed that when ATS was banded in direct contact with the sorghum seed, germination and seedling damage resulted. Normal plant growth occurred when the ATS was placed two inches to the side and two inches below the seed. Research also has shown ATS enhances Mn availability. ATS reacts rapidly and abiotically with Mn-oxides in the soil, producing Mn2+ . Agronomists or growers who work in regions of Mn deficiency, or where Mn fertilization helps reduce certain crop diseases, are encouraged to experiment with ATS. Soil urease slowed ATS can slow soil urease when mixed with UAN and surface banded (dribbled). Urease is an enzyme that converts urea and water to ammonia and carbon dioxide. If surface-applied urea is hydrolyzed too quickly, part of the ammonia produced can leak back into the atmosphere and be lost. ATS is not a strong inhibitor of urease when compared to specific urease inhibitors such as NBPT. However, mixing ATS with UAN and applying in a band can slow urea hydrolysis significantly. Research also has shown that the strength of ATS as a urease inhibitor can be enhanced with large fertilizer droplets and at lower water con- tents. Figure 1 shows how adding 5 percent ATS by volume to UAN or UAN-APP mixtures slowed but did not prevent ammonia loss. Note also that the banded solutions performed much better than those broadcast. Where ATS was added and the fertilizer was banded, ammonia loss was reduced more than 60 percent! Other research, while also successful, has shown that loss reductions can vary widely among soil types. Inattention to details has and can cause problems. For example, some commercial ATS products are alkaline, with a strong odor of free ammonia. Adding more than 5 UAN + APP (Spray) UAN + APP + ATS (Spray) UAN + APP (Dribble) UAN + APP + ATS (Dribble) Ammonia loss -- lbs/A of N 15 10 5 00 7 14 Days after fertilization Figure 1. Effect of ammonia volatilization of placement and adding ATS to UAN- APP mixture on a Fargo-clay soil under field conditions, Fairlie and Goos. Spring 1995
Fluid Journal 1996-1998