Which of the following salts is NOT used to provide nitrogen in fertilizers?

The correct answer is potassium nitrate (KNO3), as it is primarily used to provide potassium and nitrate ions, rather than nitrogen. While the compound does contain nitrate, which can contribute to nitrogen availability, its main role in fertilizers is to supply potassium, an essential macronutrient for plant growth, which aids in processes like photosynthesis and water regulation.

Ammonium nitrate, ammonium phosphate, and ammonium sulfate are all specifically formulated to deliver nitrogen to plants. Ammonium nitrate contains both ammonium and nitrate forms of nitrogen, making it a highly effective nitrogen source. Ammonium phosphate contributes nitrogen in the form of ammonium (NH4), while also supplying phosphorus (P), which is vital for root development and energy transfer processes in plants. Ammonium sulfate provides nitrogen in a sulfate form, which also helps improve soil acidity and nutrient uptake.

In this context, potassium nitrate stands out as the only choice that is not primarily aimed at providing nitrogen.