ALYSIA LECTURE 11 ENVS
Review of Water Resource
Water: A Vital Resource
Unique Properties of Water:
Water molecules are polar due to the presence of hydrogen bonds, which leads to unique physical characteristics like high specific heat and surface tension.
Earth’s Water Supply:
The total water available on Earth, approximately 97% of which is saltwater found in oceans, while only 3% is freshwater.
Freshwater is largely stored in glaciers and ice caps (about 68.7%), with groundwater accounting for about 30.1%.
Hydrologic Cycle:
A continuous cycle involving processes such as evaporation, condensation, and precipitation.
Evaporation: Water transitions from liquid to vapor, increasing kinetic energy.
Condensation: Water vapor cools and transitions back to a liquid state.
Three Potential Destinations of Precipitation:
Surface runoff: Water flows over the land surface into water bodies.
Absorption by Plants: Water uptake by vegetation for sustenance.
Percolation into Groundwater: Movement of water through soil into underground aquifers.
Climate Indicators:
Humidity: The amount of water vapor present in the air.
Relative Humidity: The percentage of moisture in the air compared to the maximum it can hold at that temperature.
Global Precipitation Patterns:
Driven by convection currents like the Hadley cell and influenced by trade winds.
Rain shadows formed on the leeward side of mountains contribute to regional climate differences.
Uses of Fresh Water
Consumptive vs. Non-consumptive Use:
Consumptive Use: Water that is used and cannot be returned to its source (e.g., irrigation).
Non-consumptive Use: Water that can be returned to its source post-use (e.g., hydroelectric power).
Quantitative and Qualitative Concerns:
Management of both the amount and quality of freshwater resources is critical to sustainability.
Human Impacts on the Hydrologic Cycle
Changes to Earth’s Surface: Urbanization and deforestation impact natural water flow patterns.
Climate Change Effects: Alterations in precipitation patterns and increased evaporation rates affecting water availability.
Atmospheric Pollution: Pollutants can alter the properties of precipitation, impacting water quality.
Overdrawing Water Resources: Unsustainable extraction of groundwater leads to depletion of aquifers.
Soil Resource
Importance of Soil Study
Over 90% of food crops are produced via land-based agriculture, making soil protection essential for food production and sustainability.
Historical Context: Civilizations such as the Greek, Roman, and Mayan empires collapsed due to soil degradation.
Soil Erosion Effects: Reduction in agricultural productivity resulting from loss of topsoil.
Environmental Issues: Soil degradation can lead to severe ecological problems, including loss of biodiversity.
The Dust Bowl
Historical Event: The Dust Bowl began in the 1930s due to severe drought starting in 1931.
By 1934, 75% of the U.S. was experiencing drought, affecting 27 states significantly.
Human actions, such as aggressive plowing and deforestation, exacerbated the effects of the drought.
Government Response: The Soil Conservation Act was passed by Congress in 1935 to address soil erosion and degradation caused during this time.
Current Soil Vulnerability
A dust storm in 2014 in Phoenix, Arizona, highlights ongoing soil vulnerability.
Recent Estimates: Up to 35% of the U.S. Corn Belt has experienced loss of carbon-rich topsoil, with mechanical tillage driving erosion, resulting in an approximate 6% decrease in crop yield equating to around $3 billion in losses (Proc. Natl. Acad. Sci. 2021).
Definition of Soil
Soil: “Soil is a mixture of minerals, dead and living organisms (organic materials), air, and water.” – Soil Science Society of America.
Composition: Minerals (45-50%), Pore Space (45-50%), Organic Matter (1-5%).
Soil Formation
Process of Weathering: Soil develops through the weathering of rocks over time.
Involves interactions among parent material (rock), climate, landscape, and organisms.
Dynamic Nature of Soil: Soils evolve with time and age; older soils are generally more weathered.
CLORP Factors: Soil scientists refer to the factors influencing soil formation collectively termed CLORP (Climate, Organisms, Relief, Parent material, Time).
