AP Environmental Science Chapter 14, Food and Soil Resources Living in the Environment, 14th edition, G. Tyler Miller

Definition of SoilThe outermost solid layer of the EarthA natural product formed from weathered rock by the action of climate & living organismsA collection of natural bodies of earth that is composed of mineral & organic matter, & is capable of supporting plant growthSoil FormationVideo: Soil FormationSoil formation - Parent material is slowly broken down by biological, chemical and physical weathering. Biological - Respiration of plant roots and other organisms produce CO2, which reacts with soil water to produce carbonic acid (H2CO3). Chemical - Acids crack rocks water seeps in breaks down particles.Physical - Weathering introduces water that breaks down particles.Time scale - Formation of 2.5 cm of topsoil takes 200 - 1000 yrs. Soil Formation

3Soil FormationComplex mixture of organic and inorganic components

Parent material = starting material that affects the composition of the resulting soilWeathering = the processes that break down rocks and minerals (1st step in soil formation)Erosion = the movement of soil from one area to another 38% of Earths surface has been converted for agriculturecultivating soil, producing crops, and raising livestock for human use and consumption

4Soil Composition Soil Composition45% Mineral particles (broken down pieces of rock)5% Organic matter (humus - from dead organisms, worm castings, leaf litter)25% Water (precipitation)25% Air (More with sandy soil, less with clay soil)Soil organisms - Millions in one teaspoon of fertile agricultural soil!- bacteria, fungi, algae, microscopic worms. provide ecological services such as worm castings, decomposition to humus, breaking down of toxic materials, cleansing water, nutrient cycling from decomposers or upon death

5

Soil Composition

7Soil Texture

determined by the proportion of particle size classestexture is partly inherited from parent material and partly a result of the soil forming processparticle classification:rock fragments (> 2.0mm diameter)sand (0.05-2.0mm)silt (0.002-0.05mm)clay (