Nitrate content is an important quality characteristic of vegetables. Vegetable nitrate content is of interest to governments and regulators owing to the possible implications for health and to check that controls on the content are effective. Nitrate itself is relatively non-toxic but its metabolites may produce a number of health effects. Until recently nitrate was perceived as a purely harmful dietary component which causes infantile methaemoglobinaemia, carcinogenesis and possibly even teratogenesis. Recent research studies suggest that nitrate is actually a key part of our bodies' defences against gastroenteritis. In this review are reported: (1) vegetable classification as a function of nitrate accumulation; (2) vegetable contribution to the total dietary exposure of nitrate; (3) European Commission Regulation No. 563/2002 which sets limits for nitrate in lettuce and spinach; (4) the maximum levels set in some countries for beetroot, cabbage, carrot, celery, endive, Lamb's lettuce, potato, radish and rocket; (5) the results of surveys on the nitrate content of vegetables in Italy and other European countries.

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Superabsorbent hydrogels are a particular class of gels, obtained by chemical stabilization of hydrophilic polymers in a tridimensional network. Hydrogels have been widely proposed over the last 40 years for agricultural use with the aim to ameliorate water availability for plants, by increasing water holding properties of growing media (soils or soilless substrates). Most of the traditional hydrogels on the market are acrylate-based products, thus not biodegradable. Due to the increasing attention for environmental protection issues, biodegradable hydrogels arise lively interest for potential commercial application in agriculture. In this study, we evaluated a novel class of cellulose-based superabsorbent hydrogels, totally biodegradable and biocompatible, for agricultural use. The objectives of the tests carried out were: 1) to verify the ability of the hydrogel to modify the water retention properties of the growing media (soils and soilless substrates); 2) to study the effects on the growth of plants grown on media amended with the hydrogel. Water retention curve of a sandy soil amended with 0, 0.5, 1.0 and 2.0% (w/w) of hydrogel was determined using a Richard's pressure plate apparatus. The hydrogel modified the soil water retention properties. The soil moisture at field capacity increased with the highest hydrogel percentage up to 400% compared to the not amended soil, and at wilting point (-15 bar) was similar to that at field capacity of the not amended soil. When added to perlite, a low water holding capacity soilless substrate, 1 or 2% (w/w) of hydrogel increased the container capacity of 28 and 48%, respectively, with no decrease of air capacity. Tests revealed absence of phytotoxicity of the hydrogel, and cultivation trials on cucumber (on soil) and sweet basil (in soilless conditions) showed a general overall enhancement of plant growth and quality when hydrogel was added to growing media. The tested hydrogel showed to be suitable for potential use in agriculture. Its employment should be further evaluated under a cost-effective perspective.

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