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Fluid Journal : Fluid Journal 1993-1995
percent by volume of alkaline ATS without an appropriate pH buffer (e.g., APP) can increase pH of the UAN and reduce the benefits of ATS in curbing ammonia loss. ATS also can interfere with some methods of determining residual urea in soils. Nitrification slowed ATS can slow nitrification when banded with UAN. As with urease, effects of ATS do not equal those of specific nitrification inhibitors. ATS, when added to UAN, increased the amount of residual ammonium in the soil four weeks after fertilizer application. Note the effect of the ATS was not as strong as for nitrapyrin. Thus, ATS should not be seen as a replacement for specific nitrifica- tion inhibitors. The UAN or UAN-ATS treatment was injected before planting spring wheat in North Dakota. In some laboratory studies, use of thiosulfate has produced a temporary nitrite accumulation in the soil. But this has not been confirmed under field conditions. P more available Recent research has shown that banding ATS with phosphorus can improve phos- phate uptake by crops. Figure 4 shows a greater uptake of phosphate by wheat when fertilized with APP-ATS than with APP alone. The fertilizer was applied in an alkaline loam soil. In other trials, we ob- served that other acid-forming fluid S fertilizers (ammonium sulfate, ammonium bisulfite, and potassium thiosulfate) also enhanced P uptake. So, this effect is not specific for ATS. In a study from Canada, barley or rapeseed showed a large response to phosphate when a MAP solution and ATS were banded either together or separately on an alkaline soil. However, the largest response occurred when they were banded together. Precautions While the primary justification for ATS is its convenience as an S source for users of fluid fertilizers, a couple of precautions need mentioning. One is its short-term phytotoxicity. For example, it should not be placed in direct contact with the seed of row crops. The other is it should not be used for foliar fertilization. Dr. Goos is associate professor in the Department of Soil Science at North Dakota State University. 20 15 10 5 0 APP+ATS APP alone 50 mg, 25 mg S/pot 0 1 2 3 4 Weeks of crop uptake Figure 2. Effect of ATS on uptake of P from APP by wheat, Goos and Johnson. P uptake by wheat - mg/pot Spring 1995
Fluid Journal 1996-1998