A PETIOLE SAP NITRATE TEST FOR CAULIFLOWER

This study was conducted to evaluate the accuracy of sap analysis usin g a portable nitrate ion meter for cauliflower (Brassica oleracea L. B otrytis Group, cv. Candid Charm) petiole nitrate determination. The re lationship between NO3-N concentration in fresh petiole sap and in dri ed petiole tissue was studied for cauliflower grown in southern Arizon a during the 1993-94 and 1994-95 growing seasons. Experiments were fac torial combinations of three water rates and four N rates, both rangin g from deficient to excessive. Petioles were collected throughout each season and were split for analysis of sap NO3-N and dried petiole NO3 -N. Linear correlations between the two methods were similar in both s easons, with no consistent effect due to water application rate or cro p maturity. Therefore, a single regression equation was derived: petio le sap NO3-N (mg . liter(-1)) = 0.047 x dry petiole NO3-N (mg . kg(-1) ) + 218 (r(2)=0.772). This equation can be used to relate sap test mea surements to existing guidelines for NO3-N concentrations in cauliflow er petioles. These results suggest that the quick sap test, using the portable nitrate ion meter, is a valuable technique for monitoring N s tatus of cauliflower.