Simulation of Soil Processes in Northern Climates with the STICS Crop Model.

Microbial communities in agricultural soils remain active during the non-growing season in northern countries, even though soil temperatures may stay below 0°C for weeks to months. As a result, nitrogen (N) losses through leaching and gaseous emissions during winter can be a substantial proportion of total annual N losses (up to 60%). However, most soil-crop models do not adequately account for the effects of winter conditions on soil N cycling in regions where soil freezing and frequent snowfall occur. Previous work has shown that predictions of soil temperature and moisture under snow cover can be significantly improved by using a simple snow cover model to pre-process climate data before running the STICS soil-crop model. However, even accurate prediction of snow cover, soil temperature and soil moisture might not be sufficient to adequately simulate more complex soil processes in winter, such as drainage, nitrification, denitrification or mineralization.

The objective of the present study was to evaluate and improve the performance of STICS, coupled with a previously developed snow-cover model, in simulating soil N processes in eastern Canadian agricultural fields during winter. Several experimental datasets from Fredericton (New-Brunswick, Canada), Quebec (Quebec, Canada) and Ottawa (Ontario, Canada) were used to evaluate the model performance in simulating the temporal dynamics of drainage, soil nitrate and ammonium, and N₂O emissions during the non-growing season (late fall to end of spring thaw). Preliminary results indicated that the use of the snow-cover model significantly improved the prediction of drainage from winter through the end of spring thaw and snowmelt. For soil N processes, initial results showed that the model’s thresholds controlling the lower temperature limit of nitrification, denitrification and mineralization are too high, leading to an underestimation of these processes when soil temperature is close to or slightly below 0°C. Further work will focus on determining appropriate temperature thresholds.