How does soil fertility differ between Scandinavia and Russia
I don't know much about Scandinavia in the 1500's, and in particular, how much was forested. However, one can say that the whole area was previously glaciated, with much of the topsoil being eroded away by ice, so soils generally tend to be thin, immature, sandy and nutrient poor. We do know that conifers predominated, leaving a soil-litter of pine needles. This latter has a high cation exchange capacity that leads to acid flushes whenever it rains after a long dry period. This acidity tends to leach out nutrients and adds small concentrations of toxic metals. These conditions do not help the soil's fertility. In addition, the valley floors often accumulate peat, hence high organic carbon and acidity. 
The geology of Scandinavia is complex, and difficult to generalize. Periglacial outwash in Sweden and Denmark would have given rise to some fertile areas, especially where there is limestone to counteract the tendency to acidity. So compared to Russia, Scandinavian soil and agricultural potential is more variable.
As regards climate, coastal Norway is much warmer than either eastern Scandinavia and Russia on account of proximity to the Gulf Stream Drift. It also has higher rainfall, so the effective growing season is longer. Northern Scandinavia and Russia have close to 24 hours sunlight per day in high summer, so one wonders whether two growing seasons per year for some crops might be feasible? Are there any agronomists out there who can advise on this question?