Monday, November 13, 2006
47-6
Effect of Urea-nitrogen Fertilizer Placement on N2O Emissions From a Silt Loam Soil.
Ashley Bembenek, Matt Dusenbury, and Richard Engel. Montana State Univ, Dept. of Land Resources and Environmental Sciences, Bozeman, MT 59717-3120
Agricultural use of fertilizer N is a major component to anthropogenic releases of nitrous oxide (N2O) into the atmosphere. Emission levels of N2O from fertilizer may be influenced by placement techniques. The objective of this study was to investigate this phenomenon for urea-N. A greenhouse study was conducted using PVC pots (19.5 cm diameter x 35 cm height) filled with an Amsterdam silt loam soil (Typic Haplustolls). Four urea-N placement techniques including broadcast surface, broadcast incorporated, subsurface band and nest were compared plus KNO3 and unfertilized controls. Gas samples were collected approximately daily for 68 d by placing vented covers on the PVC pots. Aliquots (25 ml) were withdrawn after 30 min and analyzed for N2O on a gas chromatograph equipped with an ECD. Soil emissions of N2O were enhanced with all urea-N applications. Nitrous oxide emission-time profiles were affected by urea placement (P<0.10) with the highest overall losses occurring in the nest and subsurface band applications. Distinct activity peaks, equivalent to 114 and 93 µg N2O-N m-2 hr--1, occurred 25 and 12 d following fertilization for nest and subsurface band applications, respectively. Emission-time profiles for the broadcast surface and incorporated urea did not exhibit distinct peaks. Nitrous oxide emissions from KNO3 were low and only slightly higher than the unfertilized control, indicating nitrification was the primary process responsible for N2O production in this experiment. Fertilizer induced losses of N2O (fertilized treatment – control) were equivalent to 0.28, 0.19, 0.13, 0.11, and 0.03% for the nest, subsurface band, broadcast surface, broadcast incorporated , and KNO3 treatments, respectively. The results of this study demonstrate that placement of urea in localized areas results in higher emissions than diffuse applications.