Nitrogen is a key limiting nutrient in soils with low fertility, requiring its replenishment through fertilizers. Several sources of nitrogen are available on the market, and the choice of fertilizer depends on soil characteristics, climatic conditions, and most importantly, economic viability. This chapter aims to discuss the importance of nitrogen (N), its relationship with organic matter, its dynamics and losses in the pasture soil system, the primary sources of nitrogen, and strategies for effective fertilization management.