Probability distribution and spatial dependence of nitrous oxide emission: Temporal change in hummocky terrain

Climate controls soil N2O emissions via its effects on soil properties such as water-filled pore space. Changes in climate should produce changes in the probability distribution and spatial dependency of soil N2O data. Knowing the extent of the changes in the distribution of this data is important for validating model predictions. The objectives of this study were to describe the probability distributions and estimate the spatial dependency of soil N2O emission data. On a hummocky, agricultural landscape in Saskatchewan, N2O emission data and related soil variables were taken from a 128-point transect 15 times over 2 yr. Probability distributions were compared using a Chi-square test. The range in spatial correlation was determined using the indicator semi-variogram with a nested model fit approach. The mean N2O flux ranged from 25.3 to -0.2 ng N2O-N m(-2) s(-1). Probability distributions ranged in shape from reverse J-shape through log normal to symmetrical. The majority of distributions were statistically different from each other, showing a lack of temporal stability. Mean N2O flux and distribution shape followed an event-based/background emission pattern. High flux events had statistically similar, reverse J-shaped distributions. As mean N2O flux decreased to a background level distribution, shape changed to log normal and symmetrical forms. A high nugget/sill ratio characterized the majority of sampling dates, although spatial dependency was generally moderate. flux values in the fourth quartile tended to have a spatial dependency of 15 m, probably reflecting a topographic control at a landform element scale.