Nitrogen, potassium, and phosphorous are the main ingredients in synthetic fertilizer. These are elements and are the same no matter the source. The nitrogen in synthetic fertilizer comes from the air, and the potassium and phosphorous come from rocks. Barley (and perhaps alfalfa) contain additional chemicals that reduce algae. Nothing wrong with using organic fertilizer but I recommend against manure for health reasons. The issue with organic fertilizer sources is that their chemical makeup varies from batch to batch and knowing what you add can be difficult, as can replicating results over time.
