Dear Melson Jones as already correctly pointed out by the other RG members, citric acid cannot act as a nitrogen source because the molecule does not contain any nitrogen. Perhaps you have mistaken citric acid with another acid? In any case, ammonium sulfate should only be compared with other nitrogen-containing nutrients anf fertilizers such as e.g. ammonium nitrate. For some potentially useful information please have a look at the following literature reference:
Comparison of Ammonium Sulfate With Other Nitrogen and Sulfur Fertilizers in Increasing Crop Production and Minimizing Environmental Impact: A Review
Article Comparison of Ammonium Sulfate With Other Nitrogen and Sulfu...
Unfortunately this paper has not yet been posted as public full text on RG. Please check if you can access it through your institution.