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 1. influence of fertilizer splitting on soil and fertilizer nitrogen

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

Soil Science 130(2): 88-99


ISSN/ISBN: 0038-075X
Accession: 005448943

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Two splitting schedules of a 100 kg/ha N dressing applied to winter wheat as Na15NO3 and (15NH4)2SO4 were compared in a microplot study through a four-course rotation (winter wheat, oats, fodder maize, fodder maize) for their influence on soil and fertilizer N. The soil was a well-drained silt-loam containing 0.25% CaCO3 by weight. The treatments investigated are referred to as 3-split (NO3), 2-split (NO3), 3-split (NH4) and 2-split (NH4). The percentage uptake of the fertilizer N by the winter wheat is markedly related to the splitting schedule and, to a lesser extent, to the kind of carrier. The 3-split (NH4) treatment leads to a significant 25% increase in soil N uptake as compared with the O-N reference microplots; the priming effect calculated for this dressing amounts roughly to 12 kg N/ha. The evolution of the residual fertilizer N in the 0-70 cm soil profile shows higher half-life values for the 2-split than for the 3-split applications, i.e., 10.0 vs. 5.1 yr and 13.4 vs. 10.9 yr for the NO3 and the NH4 carriers, respectively. A tentative evaluation of the denitrification and of the NH3-N volatilization losses related to each split, and of the residual fertilizer N left beyond the 70 cm depth has been made. This approach is based on the evolution of the soil conditions (actual water deficit, drainage, temperature) during the 1st cropping season and on the regression curves of the residual first year fertilizer N during the last 3 yr of the crop rotation. The NH3-N volatilization loss represents 5% of the surface-applied ammonium sulfate. Residual fertilizer N beyond 70 cm does not exceed 2% of the applied N dressing. The percentage of N in the crop derived from fertilizer (NDFF) is related to the splitting schedule. Significantly higher NDFF values have been found for the 3-split dressings. Higher values have been calculated for the grain than for the straw. This is true for the fertilizer N taken up by the wheat crop and for the residual N taken up by the oat the 2nd year of the crop rotation.