Establishment of Critical Sap and Soil Nitrate Concentrations using a Cardy Nitrate Meter for Two Carrot Cultivars Grown on Organic and Mineral Soil

Abstract

Nitrate (NO₃ ⁻) meters have been used effectively for crop nitrogen (N) management in many crops, including corn and cabbage. The use of a Cardy NO₃ ⁻ meter to assess the N status of the carrot crop could improve the utilization of applied N, but critical NO₃‐N concentrations are required. Two carrot cultivars were grown on mineral and organic soils over 3 years at five N application rates to establish critical sap and soil NO₃‐N concentrations and to identify the effects of soil type and cultivar. Although a yield response to N application occurred on mineral soil in 2 of 3 years, consistent critical sap NO₃‐N concentrations could not be established because of variability among years, cultivars, and soil types. Critical soil nitrate concentrations were highly variable, but values of 31 to 36 mg · L⁻¹ NO₃‐N could be established for the early sampling date to 30 cm deep. Sap NO₃‐N concentrations cannot be used alone for N analysis of carrots, but early‐season soil NO₃‐N assessment could be useful in adjusting N‐fertilization practices.

Keywords:

• Carrot
• critical concentrations
• cultivar evaluation
• mineral soil
• nitrate
• nitrogen
• organic soil

Acknowledgments

The authors thank Kevin Vander Kooi, Marilyn Hovius, and the staff of the Muck Crops Research Station for their assistance. Funding for this project was provided by the Agricultural Adaptation Council through the support of the Ontario Fruit and Vegetable Growers Association, the Ontario Ministry of Agriculture, Food and Rural Affairs/University of Guelph Plant Program, and the Natural Sciences and Engineering Research Council of Canada.