Evaluation of a rapid method for plant sap nitrate analysis

Abstract

A rapid method of analysis of nitrate in plant sap using Merck test strips was evaluated. Accuracy and precision of the strips was acceptable in a test in which aqueous samples were tested by 4 operators. Nitrate N was measured in 5 vegetable crops [carrot, celery, potato, sweet corn and tomato] at 2 stages of growth by 2 methods: squeezing sap from fresh petiole or stem tissue with NO3-N determination by Merck test strip; and acetic acid extraction from dried petiole or stem tissue with NO3-N determination by autoanalyzer. The relationship between the 2 methods was highly significant with coefficient of determination exceeding 0.82 in 8 of 10 cases (crops .times. sampling dates). When the strip results were corrected for moisture content the relationship with the laboratory method improved in most cases.