Rainfall is the greatest influence on soil formation.
Explanation;
Soil formation results from weathering of rocks or materials deposited by erosion from rivers and wind.
Soil differs from one place to another due to the influence by factors such as climate, topography, organisms etc.
The influence from climate is due to temperature and rainfall. High temperatures and rainfall increase the degree of weathering and thus the extent of soil formation.
Among the factors influencing soil formation climate has the greatest influence.