|Hoeft, Robert - UNIVERSITY OF ILLINOIS|
|Mulvaney, Richard - UNIVERSITY OF ILLINOIS|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 15, 2004
Publication Date: June 17, 2005
Citation: Stevens, W.B., Hoeft, R.G., Mulvaney, R.L. 2005. Fate of nitrogen-15 in a long-term nitrogen rate study: I. interactions with soil nitrogen. Agronomy Journal. 97(4):1037-1045. Interpretive Summary: Results show that overapplication of fertilizer N on a consistent, long-term basis may lead to an accumulation of readily mineralizable soil organic N compounds in continuous corn production systems. After one growing season, profile concentrations of total mineral N were consistently greater with the two highest treatment levels than in the profiles of the lower treatments. The amount of fertilizer-derived mineral N in the profile also increased significantly with increasing N application rate, but more than twice as much soil-derived mineral N was present in the profile at N application rates in excess of the optimum than when N was applied at or below this level. These data suggest that mineralization of residual organic N is promoted when N fertilizer application rates consistently exceed the optimum N application rate on a long-term basis.
Technical Abstract: 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 non-available soil forms. Nitrogen-15-labeled ammonium nitrate (15NH415NO3) 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 non-available 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 offseason 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 non-available N forms, most likely as a result of increased mineralization of crop residues and recently-formed soil organic N.