Author
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Phillips, Beckie |
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Submitted to: Trade Journal Publication
Publication Type: Trade Journal Publication Acceptance Date: 1/1/2007 Publication Date: 2/1/2007 Citation: Phillips, R.L. Late-Autumn Manure Application Increases Greenhouse Gas Emissions from Frozen Croplands. Trade Journal Publication. Crop Science of America News 52:4. Interpretive Summary: Technical Abstract: Organic foods are grown in over ½ million hectares of U.S. cropland, and the question of how organic fertilizer amendments influence trace gas fluxes may vary among production regions and with type, timing, and rate of amendment application. Intensive studies of nitrous oxide fluxes indicate highly variable but significant responses to soil amendments such as several synthetic fertilizers, composts, and fresh animal manures. The question, however, of how gas fluxes are affected by certified, dehydrated manure in an organic production environment has not been explored. We chose to consider this issue in the context of a large-scale, on-farm approach so that soil, weather, and tillage conditions would be in alignment with a production environment. Organic soil amendments are typically applied in the autumn just prior to freeze-up, while conventional fertilizers are typically applied in the spring following soil thaw. To address the question of how organic amendments alter nitrous oxide fluxes following autumn application, two 80-acre fields in production were selected: one managed conventionally >50 yrs and one managed organically >5 yrs. The conventional field had not been fertilized for 1.5 yrs, while the organic field was amended with 67.5 kg N/ha of dehydrated manure 17 days prior to the experiment. Both soils share similar soil properties, climate, and crop rotations and were located <1 km from each other in Georgetown, Minnesota. Soil temperatures below freezing were recorded one week following amendment application and soil cores (0-15 cm depth) collected ten days later. Intact core temperatures remained near field conditions (-2° to -3° C) for the duration of the laboratory experiment. Incubations at -2° C indicated nitrous oxide fluxes from the organically amended soil were 10.4 g /ha/d, and 3.3 g/ha/d for the unfertilized soil. Denitrification rates were measured on the same soil cores at -2° C using the acetylene inhibition technique. Organic soil N2O+N2 emissions increased 51% to 15.7 g/ha/d compared with 16% for the unfertilized soil (3.8 g/ha/d). Results indicate that denitrification is active below freezing and that addition of dehydrated compost increased denitrification, compared to the unfertilized soil. If these rates are representative of winter N losses during a typical winter, then ~2.4 kg denitrified N ha-1 may be emitted from organically-amended, frozen soil (3.6% of total N applied), compared to ~0.6 kg for the unfertilized, frozen soil. |
