QUANTIFYING DENITRIFICATION ON A FIELD SCALE IN HUMMOCKY TERRAIN

In this study a landscape classification and daily climatic data were used to extrapolate from a number of discrete denitrification rate measurements to an annual field average. Denitrification rates were calculated from modelled daily moisture contents and observed daily temperature using regression equations. Different regression equations were used for crop and fallowed fields, and for three distinct landscape groups; depositional, intermediate, and erosional. Good correlations were found between predicted and measured denitrification rates. Annual denitrification losses were greatest under fallow, ranging from 50.5 kg N ha-1 on the low level landscape element to 3.1 kg N ha-1 on the diverging blackslope. Losses from cropped soil ranged from 12.8 kg N ha-1 on the diverging footslope in 1988 to 0.7 kg N ha-1 on the diverging backslope in 1986. Field average denitrification losses were estimated to be 3 kg N ha-1 in 1986 (wheat), 16 kg N ha-1 in 1987 (the fallow year) and 4 kg N ha-1 in 1988 (canola).