70291 Nitrogen Loss Potential by Nitrification/Denitrification As Affected by N-Source in Rice.

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Monday, February 6, 2012: 9:00 AM
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Paxton W. Fitts1, Timothy W. Walker1, Jennifer L. Corbin2, L. Krutz3, Bobby Golden2 and Jac Varco4, (1)Mississippi State University, Stoneville, MS
(2)Mississippi State University, Delta Research and Extension Center, Stoneville, MS
(3)USDA-ARS, Stoneville, MS
(4)Mississippi State University, Mississippi State, MS
Nitrification and subsequent denitrification loss of applied N in rice production have been studied minimally. Hypothetically, this loss mechanism could greatly reduce agronomic N use efficiency. Laboratory incubations were conducted to quantify the nitrification potential of a Sharkey clay soil. Within 2 d of incubation, 37% of the recovered N was in the NO3- form and increased to 79 and 93% for 9 and 15 d, respectively. Based on these findings, a field study was conducted in 2011 to evaluate the effectiveness of two nitrification inhibitors (NI), nitrapyrin and dicyandiamide (DCD). Furthermore, a sulfur-polymer coated urea product was also evaluated. Nitrapyrin was applied at 0.5, 1.0, and 1.5 kg ha-1, whereas DCD was applied at 5, 10, and 15% (N basis). Both were delivered with urea liquor applied at 84 and 168 kg N ha-1 14 days before permanent flood establishment (dbf). The controls included N applied at the same rates without nitrapyrin and DCD 14 dbf, as well as 1 dbf. DCD applied at a minimum of 12.5 kg ha-1 resulted in grain yields being 12% greater than the urea alone applied 14 dbf. Increasing the DCD rate to 19 kg ha-1 resulted in a 16% yield advantage. However, all DCD applications resulted in yields less than the standard 1 dbf application. Nitrapyrin applied with 84 kg N ha-1 resulted in 12 and 10% greater yields for 1.0 and 1.5 kg nitrapyrin ha-1, respectively, compared to urea without nitrapyrin. Yield reductions were observed relative to the 1 dbf application. The sulfur-polymer coated urea proved to be the best at stabilizing urea from nitrification loss; however, at both 84 and 168 kg N ha-1, a 5% yield loss still occurred relative to the 1 dbf application. Research is on-going to address nitrification/denitrification loss in rice production.