There are five major soil-forming factors that will influence the characteristics of a soil. The three passive factors are , topography, and . The two active factors are and climate. Usually the most important of these factors is . As a generalization, soil-forming processes are most active when the temperature of the region is (high or low), and the amount of moisture available is (high or low). In terms of topography, soils tend to be deepest where the slope of the land is (steep/gentle).
The solid part of the soil includes both inorganic minerals and matter. In an average soil, almost half the volume may be made up of pore spaces, which contain either or . One of the most important physical properties of a soil is its , which is the relative proportion of sand, silt and clay in the mineral fraction. The largest particles (from 0.05 to 2 mm) are . The smallest particles (below 0.002 mm) are . The intermediate sized particles are silt. The particles are chemically active in the soil. A soil which is a good mixture of all three particle sizes, in which no one of the separates is dominant, is called a . A soil with a high proportion of will have good drainage and good aeration. A soil with a high proportion of will usually hold more water at field capacity.
water is water that is in the soil temporarily, infiltrating after a rain, then draining away. Water which remains in small pores in the soil, and on the surfaces of soil particles, is called water. Water which adheres tightly in a microscopically thin film around soil particles is called water. water is the type of soil water that is most available to plants.