A series of field and laboratory experiments were undertaken to examine the effects of incorporation of plant material on emissions of N<SUB>2</SUB>O from agricultural soils. The overall aim was to increase understanding of that part of the agricultural N cycle, associated with the release of N after incorporation of crop residues and green manures into soil, and subsequent N<SUB>2</SUB>O emissions to the atmosphere. N<SUB>2</SUB>O emissions from growing corps and following addition of various residues and green manures to soil were measured and compared. The effects of crop type, fertiliser application, cultivation techniques, soil type, and climatic conditions, and also of the addition of high C substrate in the form of paper waste, on these emissions were investigated. Emissions of N<SUB>2</SUB>O were increased after cultivation of soil, attributed to increased accessibility of organic matters to soil microbes, and improved gaseous diffusion. Emissions were higher following incorporation of plant material than emissions from bare soil. Generally, fluxes were increased within a few hours or days after cultivation and/or incorporation, but the effect was short-lived. Most of the N<SUB>2</SUB>O was emitted during the first 2 weeks. The magnitude and timing of N<SUB>2</SUB>O released within this period was highly dependent on temperature and rainfall following incorporation, and the cultivation technique employed. The C:N ratio of the incorporated plant material had a considerable effect on rates of decomposition, and on subsequent N<SUB>2</SUB>O production during nitrification and denitrification. Higher emissions were typically measured after incorporation of material with a low C:N ratio, such as legumes, than when material with higher ratios, such as cereal straw, was involved. When material with a high C:N ratio was added, N was immobilised. Nevertheless, the presence of high C:N paper waste increased N<SUB>2</SUB>O emissions from incorporated vegetable crop residues. This was attributed to the creation of more anaerobic sites in the soil. Emissions of N<SUB>2</SUB>O increased within a few days of applying mineral N fertiliser to spring-sown cereal crops. Again, these fluxes were short-lived. Use of <SUP>15</SUP>N-labelling in this experiment showed that approximately 50% of crop N at harvest was derived from applied fertiliser. In other experiments, the presence of a growing crop particularly a legume, increased emissions, compared with those measured from bare soil. The measurements of soil mineral N (the substrate for N<SUB>2</SUB>O) were compared with the amounts predicted by various N models. Practical suggestions were made for ways to lower N<SUB>2</SUB>O emissions from agricultural systems, thereby reducing detrimental effects on the ozone layer and global warming.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:641190 |
| Date | January 1997 |
| Creators | Baggs, Elizabeth Mary |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/26183 |
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