Corn plants need adequate nitrogen (N) at all stages of growth to attain their yield potential. Meeting N requirements can be a management challenge when weather conditions promote losses of N early in the season and high plant demand for N later in the season. Chlorophyll meters can be used to detect deficiencies in N at any stage of growth. These meters are hand-held devices that measure the plant greenness when clamped on leaves. N-deficient plants have low concentrations of chlorophyll and, therefore, less greenness.