Introduction to Environmental Science. Soil Characteristics. Chapter 11 Soil

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1 Chapter 11 Soil Soil Characteristics It s more than dirt Most soils are 100s of years old Weathering breaks down parent rock Soil Separates (particle types) Sand (largest) Silt Clay (smallest) Plants contribute organic material (humus) Soil development involves complex interaction of plants, decomposers, and minerals.

2 Chapter 11 Soil Soil Texture Texture is the percentage of each type of particle found in the soil. Loam soil (commonly found in nature) is approximately: 40% sand 40% silt 20% clay

3 Chapter 11 Soil Soil Texture Characteristics Larger particles have larger spaces Smaller particles have more surface area per same volume of larger particles Nutrient ions and water molecules cling to surfaces Soil Properties Infiltration Nutrient content Water-holding capacity Aeration (air in the soil) Workability (ease in which soil can be cultivated)

4 Chapter 11 Soil Soil Profile - Horizons Processes of soil formation create a vertical gradient of often distinct layers = horizons Soil profile = slice through the soil horizons Soil profiles differ greatly in content and thickness of layers

5 Chapter 11 Soil Soil Profile - Horizons O humus zone A topsoil zone E zone of leaching Humus = partly decomposed organic matter --> high capacity for holding water and nutrients! Loss of topsoil can result in an 85-90% decline in productivity B subsoil (leached minerals) C Weathered parent material

6 Chapter 11 Soil Soil Classes Examples: Mollisols: fertile grassland soils, rich in humus and minerals, best for farming Oxisols: Soils of the tropical and sub-tropical forest, limited minerals (nutrient poor!) Alfisols: Partially weathered forest soils, shallow, farmed with amendments Aridsols: Desert soils, thin & light colored, susceptible to salination The soil s ability to support plant growth with necessary nutrients is an indication of its soil fertility The loss of nutrients as water passed through soil is leaching.

7 Chapter 11 Soil Fertilizer and Soil Conditions Agriculture often removes nutrients from the soil Fertilizer replenishes soil nutrients Organic fertilizer Plant (compost) or animal (manure) Fallow crops (legumes: clover, lentils, peas) that fix atm N 2 Inorganic fertilizer (chemically derived) more prone to leaching Most plants do best when the ph is near 7 (neutral), but some have adapted to different conditions. Such as saline soils Fungi and Bacteria aid soil fertility by: Transfer nutrients to plant Fix Nitrogen Control nematodes (small worms)

8 Chapter 11 Soil Role of Existing Green Plants Provide organic material which becomes Humus Protects soil from erosion Reduces evaporative water loss

9 Chapter 11 Soil Degradation Erosion Most wide spread and damaging to topsoil Has the most negative impact when the soil is exposed Grass is good at erosion control as it can lay down to let excess water flow (rather than being ripped out) Splash erosion causes small particles to fill pore space in soils which decreases infiltration and aeration As sheet erosion gives way to gully erosion, more land can be denuded (vegetation removed) which leads to wider gullies In arid areas (little vegetation), wind can remove light particles and cause larger stones to compact as Desert Pavement

10 Chapter 11 Soil Degradation Erosion As clay and humus are removed, much of the soils nutrient- and water-holding capacity is lost As drylands experience increased degradation of soil and vegetative cover, they experience desertification Desertification can be a result of climate change and/or poor human land use patterns

11 Chapter 11 Soil Degradation Agricultural Practices Leading to Erosion Overcultivation Over-plowing Not rotating crops Overgrazing Tragedy of the commons All users trying to maximize individual return, but degrading resource. Deforestation Increases leaching of minerals in soil Increases runoff Sedimentation of waterways (world river pollution issue)

12 Global Outlook: Soil Erosion Soil is eroding faster than it is forming on more than one-third of the world s cropland.

13 Chapter 11 Soil Degradation Salinization A process of distilling out dissolved salts in irrigated water and leaving it on the land A form of desertification since land is rendered useless Worldwide an estimated 3.7 million acres of agricultural land are lost annually to salinization and waterlogging

14 Chapter 11 Soil Conservation Alternative Farming Practices No-till planting Contour farming Field Border Wind breaks (Shelter belts) Dry land farming minimize irrigation

15 Chapter 11 Soil Conservation Farm subsidies and the soil Encourage excessive use of pesticides and fertilizer Reduce crop rotation as farmers are locked into one crop by the subsidies Promote continued drawdown of aquifers

16 Chapter 11 Soil Conservation Sustainable agriculture Maintain productive topsoil Keep food safe & wholesome Reduce the use of chemical fertilizers & pesticides Keep farms economically viable MIMIC PRACTICES OF THE PAST!!! Contouring, crop rotation, terracing, little or no chemicals, etc