What are the factors affecting the radiation level in soil ?

Soil is formed from the erosion and ablation of rock. The speed of soil formation varies with different rock types (and the weathering processes). Therefore, the composition of natural radionuclides in soil differs in accordance with the rock type they originated from. The amount of natural radionuclides in soil and their radiation levels depend on the geologic origin, geographic location, hydrologic and climatic conditions of the soil.