2. Soils All terrestrial life is ultimately a product of the soil in which primary producers grow.All terrestrial life is ultimately a product of the soil in which primary producers grow. Soil is the source of much of the water and nutrients contained in primary producers, which are then passed along the food chain to consumers.Soil is the source of much of the water and nutrients contained in primary producers, which are then passed along the food chain to consumers. Soils are derived from the weathering of rocks- the parent material.Soils are derived from the weathering of rocks- the parent material.

3. Soil Nutrients Soil nutrients are those essential chemicals necessary for plant growth. They consist of: Macronutrients- nutrients required in large quantities: K, Mg, Ca, N, P, S. Micronutrients- nutrients required in small quantities: Fe, Mn, Zn, Cu, Cl, Bo, Md, Na.

4. Functions of Nutrients Serve as catalysts for chemical reactions. Serve to transport electrons in metabolic reactions. Example: Fe ++ in electron transport system. Serve as structural components of molecules. Example: Ca ++ in cell wall. Influence the permeability of cell membranes. Example: Ca ++ in cell walls.

5. Physical Properties of Soils The properties of soils are inherited mostly from the properties of the inorganic parent material (lower portions of photo). In time, organic matter from the decay of plants is mixed with the soil to improve the soil’s properties (note the darker soil region just below plant growth).

6. Soil Texture Texture depends on particle size: –Coarse sand, >200 microns. –Sand- 20-200 microns. –Silt- 2-20 microns. –Clay- <2 microns. Soils with differing textures have differing physical and chemical properties, and thus influence the growth of plants.

7. Cation Exchange Cations- positively charged chemicals, such as K +, Ca ++, Na +.Cations- positively charged chemicals, such as K +, Ca ++, Na +. Cation exchange capacity- refers to a soil’s ability to hold and give up nutrients.Cation exchange capacity- refers to a soil’s ability to hold and give up nutrients. Silts and especially clays are higher in cation exchange capacity, whereas sands are poor at holding nutrients.Silts and especially clays are higher in cation exchange capacity, whereas sands are poor at holding nutrients.

8. Soil Water Pores- the spaces in the soil between particles. Soil with large pores, such as dune sands (upper photo), drain of water rapidly and are prone to dryness. Soils with small pores like the clays of floodplains (lower photo) hold water tightly and tend to be waterlogged. They may hold water so tightly that not all of it is available to plants. Field capacity- the amount of water that a soil can retain against the action of gravity. Wilting point- When too little water is held in the soil, plants can’t obtain enough to offset the effects of evaporation. This is the point at which leaves wilt.