NITRATE CONCENTRATION IN TWO COMMERCIAL TYPES OF LETTUCE (Lactuca sativa L.) GROWN WITH DIFFERENT NITROGEN SOURCES

Abstract

Nitrate (NO3 -) can transform into nitrite (NO2 -) in the human body and nitrites can change normal hemoglobin to methemoglobin, contributing to the formation of carcinogenic nitrosamines. Lettuce is one of the vegetables with a high capacity to accumulate nitrates. The objective of this study was to evaluate the response of lettuce to increasing doses of nitrogen applied as urea and the addition of vermicompost on the nitrate leaf content of two commercial types of lettuce: cv. Daguan (butterhead) and cv. Brisa (loose-leaf). Two field trials were conducted simultaneously in two growing seasons: autumn-winter and spring. One trial consisted of compost 24 t ha-1 vermicompost-(L1) added and a control treatment (L0) with no amendment, while the other treatment consisted of 75 kg N ha-1 (N1) and 150 kg N ha-1 (N2) applied as urea, also with a control treatment without fertilization (N0). The experimental design was a randomized complete block, split-plot design with four replications. Nitrate concentration was measured by colorimetry during growth and harvest. A decreasing level of nitrate concentration was observed in both trials during the winter period. Nitrate concentration was influenced by genotype, fertilization treatments and seasons. A higher level of nitrates was observed in the vermicompost treatment with ‘Brisa’ in both seasons. In the autumn-winter season, ‘Brisa’ presented a higher response to urea application, recording higher levels of nitrates at harvest compared to ‘Daguan’. No response to fertilization was observed in the spring and only the treatment consisting of 150 kg N ha-1 (N2) in ‘Brisa’ resulted in higher leaf nitrate content at harvest.