Fertilizer nitrogen budget of nitrogen 15 labeled sodium nitrate and nitrogen 15 labeled ammonium sulfate split applied to winter wheat in microplots on a loam soil
Riga, A.; Francois, E.; Destain, J.P.; Guiot, J.; Oger, R.
Plant and Soil 106(2): 201-208
Labelled fertilizer N applied to winter wheat as Na15NO3 and (15NH4)2SO4 at a total N dressing of 100 kg ha-1 was used in a microplot balance study to investigate the fate of each split fraction at three growth stages: end of tillering, heading and beginning of flowering. Results indicated that while the percentage utilization of the applied N by the grain and total crop increased considerably from the first to the third split application, these values diminished steadily in the straw. Grain recovery values for the first, second and third split applications were 34.2%, 51.5% and 55.7% for the NO3 and 32.3%, 48.4% and 52.5% for the NH4 carrier, respectively. The corresponding recovery values for the whole plant were 54.6%, 67.8% and 69.9% for the NO3 and 51.7%, 63.5% and 66.1% for the NH4 carrier. A greater proportion of the fertilizer N applied at the end of tillering stage was found in the vegetative plant components as compared with the grain. The reverse occurred for the N applied at the heading and at the beginning of the flowering stages. The residual fertilizer N found in the soil amounted to 18.0%, 10.4% and 11.6% of the applied NO3-N and to 22.5%, 12.7% and 15.2% of the applied NH4-N for the respective split applications. No differences were found for each split application between the two carriers as far as the unaccounted fertilizer N was concerned. The losses were 26.6%, 22.3% and 18.6% of the applied N for the three split applications, respectively. The application of fertilizer N did not lead to any increase in soil N uptake by the crop.