Nitrous oxide emission and denitrification nitrogen losses from soils treated with isobutylenediurea and urea plus dicyandiamide

The aim of this study was to quantify the effects of two N compounds common ly used in controlled release fertiliser (CRF) and bio-inhibitor-amendment fertiliser formulations on denitrification N losses and N2O emission from s everal soil types at different soil moisture levels. The compounds tested w ere the slightly soluble isobutylenediurea (IBDU), and urea mixed with the nitrification inhibitor, dicyandiamide (DCD). Unfertilised soils and soils treated with urea alone served as controls. A significant variation in N2O emission and denitrification rates was observed between the fertiliser trea tments. This variation was found to be attributable to the nature of the ch emical compounds and not to changes in NH4+ or NO3- concentrations. The dim inished denitrification rate over time for all the fertiliser treatments wa s probably associated with the decay of denitrifying microbes. NO emission could generally be correlated with the denitrification rate and the contrib ution of nitrification was estimated to be low. The addition of the nitrifi cation inhibitor DCD to the urea showed no appreciable effect on denitrific ation compared with urea alone but did affect N2O emission. Generally, the IBDU treatment gave rise to the greatest denitrification N loss, while loss es due to N2O emission were lower than control values in many of the trials . The ratio denitrification loss:N2O emission increased with the soil moist ure and clay content of each type of soil, and generally, this ratio was hi ghest for soils treated with IBDU. The soil property that most strongly inf luenced denitrification and N2O emission was water-filled pore space.