Cotton petiole analysis for soluble nitrate-nitrogen (NO₃-N) can be a powerful tool in fertilizer management but many sources of variability exist which can cloud the interpretation of analysis results. A general trend from high NO₃-N levels to low as the cotton plant develops has been previously found but reported results indicate that a substantial decrease occurs during intensive flowering. Other results indicate that younger petioles from the same plant have lower NO₃-N levels than more mature petioles, making consistent petiole selection essential. An intensive sampling program in a single field with a uniform soil showed a 10-fold change in NO₃-N levels in different ares of the field.