Cover: A view over the integrated field at Logården.

Community ecology of denitrifying bacteria in arable land Denitrifying bacteria comprise a functional guild that under anaerobic conditions is able to use nitrogenous compound for respiration. Agricultural soils are often fertilized with nitrogen, and the reduction of nitrate and nitrite to nitric oxide, nitrous oxide and dinitrogen via the denitrification pathway, leads to gaseous emissions from the nitrogenous compounds, a subject of great environmental and economic concern. This thesis examined denitrifiers, nitrate reducers, ammonia oxidizers and total bacteria, in terms of community structure, abundance and function in different arable soils. Denitrifying bacteria were described using the signature genes that encode the analytic subunits of denitrification enzymes. Appropriate targets and methods for this were evaluated. An assessment was carried out of how these biological factors are affected by different fertilizer and management practices. The spatial distribution of the denitrifying bacteria, and how this was correlated to soi