Monitoring of gaseous nitrogen losses from nitrogen fertilizers in model experiments

Gaseous nitrogen (N) losses were studied from N fertilizers applied to winter wheat under field conditions and in large pots in the open section of a greenhouse. The same soil type was used. Ammonium nitrate (NH4NO3), urea [CO(NH2)2], and ammonium sulphate [(NH4)2SO4] distributed at the beginning of tillering were tested in a microplot experiment (16 g N m-2). Ammonium nitrate applied at different doses in the period between the beginning of tillering and that of flowering was tested in pots filled with 70 kg soil (2 g N pot-1). The pots were watered. Gas traps of 4.4 dm3 and 1.8 d,3 were laid between the rows of the microplots and into the pots, respectively. Ammonia (NH3), nitric oxide (NO), nitrous oxide (NO2), dinitrogen oxide (N2O), and nitrogen (N2) contents of trapped soil air were analyzed by gas chromatography during vegetation. Nitrogen fertilizer application significantly increased the amount of nitrogenous gases in the trapped soil air and CO(NH2)2 application resulted in the highest nitrogenous gas concentration. The N losses measured at the different samplings were not higher than 1.2% and 2.7% of the N doses applied in the field and pot experiment, respectively. The complete transformation of the fertilizers took place practically within 11 and six weeks after their distribution to wheat grown in the field and in the pots, respectively. The composition of the nitrogenous gases changed during vegetation depending on the applied fertilizer N form. The proportion of the "greenhouse gas", N2O increased within the total amount of nitrogenous gases in the field traps with all fertilizer N forms. It decreased, however, in the traps of the pots, where the soil had a higher moisture level. Among the nitrogenous gases tested, N2 showed by far the highest and NO the lowest concentration in both experiments.