High levels of nitrate in food is undesirable, as it may be easily converted to nitrite, which is a well known carcinogenic compound that can also interfere with hemoglobin activity. The objective of this study was to evaluate the influence of different forms of N-fertilizer (cattle manure, urea and a mixture of both) on the N-NO3- concentration observed on leaf tissues of kale (Brassica oleracea var. acephala). A field experiment was conducted from March until August 1995, at the Embrapa-Agrobiology Research Center. The experiment was laid out in a randomized block design, with six treatments: cattle manure addition (20 t/ha), urea addition (900 kg/ha), mixtures of cattle manure (20 t/ha) with increasing urea levels (225, 450 and 900 kg/ha) and a control. A total of four replicates was used. The distance between plants in a row and between single rows was 0.6 m, and 0.8 m was the distance between double rows. A total of 24 plots with 9.6 m² each was used. Plants growing solely on cattle manure showed lower nitrate contents on leaf blades than those receiving additional urea (17.6 mg/g F. M. and 303 mg/g F. M.), respectively. Petiole N-NO3- contents for all treatments were three times higher than the ones observed in leaf blades (1830 and 561 mg/g F. M.), respectively. According to WHO, the Daily Acceptable Intake (DAI) for an adult weighting 65 kg is 53.3 mg of N-NO3-, which represents the maximum quantity this compound that can be swallowed daily, through food and water. From the results obtained, the DAI would be reached after consumption of 2.67 kg of kale (leaf blade) cultivated under cattle manure fertilization, or just 0.18 kg of kale cultivated under cattle manure and urea (111 kg/ha) fertilization, which approximates to the urea dosage recommended in the "Manual de Adubação de Rio de Janeiro". As a result of the lower nitrate contents found in kale growing solely on cattle manure, it was concluded that the cattle manure fertilization improved the quality of the product.
Brassica oleracea var. acephala; nitrogen; organic matter; carcinogenic compound
