The Effects of Mineral Nitrogen on the Fixation of Atmospheric Nitrogen by Vicia Faba L

From 1964 to 1966 a systematic research vas carried out at the Central Research Institute for Plant Production in Prague - Ruzyně, aimed at examining the effect of gradually increased levels of nitrogen and various forms of nitrogen in nitrogen fertilizers on the yield, nitrogen content and the nodulation of the roots of horse bean (Vicia faba LQ. By means of 15N, the proportion of the total nitrogen content of the plant derived from the fertilizer as well as the total utilization of the nitrogen fertilizer by the plant were determined. The experiments were carried out in a series of greenhouse pot tests using a brown soil type, with ammonium sulphate and potassium nitrate as the nitrogen sources. Gradually-increased-levels of nitrogen in ammonium sulphate (0, 5.2, 26.2, 52.5 and 105.0 mgN/kg of soil) applied to the horse bean did not exert any substantial effect on the yield of fresh aerial parts of the horse bean, when harvested at the flowering period. The nitrogen content of tissues of the fertilized plants differed from the control plants (without nitrogen addition) only at the highest nitrogen level (2.7% compared to 3.4% N). The proportion of nitrogen absorbed from the nitrogen fertilizer by whole plant, increased almost as a linear function of nitrogen supplied. Thus the whole plant consumed 51 to 57% of the nitrogen from the first two fertilizer levels, and 64 to 69% from the last two levels of fertilizer, the 52.5-mg and 105-mg levels. In comparing nitrogen supplied as potassium nitrate with nitrogen in ammonium sulphate, at a level of 26.2 mg N/kg of soil, no difference of yield and of percentage nitrogen content in the aerial part of horse bean was found between the plants grown with the nitrogen fertilizers and control plants. The isotopical analysis of nitrogen showed that in the aerial part of horse bean plant the percentage proportion of nitrogen deriving from the fertilizer was higher when potassium nitrate was used (10.8%), than in case of ammonium sulphate application (8.1%). It was found that 54% of the ammonium sulphate and 71% of the potassium nitrate was utilized by the plant. The greenhouse pot tests showed that the nitrogen fertilizer used did not exert any substantial effect on the yield of the aerial portions of the horse bean plant. On the other hand, gradually increased nitrogen fertilizer levels produced in the plant a higher proportion of the plant nitrogen content originating from the fertilizer. Thus, the proportion of the nitrogen fixed from the atmosphere was decreased, which was in good accord with the observation of a reduced number of nodules on the root of horse bean plant. (author)