What is the northern european plain's excellent soil is called?

Northern European Plain's excellent soil is called loess.

The European continent has varying deposits of loess soil from few decimeters to thick tens of meters. The Northern European countries whose soil predominantly loess are France, Poland, Germany, and northern Ukraine.  

The soil in this area is due to periglacial conditions. Loess results from built-up of wind-blown dust/silt that forms sedimentation. The silt particle is normally 20-50 micrometer in size that consists of less clay and a balanced quantity of sand and silt. It is homogenous soil which is also porous.