Nitrogen (N) is an essential element for plant growth and reproduction, and management is critical for optimal yield in Iowa corn production systems. It is involved in many important plant biochemical processes, such as photosynthesis, and plant components such as amino acids, proteins, and chlorophyll. Plants require N to produce the chlorophyll used in photosynthesis; and it’s chlorophyll that gives plants their green color. Plants growing with an adequate supply of N have a dark green color; if N is deficient plants are less green, and yellow in color, lack vigorous growth, and have reduced yield. Legumes like alfalfa and soybean host specific rhizobia bacteria common in Iowa soils which capture atmospheric N gas and convert it into plant available N. Legume crops very rarely require N fertilization; however, cereal crops–like corn–do not have symbiotic fixation. They rely on N from the soil, or N applied in manure or as commercial fertilizer for optimal growth and production. With corn being an important and widely grown crop in Iowa, adequate N supply is critical to achieve high yield and economic profitability.