1. Formation and Characteristics of Hawaii’s Soils

2. 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.
Soil is one of the environment’s most important resources. Soil, along with sunlight and water, feeds plants, houses organisms responsible for nutrient cycling, affects primary productivity, and influences plant community diversity. Although it is not an easy medium to study, it is worthwhile to delve belowground because soil is a key component to research involving plant and soil community responses to climate change, invasive weed encroachment, and plant community composition and productivity. Consequently, soil is a resource that must be conserved. In order to be conserved it must be adequately studied and understood.

3. The 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

4. Soil 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.

5. Soil Forming Factors
Parental Material: The primary material from which the soil is formed.
Climate: weathering forces break down parent material.
Organisms: All plants and animals living in or on the soil.
Topography: The location of a soil on a landscape can affect how the climatic processes impact it.
Time: All of the above factors assert themselves over time

6. Weathering
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.
Water and CO2 can lead to the acidification of soil in the formation of carbonic acid
Oxidation reactions with iron give soil its characteristic red color
Thermal expansion, frost shattering
physical weathering is the disintegration of rock and soil aggregates, by physical (mechanical) processes acting primarily on pre-existing fractures (e.g. joints, cracks between mineral grains);
Climate and weathering
weathering is an exogenic geomorphic process, i.e. climatically-controlled
it is controlled by moisture, temperature and seasonality, the same parameters that define regional climates
in tropical climates, high temperatures, large annual rainfall and continuous biological activity maintain high rates of chemical weathering
water is the agent of all weatering, except stress release (although water erosion is a mechanism of unloading of rock)
all chemical weathering occurs in soluti

7. Describing 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: to 0.05 mm
Sand: up to 2.0 mm
Soil permeability: how fast water can move downward in a particular soil

8. Sand, 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 structure and texture: texture describes the relative percentages of primary soil particles (sand, silt, and clay); sand, silt, and clay are mineral particles defined by diameter. Soil structure describes how the primary particles are arranged into aggregates or peds. Thus, a soil aggregate comprises many primary particles. Sandy soils often have poor structure; the course texture causes good drainage/poor retention of water. Clay soils with poor structure will have many small pores but few large ones and will thus drain poorly. Clay soils with good structure may have a balance of fine and large pores and thus provide the moderate drainage/ retention required by many crops.

9. Soil 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)

10. Movement 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.

11. Leaching 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.

12. 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.
(NOTE: Alkaline and basic are not interchangeable. However, aside from uncommon examples such as Ammonias, testing Alkaline and testing pH bring about similar results. The higher the Alkalinity, the greater the tendency towards a base.)
Soil pH is an important consideration for farmers and gardeners for several reasons, including the fact that many plants and soil life forms prefer either alkaline or acidic conditions, that some diseases tend to thrive when the soil is alkaline or acidic, and that the pH can affect the availability of nutrients in the soil.
Alkalinity is measured in mg/l as calcium carbonate (CaCO3). It represents a measure of a solution's ability to buffer or neutralize acids. Lakes located in areas of calcareous glacial till (common throughout central and southern Minnesota) will have higher alkalinity than lakes formed on non-calcareous bedrock (common in northeastern Minnesota). Water with alkalinity less than about 75 mg/L could be considered soft, moderately hard, hard, and greater than 300 very hard. ...

13. 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.

14. Soil 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

15. Crop 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.

16. Fertilizers
Fertilizers contain nutrients that improve the quality and quantity of plant growth.
Excessive use of fertilizers can lead to nutrient pollution.

17. 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

18. Aquifers
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.

19. End