Assessment of a Nitrate Meter for Nitrogen Tests in Mineral and Organic Soils

Abstract

Nutrient management legislation in Ontario, Canada, has prompted an evaluation of alternative nitrogen (N) management techniques. Rapid, accurate methods of assessing soil nitrogen are required to assist in N management. A portable nitrate (NO₃ ⁻ meter (Cardy) was evaluated for use in testing soil N for vegetable crops grown on organic and mineral soils. Cabbage, carrots, and onions were grown on both soils in Ontario, Canada, in 2000 and 2001. Nitrogen was applied at five rates to cabbage and carrots, and three rates to onions ranging from 0 to 200% of current provincial recommended N rates. At three growth stages throughout the growing season, soil samples were collected and subdivided. One subsample was used for Cardy meter analysis, and the other for laboratory analysis of NO₃-N. Cardy NO3-N readings overestimated laboratory results in most instances on mineral soil, but consistently underestimated laboratory results on organic soil. A conversion factor would be required for both soil types, and 10 or more samples should be analyzed from a particular field to reduce variability. Soil NO3-N readings were variable among years and crops. Compared with laboratory analysis, Cardy soil test results are available in a fraction of the time required for laboratory results and are less expensive when analyzing over 100 samples. Yield was assessed at harvest. Yields were generally unaffected by N rate, except in cabbage in 2000, suggesting that adequate N was present in most treatments. The Cardy meter is effective in determining N sufficiency or deficiency in the field. The Cardy NO₃ ⁻ meter has potential as a field soil N test to supplement a nutrient management system for vegetable crops as long as region-specific recommendations are established.

Key Words:

• Cardy meters
• ion selective electrode
• nutrient management
• soil analysis