Evaluation of the nitrate text in folhosas hortaliças produced by different systems of culture. / Avaliação do teor de nitrato em hortaliças folhosas produzidas por diferentes sistemas de cultivo.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

Nitrate is naturally present in vegetables as a nitrogen source for their growth, the amount depending on genetic factors, the availability of this nutrient for the plant and environmental factors. It has been estimated that more than 70% of the nitrate ingested daily by man is supplied by vegetables. The present work evaluated the nitrate content in leafy vegetables (watercress, lettuce and arugula) produced by different systems of cultivation (conventional, organic and hydroponic). The daily nitrate ingestion from the consumption of these vegetables by the population was also evaluated. Sampling was carried out during the period from June/2001 to February/2003, the vegetables being acquired directly from producers, from markets and supermarkets from Campinas, São Paulo. Nitrate was extracted from the samples using the procedure recommended by AOAC. A flow injection analysis (FIA) spectrophotometric method was used for the nitrate determination of the ternary complex FeSCNNO+ at 460 nm. A difference was verified (P<0.05) amongst the three systems of cultivation for the average nitrate content in lettuce and arugula, the level found in the organic system being lower than that in conventional culture which in turn, was lower than that in the hydroponic system. For the watercress samples no difference (P<0.05) was found between the organic and hydroponic cultivated samples, both presenting higher nitrate contents (P<0.05) than the conventionally cultivated samples. The nitrate content for each vegetable species varied between producers, between different parts of the plant and in relation to the season. Of the vegetables examined in this study, those cultivated by hydroponics were responsible for the higher contribution to nitrate ingestion, representing about 8.6% of the value for the acceptable daily intake (ADI) established for this ion (3,7 mg of ion nitrate kg-1 of body weight day-1). The effect of the nitrate concentration in the nutrient solution and of the season on the accumulation of nitrate in lettuce cultivated by hydroponics was also verified. The plants were submitted to three treatments: nutrient solution recommended by the manufacturer, containing 152 mg/L of nitrate (NS), NS minus 25% m/v of nitrate (NS-25) and NS plus 25% m/v of nitrate (NS+25). The assays were carried out in February/March (summer) and July/August (winter) of 2002. In the summer, a difference (P<0.05) between the three treatments was verified, the average nitrate content in the lettuces cultivated in the NS+25 being higher than that of those cultivated in the NS which was higher than those cultivated in NS-25. This behavior was not shown in the winter season, where the average nitrate content did not differ (P<0.05) between the treatments. A difference (P<0.05) was found in the nitrate content between the lettuces cultivated in the summer and those cultivated in the winter, except for those cultivated in the NS solution. The plants cultivated in NS-25 solution presented a greater accumulation of nitrate in the winter, whereas those cultivated in the NS+25 solution showed a lower content of this ion in the winter than in the summer. In the summer, a reduction in the nitrate concentration in the nutrient solution (NS-25) was detrimental to growth, color and leaf uniformity of the plants. In the winter, excess nitrate in the nutrient solution (NS+25) inhibited the accumulation of this ion in the plant, as well as harming its growth. These results indicate the importance of controlling the nitrate content of the nutrient solution in the hydroponics cultivation system. The nitrate content in the vegetables was dependent on the cultivation system, the part of the plant and the season when they were cultivated. Leafy vegetables cultivated hydroponically present a higher nitrate content than those produced by conventional and organic cultures. The maximum daily nitrate intake calculated from the consumption of the vegetables under study, represented about 8.6% of the value for the ADI established.

ASSUNTO(S)

hidroponia nitratos hortaliças nitrates hidroponia hortaliças

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