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Plant analysis has been used to evaluate the nutritional status of many crops for diagnostic and corrective purposes. This study was initiated to establish critical nitrogen (N) plant tissue levels using midrib NO3-N concentration for cauliflower (Brassica oleracea L., var. Botrytis) during the growing season. Tissue samples for nitrate analysis were taken from cauliflower plants over a period of four growing seasons beginning at the 4 to 6 leaf stage of growth and biweekly through pre-harvest. The midrib from the most recently full sized leaf was sampled for NO3-N concentration determination.

A high degree of correlation existed between NO3-N concentration in cauliflower midribs at various sampling dates and yield as determined by stepwise regression analysis. Nitrate-N concentration in cauliflower midribs indicated the N status of the plant. Minimum or critical levels of NO3-N in cauliflower midribs for sampling dates throughout the growing season were established for conditions such as are found in the desert regions of Arizona as follows: 4 to 6 leaves, 11,000 mg kg-1; 10 to 12 leaves, 9000 mg kg-1; folding, 7000 mg kg-1; early head, 6000 mg kg-1; full size head 2500 mg kg-1; pre-harvest, 1500 mg kg-1.