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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