Midrib Nitrate Concentration as a Means for Determining Nitrogen Needs of Cabbage

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 N_O3-N concentration for cabbage (Brassica oleracea L., capitata group) during the growing season. Tissue samples for nitrate analysis were taken from cabbage 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 N_O3-N concentration determination. A high degree of correlation existed between NO3-N concentration in cabbage midribs at various sampling dates and yield as determined by stepwise regression analysis. Nitrate-N concentration in cabbage midribs indicated the N status of the plant. Minimum or critical levels of NO3-N in cabbage 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, 8000 mg kg-1; folding, 6000 mg kg-1; early head, 4000 mg kg-1; preharvest, 3000 mg kg-1.