Monday, November 5, 2007

Influence of Soil-Urea Ratios on N2O Emissions and Nitrite Accumulation in a Calcareous Silt Loam Soil.

Dongli Liang, College of Resources and Environment, Northwest A & F University, Yangling, China, Richard Engel, Montana State University, Land Res & Env Sci MT State Univ, 334 Leon JohnsonHall PO:173120, Bozeman, MT 59717-3120, and Rosie Wallander, Land Resources and Environmental Sci, Montana State University, Bozeman, MT 59717-3120.

Nest placements of fertilizer are frequently used in developing countries for the production of some crops. Previous research has indicated that placement of urea prills into concentrated zones (e.g. nests) may enhance N2O emissions over more diffuse applications (e.g. broadcast). Two studies were established to better understand this effect. In Experiment I, urea prills (1.3 g) were added to PVC pots containing 6.3 kg Amsterdam silt loam (pH 7.8) soil in a single (SN), double (DN), and triple (TN) nest arrangements, plus a broadcast placement to create a gradient of decreasing fertilizer to soil dilutions. In Experiment II, urea prills were added to jars (930 ml) containing 500 g Amsterdam soil at six rates (0, 46, 92, 184, 368, 736, ug N g-1). Maximum N2O fluxes were similar for the three nests and broadcast in Experiment I, but cumulative emissions were enhanced as the ratio of fertilizer to soil in the nest became more concentrated. Over the 46 d experiment period cumulative emissions were equivalent to 45.2, 36.5, 25.0, and 17.5 mg N2O-N m-1 for the SN, DN, TN, and broadcast treatments, respectively. In Experiment II, cumulative N2O emissions increased with urea N rates as anticipated and were highly correlated (r=0.756) with soil nitrite concentrations. Small amounts of nitrite were present in the soil up to 6 d following fertilization in the 46, 92, 184, 368 ug N g-1 treatments. For the 736 ug N g-1 rate, appreciable nitrite (15-206 ug NO2-N g soil) was present over the entire 21 d incubation period. The results of this study indicate applying a high urea rate to a small soil volume, i.e. nest, may lead to inhibition of nitrite oxidizers. Under these conditions N2O emissions and fraction of applied fertilizer N lost as N2O are enhanced over diffuse urea applications.