摘要：Nitrogen, as the most important element of biological construction of plants, can be taken from the atmospheric nitrogen (N2) (N ≡ N) or it can be applied in fertilizers. In the first case the nitrogen is taken without financial costs and without pollution, while in the second case it becomes more and more expensive and very polluting. This work wants to demonstrate that by using biological models, known since long time but uninvestigated and little put into practice, we can substitute, even in the case of wheat, a big quantity of nitrogen, which equals about 4000 kg/ha quality kernels. The model used is given by the non-symbiotic association between wheat and Azospirillum braziliense bacteria. The quantity of fixed nitrogen is correlated to the ecological condition of soil, condition which expresses an optimum biological activity given by the ratio water/air in soil, by its energetic sources, by its physical condition and by crop technologies and can reach 90-100 kg/ha. But it correlates very significantly with the soil moisture, being much reduced both in excess or lack of water in the soil
