Effect of different forms of farm dairy effluent, with and without animal urine, on nitrification, denitrification and N₂O emissions : A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Agricultural Science at Lincoln University

Nitrous oxide (N₂O) is one of the most important greenhouse gases. Agricultural soils are the largest source of N₂O emissions. In New Zealand, the application of farm dairy effluent (FDE) on pasture soils is the third largest source of N₂O emissions from grazed grassland. Recently, new FDE treatment technologies have been developed to separate out solids from liquids to produce treated clear water and treated effluent, aimed at recycling water, increasing the storage pond capacity and minimising contamination of waterways. However, it is not known how the treated clear water and treated effluent would affect the N₂O emission factors compared with the standard untreated effluent, and whether the treated effluent would interact with animal urine to result in different N₂O emission factors for the animal urine-N. Thus, the objectives of this research were: a) to determine N₂O emissions from treated effluents (including treated effluent and treated clear water) compared with standard FDE applied to soil; b) to determine N₂O emissions from treated FDE and standard FDE co-applied with animal urine; c) to determine ammonia oxidising bacteria (AOB), ammonia oxidising archaea (AOA), denitrying microbial functional genes, and mineral N dynamics following the application of treated FDE and, standard FDE with or without urine; and d) to determine the relationships between N₂O emissions and the FDE properties.Two incubation experiments were conducted to measure N₂O emissions, mineral N dynamics, soil pH and the abundance of AOB, AOA, and denitrifying functional genes (nirS, nirK and nosZ)