Book Reference: Hans Jenny's work "Factors of Soil Formation" published in 1941 outlines the principles of soil formation.
CLORP: Influencing Factors of Soil Formation
Climate (C): Influences chemical reactions, with temperature and precipitation patterns affecting weathering rates.
Organisms (O): Includes burrowing animals and plant roots that contribute to soil structure and nutrient distribution.
Relief (R): Refers to the topography's effect on sunlight exposure, water runoff, erosion, and organic matter accumulation.
Parent Material (P): The underlying geological material (rocks and sediments) influencing soil mineral content.
Time (T): The age of soil affects its level of weathering, where older soils exhibit greater weathering processes.
Soil Profile
Definition: The soil profile is a description of the different, naturally formed layers within soil, categorized into horizons: O, A, E, B, and C.
O Horizon: Organic layer, rich in decomposed materials.
A Horizon (Topsoil): Rich in organic matter and nutrients, vital for plant growth.
E Horizon: Eluviation zone, where materials are leached.
B Horizon (Subsoil): Accumulates leached materials from above layers.
C Horizon (Parent Material): Contains weathered rock and mineral matter.
Soil Formation and Topsoil Development
Topsoil Formation: Occurs at extremely slow rates, with about one inch taking several hundred years to form.
Interactions: Involves dynamic relationships among organisms, detritus, and mineral particles, leading to nutrient-rich layers essential for agriculture.
Soil Texture
Definition: The relative proportions of sand, silt, and clay in a soil sample.
Sand: Particle size of 2.0 to 0.063 mm.
Silt: Particle size of 0.063 to 0.004 mm.
Clay: Particle size of less than 0.004 mm.
Texture Testing: Conducted using a water and soil mixture in a test tube, allowing particles to settle for classification.
Classification Methodology: Utilizes a soil texture triangle to determine soil type based on particle distribution.
Example: A soil sample with 30% clay, 15% silt, and 55% sand is mapped to its corresponding location on the triangle.
Soil Properties
Influence of Texture on Soil Properties:
Larger particles yield larger pore spaces while smaller particles have greater surface area relative to volume.
Impacts nutrient retention and water holding capacity affecting aeration.
Soil Workability: Affected by texture; clay soils can be difficult to cultivate (too sticky or hard), while sandy soils are easier to work with.
Soil Texture and Properties Summary
Soil Type | Infiltration | Water-Holding Capacity | Aeration |
|---|---|---|---|
Sand | Good | Poor | Good |
Silt | Medium | Medium | Medium |
Clay | Poor | Good | Poor |
Loam | Medium | Medium | Medium |
Loam: Defined as 40% sand, 40% silt, 20% clay, representing optimal soil for agriculture due to balanced properties.
Soil Classification
Soils are categorized by structure and textures, descending from soil order to class levels.
Four Major Soil Orders for Agriculture:
Mollisols: Fertile soils of temperate grasslands, ideal for crops.
Alfisols: Moderately weathered soils of temperate forests, suitable for agriculture with fertilization.
Oxisols: Soils from tropical rainforests; limited agricultural potential due to leaching.
Aridisols: Dryland soils; support industries like livestock but may lead to salinization with irrigation.
Importance of Soil Orders
Mollisols: Known for rich organic material, primarily found in the Midwest U.S., Ukraine, Mongolia, and Argentinian Pampas.
These soils are ideal for growing a variety of crops due to less mineral leaching from rainfall.
Alfisols: Generally suitable for agriculture but require fertilization; found extensively in temperate forest regions.
Oxisols: Characterized by poor agricultural potential; high iron and aluminum content, with weak topsoil.
Aridisols: Characterized by lack of moisture and vegetation, most effective for three intended uses—livestock grazing, seldom crops, mostly non-native vegetation unless irrigated.
Global Soil Distribution Map
A comprehensive map shows the worldwide distribution of the 12 soil orders, vital for understanding agricultural and environmental implications.
