Ammonium is a positively charged ion, or cation, with the chemical formula NH4+. It is formed when ammonia (NH3) accepts a proton (H+). Ammonium is commonly found in nature, especially in soil and water, where it plays a crucial role in the nitrogen cycle, helping plants absorb nitrogen for growth. In addition to its natural occurrence, ammonium is used in various applications, including fertilizers, cleaning products, and food preservation. It is important in agriculture as it provides a readily available source of nitrogen, which is essential for plant development and crop yield.