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Formation and Formation and Characteristics Characteristics
ofofHawaii’s SoilsHawaii’s Soils
What is Soil?What is Soil?
• Soil is formed from the weathering of rocks and minerals (pedogenesis).
• Serves as a natural medium for the growth of land plants.
• Decaying matter from plant and animals makes the soil thick and rich.
• Shows effects of living and environmental factors.
The Importance of SoilThe Importance of Soil
• Sustain plant and animal life both above and below the surface
• Regulate water and solute flow.
• Store and cycle nutrients.
• Provide support for buildings and structures
Soil CompositionSoil Composition
• Soil generally consists of organic and inorganic materials, water and air.
• The inorganic materials are the rocks that have been broken down into smaller pieces.
• The organic material is decaying living matter (plants or animals).
• The amount of water and air in the soil is closely linked with the climate and other characteristics of the region.
Soil Forming FactorsSoil Forming Factors
1. Parental Material: The primary material from which the soil is formed.
2. Climate: weathering forces break down parent material.
3. Organisms: All plants and animals living in or on the soil.
4. Topography: The location of a soil on a landscape can affect how the climatic processes impact it.
5. Time: All of the above factors assert themselves over time
WeatheringWeathering
• Weathering is the physical breaking-down and chemical alteration of the soil.
• Physical weathering is the disintegration of rock without changing its chemical composition.
• Chemical weathering is the decomposition of soil particles by chemical alteration.
Describing SoilDescribing Soil
• Particle size– Small particles have increased surface area such as clays
retain water.– Large particles provide better drainage, retain very few
nutrients.• Soil texture: is the relative proportion of silt, clay,
and sand in the soil.– Clay: smaller than .002 mm– Silt: 0.002 to 0.05 mm– Sand: up to 2.0 mm
• Soil permeability: how fast water can move downward in a particular soil
Sand, Silt and ClaySand, Silt and Clay
• Sand and silt are the product of physical weathering
• Clay is the product of chemical weathering.
• Clay content has a higher retention of nutrients and water.
• Clay soils resist wind and water erosion better than silty and sandy soils
Soil ProfileSoil Profile
• Soil Horizons: the various layers in the soil.
• Soil Profile: The arrangement of these horizons
• Soil horizons differ in a soil properties such as color, texture, structure, and thickness
• Soil horizons also differ in their chemical and mineral content • the surface horizon (A), the subsoil (B), and
the substratum (C). Some soils have an organic horizon (O)
Movement of Materials in SoilMovement of Materials in Soil
• Eluviation: the movement of material from one place to another within the soil.
• Illuviation: the collection of material that has been eluviated.
Leaching and PesticidesLeaching and Pesticides
• Leaching: the movement of a chemical (natural or synthetic) with water moving downward through soil or rock.
• Pesticides and other contaminants can leach into groundwater. • Pesticide Factors
– Solubility: some pesticides dissolve easily in water and are more likely to move into water systems.
– Adsorbtion: some pesticides become tightly attached (strongly adsorbed) to all soil particles and are not likely to move out of the soil and into water systems.
– Persistence: some pesticides evaporate or break down slowly and remain in the environment for a long time.
Soil Chemistry (pH)Soil Chemistry (pH)
• Soil pH is a measure of the acidity or alkalinity in the soil.
• Soil pH influences the solubility of nutrients.
• Soil pH affects the activity of micro-organisms.
• Most plants enjoy a slightly acidic (pH 6-7) environment.
Soil Chemistry (Organic Material)Soil Chemistry (Organic Material)
• Organic matter… • Enhances water and nutrient holding capacity • Improves soil structure• Enhance productivity and environmental quality• Reduce atmospheric CO2 levels that contribute to climate
change.
Soil ErosionSoil Erosion
• Erosion is the displacement of soil and rock by ocean currents, wind, water, or ice.
• A certain amount of erosion is natural and, in fact, healthy for the ecosystem.
• Erosion Factors
– Precipitation
– Soil composition
– Slope Gradient
– Vegetation
– Land use
Crop RotationCrop Rotation
• Crop rotation is the practice of growing of different types of crops in the same space in sequential seasons
• It avoids the buildup of pathogens and pests
• It seeks to balance the fertility demands of various crops to avoid excessive depletion of soil nutrients.
FertilizersFertilizers
• Fertilizers contain nutrients that improve the quality and quantity of plant growth.
• Excessive use of fertilizers can lead to nutrient pollution.
Hawaiian Soil Profile (Ultisol) Hawaiian Soil Profile (Ultisol)
• Consists of very deep, moderately well drained soils.
• Formed in many layers of volcanic ash, igneous rock with lesser amounts of dust from the deserts of central Asia.
• Slight acidic top layer and strongly acidic sub layer
• Some areas very strongly acidic
AquifersAquifers
• Aquifer: a geologic body which is porous and permeable enough to become saturated with water and yields water when wells are drilled into it.
• Recharge: is water that soaks into the ground and adds to aquifers.
• Rainwater is the main source of recharge in Hawaii.
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