Enhancing nitrate and ammonium recovery from lettuce leaves: evaluating the impact of cultivation practices and chemical extractants

This study aimed to identify what affects mineral nitrogen (N) levels in lettuce by testing how different chemicals extract nitrate and ammonium, using continuous flow analysis for measurement. The study's rationale is to explore how agricultural methods and environmental factors impact the nutrition and safety of leafy greens. In this research, we utilized a collection of lettuce leaf samples obtained from our earlier investigation. The study involved examining different cultivars cultivated in diverse fields or greenhouse settings, using organic or conventional fertilizers, to observe the outcomes. To measure the amount of ammonium in leaf tissue, we assessed extraction solutions of 0.001, 0.01, 0.1, 1.0, and 2.0 M potassium chloride (KCl), along with distilled water. These evaluations were conducted using leaves from 16 different lettuce plants cultivated under various production conditions. To quantify nitrate, extracting solutions of 0.01 M calcium chloride (CaCl2), 2% acetic acid, and distilled water with two contact times (15 and 45 min) were evaluated. Increasing contact time increased the recovery of nitrate. Distilled water and calcium chloride were significantly more effective in extracting nitrate than acetic acid. No significant difference occurred between water and the salt solution to extract nitrate from leaf tissue. Moreover, the result revealed that 0.01 M KCl extractant satisfies the recovery of ammonium from the leaves regardless of cultivar, fertilizer source, or amount of N application.