Abstract
The use of nitrogen fertilizers is one of the main effects for the accumulation of nitrates in plants. Conventional agriculture, in comparison to integrated and organic farming, causes greater environmental pollution and poorer quality of crops. Within the framework of the research, we studied the influence of the method of cultivation on the content of nitrates in the samples of lettuce (Lactuca sativa L.). The samples were received directly from growing areas from different parts of Slovenia and analysed in the laboratory for the nitrate content (NO3-) according to the accredited method. The samples from conventional cultivation showed the highest sample representation (51 %), with values in the highest concentration range (1000 - 2500 mg of NO3- kg-1, one sample exceeded 2500 mg kg-1 fresh mass). Within the framework of integrated cultivation, there were less such samples (34 %), and among the samples from organic cultivation no sample exceeded 1000 mg of NO3- kg-1. Of 88 analysed samples, one sample exceeded the statutory limit value applicable to lettuce of the type Iceberg ('Ljubljanska ledenka'). On average, the Iceberg samples contained more nitrates than other types of lettuce.
Highlights
Nitrogen is the most important element in plant nutrition
The Commission Regulation (EU) No 1258/2011 defines the maximum permissible levels of nitrate for the lettuce cultivar groups (Lactuca sativa L.) and among this groups separately defines the permissible value for Iceberg type lettuce, which naturally accumulates less nitrates
In the light of the above classification, we present the values of nitrates in analyzed samples of lettuce (Table 2 and 3)
Summary
Nitrogen is the most important element in plant nutrition. The plants need it as a nutrient for building amino acids, proteins, nucleic acids and other vital compounds. The plants receive the nitrogen in the form of nitrate (NO3-) and ammonium ion (NH4+). Due to the oxidation of the ammonium nitrogen form to nitrate, which takes place in the soil in the presence of bacteria, the nitrate is the predominant form received by the plant (Below, 1994). The intensity of farming and the associated use of nitrogen fertilizers cause nitrates to accumulate in plants. Most of nitrate is accumulated in vegetables (especially leafy vegetables), less in field crops, and much less in fruits (Schuddeboom, 1993; Ysart et al, 1999; Zhong et al, 2002). Nitrate itselves is harmless to health, after ingestion, it is influenced by microbiological processes
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