The best replacement for ammonium sulfate is ammonium nitrate.

The best alternatives to ammonium sulfate are rated as following:
★★★★★  ammonium nitrate
★★★★★  urea
★★★  aluminum sulfate
★★  ammonium persulfate
★★  ammonium thiosulfate
★  ironite
  ammonium nitrate fertilizer

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Speaking about ammonium sulfate, one probably shouldn't forget about roundup.

Other search terms related to ammonium sulfate and their ratings are:

★★★★★ roundup
★★★★ barium nitrate
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ammonium sulfate
ammonium nitrate