Unit VII: Mineral and Soil Resources

Soil: A Renewable Resource

I. Formation of Soil

• Soil is a potentially renewable resource: 200-1000 years to form 1inch topsoil

• Complex mixture of eroded rock, mineral nutrients, decaying organic matter, water, air and living organisms Formed by the physical, chemical and biological breakdown of rock during weathering.

• Main factors in soil formation: climate, biota, topography, parent material, time

• Soil is the basis of terrestrial life.

II. Layers in Mature Soils

• Mature soils are arranged in a series of horizontal layers- soil horizons- each with a distinct texture and composition. A cross sectional view is a soil profile.

O: surface litter layer: Consists of fallen un decomposed or partially decomposed leaves, twigs, crop or animal waste and fungi. Normally brown or black

A: Topsoil: porous mixture of partially decomposed plant and animal bodies-humus-and inorganis clay, silt and sand.

B: Subsoil: inorganic material; partially broken down rockC: Parent Material: un-weathered bedrock

II. Layers in Mature Soils

• Spaces or pores between solid organic and inorganic particles contain water and oxygen (needed for cell respiration in roots)

• Infiltration: downward movement of water through soil

• Leaching: as water seeps down, it dissolves various minerals and organic matter from top layers and transports them to lower layers

• Soil profiles vary by ecosystem D:\Media\LITE_15e\PowerLectures\chapter3\Animations\soil_profiles.html

III. Biology of Soil

• Bacteria, fungi, actinomycetes, protozoa and nematodes

• mostly microscopic decomposers.

IV. Properties of Soil• Physical

Temperature: soil not air temp that is important to seed germination. Certain pests and diseases thrive at different temps

Texture: property used to describe the relative proportion of different grain sizes of mineral particles in a soil: clay, silt, and sand. Soil texture classification is based on the fractions using a soil triangle.

Loam: Soil with roughly equal parts of each.

Structure the arrangement of the solid parts of the soil and of the pore space

located between them.

IV. Properties of Soil-Porosity

• The volume of all the open spaces (pores) between the solid grains of soil. • The smaller the particle size the greater the porosity. Clay has small particles and the largest

water holding capacity. Sand has large particles and a low porosity

IV. Properties of SoilPermeability-allows water and air to flow.

IV. Properties of Soil-Chemical Properties

• pH: Often referred to as soil acidity. Important in determining which plants will grow because it influences nutrient solubility and thus nutrient uptake.

Too acidic: add lime Too alkaline: add sulfur

• Soil Nutrients: Macronutrients(N,P,K,S,Ca,Mg)Micronutrients (Fe,Mn, Zn, Cu, Mo, Co, Cl)Fertilizers contain N,P,K

Role of Soil Nutrients

• N needed for production of amino acids/proteins; important for photosynthesis

• P important component of nucleic acids (transfer of genetic info)

phosphoproteins and phospholipids.• K enzyme activator that allows stomates

to open and close and water vapor and oxygen to move in and out of plant cells

V. Soil Degradation

• Two categories: 1) displacement of soil (erosion) 2) in situ physical and chem deterioration

• Can be a result of 1) natural hazards: climate, steep slopes, frequent flooding2) in-apprpriate use of land-overgrazing, nutrient depletion.

Erosion: The affect of removal of trees or vegetation

• Water Erosion most influential factor on global soil degradation.

• Natural process increased by human land use.

• Many factors: 1) amount of precip

2) soil texture 3) slope 4) ground cover

5) land usehttp://www.hippocampus.org/AP%20Environmental%20Science

Water Erosion in Tennessee

Sheet Erosion: surface water or wind peel off thin layers of soil.

Rill Erosion: fast-flowing little rivulets of surface water make small channels.

Rill Erosion: fast-flowing little rivulets of surface water make small channels.

Wind Erosion

• Like water erosion, wind erosion involves the removal of soil particles by a moving fluid- air. As with water erosion, the finer particles are typically lost first which leads to the loss of the organic matter and nutrients that are generally attached to those particles. The potential final result of continued wind erosion is an area of active barren dunes

• Blowing soil can also reduce seedling survival and growth, depress crop yieldsand increase the susceptibility of plants to certain types of stress, including diseases.

Dust Bowl• http://www.youtube.com/watch?v=x2CiDaUYr90• 1930’s: Poor farming practices and drought.• Farming techniques that worked in the North and East

did not work on central and Southern Plains. • Utilized mechanized farming techniques as a way to

increase profits. Many bought plows and other farming equipment, and between 1925 and 1930 more than 5 million acres of previously unfarmed land was plowed

• The skies could darken for days- homes could have a thick layer of dust on furniture. In some places the dust would drift like snow, covering farmsteads.

• Soil Conservation Service formed as a result of the Dust Bowl-created soil conservation districts

Soil Degradation

• Desertification: Degradation of land in arid and semi-arid regions due drought and overgrazing. Results in loss of biodiversity and loss of productive capacity.

• Salinization: Soil degradation caused by over irrigation: irrigated water contains salts that, when water evaporates are left behind.

• Water logging: Problem associated with excessive irrigation on poorly drained soils where water can't penetrate deeply. When soils are water logged, air spaces in the soil are filled with water, and plant roots essentially suffocate - lack oxygen.

Severe desertification: Sand dunes threaten to take over an oasis in the Sahel

region of West Africa.