Soil and Plant Growth
For optimal plant growth, the soil should provide:
Essential mineral nutrients
Adequate water
Sufficient oxygen levels
Appropriate pH and salinity level
Soil Fertility: Refers to the capacity of soil to support plant growth, often described by the term "tilth" among farmers.
Plant-Soil-Water Interactions
Evaporation and Transpiration: Key processes affecting the soil's water cycle.
Soil water dynamics include factors like infiltration, runoff, and moisture retention.
The Soil Community
A thriving soil community is vital for supporting plant growth, requiring:
Nutrient availability
Adequate nutrient-holding capacity
Proper water holding capacity
Aeration
Near-neutral pH and low salinity
Limiting Factors: The principle of limiting factors explains that the most deficient resource restricts plant growth potential.
Soil texture can be improved through organic matter addition and other ecological interactions.
Soil as a Detritus-Based Ecosystem
Soil supports a myriad of organisms like fungi, insects, and small mammals that consume detritus, promoting layer formation and enriching soil structures.
Nutrient Holding Capacity
Cation Exchange Capacity (CEC): Refers to the soil's ability to hold and exchange cations, including essential elements like Al, Ca, K, Na, Fe.
Higher CEC values correlate to stronger soils due to better nutrient retention capabilities.
Buffering Capability: Influenced by clay types and amounts, CEC helps maintain soil pH stability.
Humus and Soil Structure
Humus: Decomposed organic matter holds water and nutrients; provides a loose structure crucial for supporting growth.
The structural quality differentiates humus-rich soils from loams lacking humus, impacting cultivation practices and ecosystems.
Vitality of Humus in Topsoil
Humus Oxidation vs. Accumulation:
Loss of humus leads to diminished water retention, nutrient capacity, and soil aeration.
Conversely, accumulation enhances these properties, integrating detritus management with retrieval processes.
Soil Degradation
Distinguished by the loss of the soil's ability to sustain plant life and ecosystem functions.
Global Scale: Soil degradation impacts around 200 million hectares, representing approximately 38% of the world's cropland.
Soil Erosion
Defined as the detachment and transportation of soil and humus, primarily by water and wind.
Rates of soil loss on agricultural lands can be 18 to 100 times faster than restoration rates.
Erosion types include splash, sheet, and gully erosion, with vegetative cover acting as a protective measure against loss.
Causes of Erosion
Overcultivation: Exposing soil leads to increased erosion vulnerabilities.
Overgrazing: Results in diminished soil production capacity; Western U.S. rangelands significantly underperform compared to pre-commercial grazing.
Deforestation Effects: Leads to reduced soil stability and erosion due to diminished root systems and less nutrient recycling.
Drylands and Desertification
Cover approximately 41% of the Earth's surface, defined by low precipitation patterns, allowing for specific ecosystems to thrive.
Erosion and excessive agricultural practices risk desertification, characterized by commonly irreversible productivity reductions.
Salinization
Process wherein salt accumulates in soil, primarily due to irrigation practices, rendering millions of acres baren for cultivation.
Soil and Carbon Storage
Soils act as substantial carbon reservoirs, holding three times more carbon than the atmosphere.
Factors driving organic decay rates include temperature, moisture, and microbial community activity, influencing soil carbon storage dynamics amid climate change.
Soil Conservation Practices
Strategies to preserve soil integrity include:
Cover cropping
Minimal or no tillage
Mulching for nutrient retention
Enhancing biomass and biodiversity
Implementation of public policy strategies (e.g., NRCS interventions) to guide sustainable practices.
Agricultural Techniques
No-Till Planting: Reduces soil disturbance while enabling continual cropping; conserves resources and protects soil structure.
Contour Farming and Shelterbelting: Methods to mitigate water flow and wind erosion through strategic land management.
Web Soil Survey
Online database offering comprehensive information on national soil types and maps based on geographic parameters, facilitating land management practices.