What is it called, what process, occurs when nitrogen is taken from the atmosphere and brought to the soil.?

The term is nitrogen fixation.  Leguminous plants such as alfalfa, bean plants, and peanut plants contain symbiotic bacteria in their roots which are capable of converting atmospheric nitrogen to nutritive compounds usable by the plant.  This is why fields are often planted with a leguminous plant between growing seasons to restore nutrients to the soil.

The process is called as nitrogen fixation.

The process is called Nitrogen Fixation. It is of two types Symbiotic and non-Symbiotic fixation of atmospheric nitrogen. Nitrogen in the air comes down from the atmosphere with rain, it combines with water molecules when it thunders (which provides high temperature). When it enters the soil, two types of soil bacteria (symbiotic and non-symbiotic) act on this nitrogen compound and turn it from inorganic form to organic form.

nitrogen cycle starts with the fixation of atmospheric nitrogen in the soil either during lightning or due to some symbiotic bacteria that fix nitrogen of the atmosphere into the soil called rhizobium. they are attached to the roots of legumes . after the nitrogen is added to the soil , it is absorbed by plants as a nutrient and performs the photosynthetic activity . these nitrogenous products are eaten by animals and they release this nitrogen during defaecation and again this nitrogen is fixed into the soil from the atmosphere by the bacteria i mentioned about earlier.