[Nitrates of agricultural origin: their accumulation in plants and their effect on the environment].

When dealing with the environmental impacts of nitrate nitrogen, one must, first, underline the main place of nitrogen in the dietary needs of man. This element is simultaneously one of the main factors of crop yields, and the first step in the elaboration of proteins. The accumulation of nitrates in crops is defined, its draw-backs are briefly reminded. Nitrate content differs between the organs: stems, petioles, young roots are richer than limbs of leaves; fruits are very poor. The factors of nitrate accumulation are reminded: the nitrogen availability in soil, the light, the other nutrients, and the plant characteristics (e.g., age, cultivar). Ways to obtain a better control of nitrate content in edible parts of spinach, carrot and tomato are discussed. Then, the nitrogen cycle in the soil is briefly described. The influence of various agricultural systems (pastures, annual cropping, wheat, corn, soja) on the nitrate content of groundwater is shown.