Diurnal variation in the nitrate content of parsley foliage

Abstract

The diurnal fluctuation of nitrate concentration in the foliage of three parsley subspecies (plainleafed, curly-leafed and turnip rooted parsley) cultivated in the spring and autumn of two consecutive years was examined. Nitrogen was applied at 30 (Control), 75, 150, 300 mg kg -1 in both years, but with the addition of 450 mg kg -1 in year 2. Harvest was carried out at 08:30, 12:30 and 17:30 on a single day for each sowing. The results showed that the nitrate concentration of the foliage was lowest when harvest was carried out at midday (12:30), although not always to a statistically significant level in the low N-application rates (≤ 75 mg kg -1 ). In addition, increasing the rate of N application from 30 to 450 mg kg -1 resulted in a progressive increase in the nitrate concentration of the foliage irrespective of the time of day at which the plants were harvested. The concentration of nitrate differed between subspecies and was higher in the older, outer leaves in the case of turnip-rooted parsley than in the younger, inner leaves. It is concluded that although the nitrate concentration of the foliage of all three parsley subspecies increased with increasing rates of N-application, even the implement of the highest nitrogen rate (< 400 mg kg -1 fresh weight), did not resulted in nitrate content that exceeded the maximum level recommended by the E.U., irrespective of the time of harvest, subspecies, age of the leaves and the season of cultivation.