The Soil Environment

Soil is a structured environment that “holds” a wealth of organisms with diverse activities and functions. This chapter examines how soil presents a dynamic and varied habitat, enabling the microorganisms present to interact with each other and with plants, animals, and the soil itself. It highlights that variation in soil properties operates at an impressive range of scales. One gram of soil consists of inorganic and organic fractions. The inorganic particles of soil are classified into three major groups according to their size: sand, silt, and clay. Soil water passes rapidly through wider pores by means of gravity mass flow and diffusion than through narrow pores. The spatial heterogeneity of soils in terms of structure, reducing power, and availability of electron acceptors means that redox chemistry is highly heterogeneous, demonstrating strong spatial and temporal variability. Soil pH is a determinant of soil microbial distribution and activity.