A Petiole Sap Nitrate Test for Cauliflower

This study was conducted to evaluate the accuracy of sap analysis using a portable nitrate ion meter for cauliflower ( Brassica oleracea L. Botrytis Group, cv. Candid Charm) petiole nitrate determination. The relationship between NO 3 -N concentration in fresh petiole sap and in dried petiole tissue was studied for cauliflower grown in southern Arizona during the 1993–94 and 1994–95 growing seasons. Experiments were factorial combinations of three water rates and four N rates, both ranging from deficient to excessive. Petioles were collected throughout each season and were split for analysis of sap NO 3 -N and dried petiole NO 3 -N. Linear correlations between the two methods were similar in both seasons, with no consistent effect due to water application rate or crop maturity. Therefore, a single regression equation was derived: petiole sap NO 3 -N (mg·liter –1 ) = 0.047 × dry petiole NO 3 -N (mg·kg –1 ) + 218 (r 2 = 0.772). This equation can be used to relate sap test measurements to existing guidelines for NO 3 -N concentrations in cauliflower petioles. These results suggest that the quick sap test, using the portable nitrate ion meter, is a valuable technique for monitoring N status of cauliflower.