The aim of this paper is to summarize current knowledge on nitrogen nutrition of vegetable species, taking into account not only crop requirements, but also the necessity to conservate the environment. After examining the effects of nitrogen deficiency and excess on vegetables, with a particular attention to the qualitative aspect of production, nitrogen uptake by the main crops is reported and the possibility to cope with these demands with the minimum impact on environment is discussed. The efficiency of the main nitrogen sources (mineral fertilizers, organic fertilizers, crop residues and cover crops) and the strategies to optimize their use are considered. First of all, a sustainable vegetable cultivation cannot do without organic sources. Nitrogen coming from crop residues and cover crops may be notable and in some cases it can meet the requirements of the crop that follows. From this comes the opportunity to include in the rotations crops leaving plenty of residues (e.g. cauliflower and broccoli) and cover crops, especially legumes. But, as crop residues and cover crops are mineralized quickly, further fertilizations are necessary to enrich the soil with organic matter, based on manure or compost. These should be planned in the rotation at least once every two years, alternated with cover cropping. Anyway, nitrogen coming from organic sources shows low efficiency and it is not easy to manage, due to the difficult control of its release and, consequently, of its loss by leaching or denitrification. Therefore, with the obvious exception of organic agriculture, synthetic fertilizers are still necessary, although their use surely needs to be rationalized. That may be achieved by controlling and splitting the total amount applied, by localized application, the resort to slow-release fertilizers and fertirrigation. The paper is completed by citing the main CE regulations providing incentives for a rational management of nitrogen in agriculture; finally, the possible use of models is briefly mentioned.
Keywords: vegetable quality, nitrogen requirements, nitrogen sources, fertilization, environment conservation