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SOIL The skin of the Earth

10 Reasons we study soil - it’s a(n) 1. Great integrator: all parts of ecosystem 9. Producer and absorber of gases 8. Medium for plant growth 10. Medium of crop production 7. Home to organisms (plants, animals and others) 3. Waste decomposer 2. Snapshot of geologic, climatic, biological, and human history 4. Source material for construction, medicine, art, etc. 5. Filter of water and wastes 6. Essential natural resource

5 Soil Forming Factors 3. Parent Material 1. Topography 5. Time (The first four factors over) 4. Climate 2. Biota These five factors work together to create a unique soil profile made of layers called horizons.

l Soil Texture: m The way the soil “feels” is called the soil texture. m Soil texture depends on the amount of each size of mineral particles in the soil. m Sand, silt, & clay are names that describe the size of individual mineral particles in the soil. èSand are the largest particles and they fell “gritty” è Silt are medium sized, and they feel soft, silky or “floury” è Clay are the smallest sized particles, and they feel “sticky”

Soil Texture: Relative Size Comparison of Soil Particles frisbee Silt (feels floury) dime Clay (feels sticky) beachball Sand (feels gritty) ( mm, USDA) ( mm, ISSS) ( mm, USDA) ( mm, ISSS) (< mm, USDA) (< mm, ISSS)

Soil Texture Triangle

l Soils are more cohesive when they have more fine particles (Clays). l Soils are more loose when the have more coarse particles (Sand). l Different combinations of coarse & fine contents produce different soil textures. l A loam is a mixture of sand, silt & clay: sandy clay loam is best in landscapes. l Many other inclusions, such as cobbles, boulders. Effects of Soil Texture:

Soil Consistency Describes the general organization of the soil. Hold a moist sample between the thumb and forefinger, and gently squeeze it until it falls apart. The soil is classified by the following categories 1. Loose: You have trouble picking out a single sample and the structure falls apart before you handle it. 2. Friable: The sample breaks with a small amount of pressure. 3. Firm: The sample breaks when you apply a good amount of pressure and dents your fingers before it breaks. 4. Extremely Firm: The sample can't be crushed with your fingers (you need a hammer!).

Basic Soil Components Soil Particles: Mineral & Organic Pore Spaces: location of air & water Porosity! Permeability!

O horizon: Is the topmost layer of most soils (100/0) Composed of plant litter at various levels of decomposition & humus. A horizon: Humus & other organic materials are mixed w/mineral particles (75/25) Translocation has removed finer particles & soluble substances, these may be deposited at a lower layer. dark in color & light in texture & porous. B horizon: Mineral soil layer which is strongly influenced by humus deposition (50/50) This layer receives material from the A horizon. Higher bulk density than A horizon due to its enrichment of clay particles. May be colored by oxides of iron & al or by CaCO3 from the A horizon. C horizon: Weathered parent material (25/75) Texture is variable w/particles ranging in size from clay-boulders. It is not influenced by soil formation, translocation, &/or organic modification. R horizon: Bedrock layer in a typical soil profile (0/100) Unweathered bedrock. E horizon: White eluviation layer, wet layer w/mineral leaching jP9Q

If a soil is low in phosphorus (P) or potassium (K), it will tie-up or "fix" much of the applied fertilizer P & K (P 2 O 5 and K 2 O) into forms that are not available to the plants. The soil is a reservoir for the nutrients that have been applied or generated by other means over the years. Fertilizer puts nutrients into one side of a reservoir while the plants are taking them out of another end. What happens inside of this nutrient reservoir is soil chemistry & microbiology. These processes, along with weather, determine how much access the plants have to the nutrients within the reservoir.

1. Compaction 2. Contamination 3. Erosion 4. Salinization 5. Reduction in Productivity 6. pH

Movement of top soil components, from one place to another. Two main agents: 1. flowing water 2. wind Erosion makes soil less fertile & less able to hold water.

Topsoil is eroding faster than it forms in 1/3 of world’s croplands. 85% degradation of human activities as a result of erosion. Area as big as China +India eroded so far!

60% of eroded soil ends up in streams. Lose 7-21% of topsoil each decade (10yrs). Mostly caused by: mismanagement, overgrazing, deforestation and over harvesting. $46 million in damages per hour.

Terracing - keeps water for crops and reduces erosion through runoff. Contour farming - planting crops in rows rather than up and down on hills. Strip cropping - alternating crops in rows to cover soil and avoid erosion. No Till Farming – involves not plowing the land and reducing nutrient loss through erosion.

IPM: an effective and environmentally sensitive approach to pest management that relies on a combination of common-sense practices. Hydroponics: is a method of growing plants using mineral nutrient solutions, in water, without soil. Organic Farming: relies on techniques such as crop rotation, green manure, compost and biological pest control. Rangeland: vast natural landscapes in the form of grasslands, shrublands, woodlands, wetlands, and deserts. Overgrazing: is herbivory that extracts an unsustainable yield of floral biomass from an ecosystem

Process where arid and semi-arid land’s productivity drops >10%. Human activity is the main cause of it. Moderate = 10-25% Severe = 25-50% drop Growing problem in the world!

Reduce: Overgrazing, Deforestation, and Destructive farming. Plant trees & grass to hold water. Will require $10-22 billion annually for next 20 years. Less than $ 1 bill/year is spent on it right now.