[Determination of the accumulation of nitrates in plant tissues].

Nitrate accumulation in the plant represents the difference between nitrate absorption and their use. The absorption depends essentially on the available nitrate supply to the plant. We can distinguish two sources of nitric nutrition: mineral nitrogen fertilising of the crop under consideration, and mineralization of the soil organic nitrogen. While the former is directly dependent on us, the latter can hardly be controlled in terms of quantity as well as timing of the supply. On the basis of an example it is shown that the latter source of supply, as compared to mineral nitrogen fertilizing, sometimes leads to an abnormal accumulation of nitrates when the time of supply (mineralization) is not in conformity with the crop requirements during the corresponding period. The use of nitrates obviously depends on the specific physiology and the conditions affecting plant nutrition. We think that nitrate accumulation in the leaves is linked to the relative importance of nitrate metabolism in the roots and in the leaves. The tendency of various plant component to accumulate nitrates is also discussed on the basis of a few examples.