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Abstract
A rapid test for measuring petiole sap nitrate‐N in potatoes was developed using a pH/ISE meter equipped with a nitrate‐ion specific electrode. Nitrate‐N measurements were made on fresh sap that was diluted with a solution of 0.075M Al2(SO4)3‐18H2O and 0.02M H3BO3. The sap nitrate‐N concentration, as determined by the rapid test, was highly correlated (r = 0.91, P<0.01) with dry matter nitrate‐N. Because of the non‐clogging design properties of the electrode used, this test procedure produced rapid and reliable results with good instrument stability and long electrode life. The chemicals used for this test are relatively non‐hazardous and the required tools can be assembled into a small portable kit. When properly calibrated, this test will provide added impetus to growers to rely on tissue analysis for corrective in‐season nitrogen (N) fertilization of potatoes.