Updating Petiole Nitrate-Based N Fertilizer Recommendations for Arizona Cotton

In-season petiole nitrate (NO₃) has historically been used in the western US in cotton to guide N fertilizer management.  However, this data has not been updated in > 20 years, for new management practices and current cotton cultivars. The first objective of this study was to assess in-season cotton petiole NO₃ as affected by various N fertilizer rates to sprinkler-irrigated and furrow-irrigated cotton in Maricopa, and Safford, Arizona, respectively.  The second objective was to compare petiole NO₃ with leaf N and chlorophyll meter readings.  Our final objective was to update University of Arizona N fertilizer recommendations based on petiole NO₃.  Samples were taken at from mid-June to early August from twelve plants per plot.  Petiole-NO₃-N levels began the season very high (i.e. 25-30,000 ppm), and showed a sharp declining pattern as plant took up N.  Zero-N plots went deficient by early bloom.  This data will be highly useful in updating University of Arizona N fertilizer recommendations.