Calibration of a petiole sap nitrate test for irrigated ‘russet Burbank’ potato

Abstract

Portable electrodes for rapid quantitative determination of nitrate‐N (NO₃‐N) in plant sap have recently been developed, thus enabling a quick assessment of the crop nitrogen (N) status. The intent of this study was to provide diagnostic criteria necessary for the interpretation of petiole sap NO₃‐N concentrations for potato (Solanum tuberosum L.). Specific objectives were to characterize the relationship between potato petiole sap NO₃‐N concentration and petiole NO₃‐N determined by conventional dry weight analysis, and to establish NO₃‐N sufficiency ranges (NSR) for irrigated potatoes based on sap analyses associated with maximum and 85–95% of maximum yield. A four‐year experiment was conducted on a loamy sand soil (Udic haploboroll) at the Sand Plain Research Farm, Becker, Minn. Ten treatments consisting of various rates and times of N application were evaluated. Recently matured leaves were collected every 10 to 14 days, and petioles were split for sap NO₃ and dry tissue NO₃ analysis. Two portable NO₃ electrodes, the Cardy and Hach meters, designed for quick tests, and a fixed laboratory method, the Wescan, were used to determine sap NO₃‐N concentrations. Dry petiole NO₃‐N and petiole sap NO₃‐N were linearly and significantly related, with regression coefficients r²=0.91, 0.92, and 0.93 for the Cardy, Hach, and Wescan methods, respectively. Nitrate‐N sufficiency ranges determined with the Cardy were 50 mg L^‐1 higher than those determined with the Hach. During the vegetative/tuber initiation stage (15–30 days after emergence), NSR were 1350–1450, and 1300–1400 mg L^‐1 for the Cardy and Hach, respectively. As the season progressed, the NSR decreased. During the tuber bulking period (30–75 days after emergence), NSR were 600–1350 mg L^‐1 for the Cardy and 550–1300 mg L^‐1 for the Hach. At maturity, NSR were less than 600 and 550 mg L^‐1 for the same respective electrodes. Petiole sap NO₃‐N determined by either the Cardy or Hach methods can be a quick and useful tool to assess potato N status.

Notes

Corresponding author (e‐mail address: [email protected]).