Fate of Nitrogen-15 in a Long-Term Nitrogen Rate Study
- W. B. Stevens *a,
- R. G. Hoeftb and
- R. L. Mulvaneyc
A better understanding of how N management practices affect transformations and movement of fertilizer N may lead to more efficient N management. The objectives of this work were to determine how long-term N fertilizer history in a continuous corn (Zea mays L.) production system affects (i) movement of fertilizer N through the soil profile and (ii) cycling of fertilizer N between available and nonavailable soil forms. Nitrogen-15-labeled ammonium nitrate (15NH4 15NO3) was applied at 0, 67, 134, 201, or 268 kg N ha−1 to subplots of long-term N rate plots. Twenty to 55% of labeled N was converted into either organic or clay-fixed forms during the first growing season, with the percentage decreasing with increasing N application rate. Significantly more N was released from nonavailable forms in plots where the historical N application rate had exceeded the long-term optimum (186 kg ha−1) than in plots that received lower rates. Little fertilizer-derived N leached from the profile during the first growing season, but losses did occur during the off-season and subsequent growing season when N application rate was higher than the optimum. It was concluded that a history of excessive N application may decrease response of subsequent crops to fertilizer N due to greater release from nonavailable N forms, most likely as a result of increased mineralization of crop residues and recently formed soil organic N.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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