Fate of fertilizer nitrogen applied to winter wheat as nitrogen 15 labeled sodium nitrate and nitrogen 15 labeled ammonium sulfate studied in micro plots through a 4 course rotation 2. fixed ammonium turnover and nitrogen reversion

Van-Praag, H.J.; Fischer, V.; Riga, A.

Soil Science 130(2): 100-105


ISSN/ISBN: 0038-075X
Accession: 005448944

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The fate of fertilizer N applied to winter wheat as Na15NO3 and (15NH4)2SO4 according to 2 splitting schedules was followed in a silt-loam for fixed ammonium turnover and N reversion. The experiment was conducted in microplots through a 4-course rotation: winter wheat, oats, fodder maize and fodder maize. The treatments involved in this experiment are referred to as 3-split (NH4), 2-split (NH4) and 2-split (NO3). The residual fixed NH4+-N in the 2-split (NH4) treatment amounts to 7% of the residual fertilizer N left in the 0-20 cm layer after the wheat harvest. This fraction decreases by 55% over the following 3 yr of the crop rotation, which represents a faster release when compared with the decrease of the residual fertilizer N as a whole. The amounts of residual fixed NH4+-N found in the 0-10 cm layer correspond to 0.82 and 0.17% of the applied fertilizer N for the 2-split (NH4) and the 3-split (NH4) dressings, respectively. The influence of the splitting pattern on the fertilizer NH4+-N fixation seems to be related to the method and timing of the NH4+ and K+ fertilizer applications. A redistribution of fertilizer NH4+-N into the lower layers was observed after the harvest of the oat crop. Intensive defixation (24-39%) of native NH4+-N due to the oat crop has been found in the lower layers of the cultural profile with practically no release in the 0-10 and 10-20 cm layers. Release of native fixed NH4+-N seems to be inhibited to a greater extent by the addition of annual K+ dressings than that of recently fixed NH4+-N. The availability ratio established after the first 3 crop harvests for the 2-split (NH4) treatment decreases from 7.83-2.93 and from 12.12-3.62 in the 0-10 and 10-20 cm layers, respectively.