Chapter 11: Soil - Foundation for Land Ecosystems

Goal 2: End hunger, achieve food security and improved nutrition, promote sustainable agriculture.

Importance of Soil

• Healthy soil is foundational to human civilization, as 95% of all food grown globally relies on soil. A diverse array of organisms resides in soil, contributing to its health and fertility.

• Healthy soil is essential for biodiversity, as it supports various plant and animal life, which in turn supports ecosystem services such as pollination and pest control. Maintaining soil health is critical for sustainable land practices and ecosystem stability.

Soil Composition and Characteristics

• Definitions:

  • Soil: solid material of geological and biological origin that supports plant growth, acting as a medium for plant roots

  • Productive topsoil is formed through complex interactions between organisms, organic waste, and minerals over long periods.

• Most soils develop over hundreds or thousands of years and are categorized by profile, structure, and type, influencing their usability for agriculture. The three primary soil horizons are the topsoil (A horizon), subsoil (B horizon), and parent material (C horizon).

Soil Texture

• Soil Texture: relative proportions of sand, silt, and clay in the soil, significantly affecting its physical properties and behaviors.

  • Clay: particles smaller than 0.004 mm, providing excellent nutrient retention but limiting drainage

  • Silt: particles between 0.004 to 0.06 mm, offering a balance of nutrient retention and drainage

  • Sand: particles between 0.06 to 2.0 mm, promoting excellent drainage but poor nutrient retention

  • Loam: ideal soil for agriculture with a composition of 40% sand, 40% silt, and 20% clay, enhanced with organic matter for optimum water retention and nutrient availability.

Soil Texture Triangle

• A visual representation represents the proportions of clay, silt, and sand, guiding effective soil management practices by determining soil types.

Soil Properties

• The size of soil particles directly influences the soil's physical properties; larger particles result in larger spaces, while smaller particles create more surface area for interactions.

• Soil texture significantly affects:

  • Water infiltration: the speed at which water enters soil

  • Water holding capacity: how much moisture the soil can retain

  • Nutrient retention: the soil's ability to hold essential nutrients

  • Aeration: the exchange of gases in the soil, critical for root respiration.

Soil and Plant Relationships

• A healthy root environment requires a balance of minerals, nutrients, water, oxygen, and an appropriate pH level, which are all influenced by soil properties.

• Soil Fertility Factors:

  • Depth: deeper soils provide more resources for plants

  • Texture: affects root growth and water availability

  • Drainage: essential to prevent root rot and promote healthy growth

  • Nutrient availability: directly impacts crop productivity tied to good soil condition and fertility, emphasizing the importance of soil management to maintain crop yields.

Macronutrients Essential for Plants

• Main macronutrients crucial for plant growth include Carbon (C), Hydrogen (H), Oxygen (O), Phosphorus (P), Potassium (K), Calcium (Ca), Iron (Fe), and Magnesium (Mg).

• Key nutrient deficiencies can lead to stunted growth and poor plant health, showcasing the need for balanced fertilization practices.

Soil Nutrient Dynamics

• Leaching: the process where nutrients are washed from the soil, contributing to reduced fertility and environmental pollution.

• Organic vs. inorganic fertilizers: Organic fertilizers typically maintain better soil health and structure, improving nutrient availability and preventing leaching compared to many inorganic alternatives.

Soil Aeration and Compaction

• The soil must allow for adequate air diffusion essential for root respiration; compacted soils severely restrict air and water pathways, resulting in poor plant growth and lower agricultural yields.

Soil pH and Salinity

• Soil pH affects plant adaptation, as most plants thrive in neutral pH ranges (6-7). Soil acidity or alkalinity can hinder nutrient uptake, influencing crop growth.

• Excessive salinity, often resulting from improper irrigation techniques, can harm root water uptake, negatively impacting plant health, particularly in sensitive crops.

Soil and Carbon

• Soils play a significant role in carbon cycling, storing carbon from organic matter. The rates of decomposition are influenced by environmental factors such as temperature and moisture availability.

• Aerobic versus Anaerobic decomposition:

  • Aerobic decomposition: involves oxygen, producing CO2, and is generally more efficient.

  • Anaerobic decomposition: occurs without oxygen, producing methane (CH4), a potent greenhouse gas, emphasizing the importance of managing soil conditions to mitigate greenhouse gas emissions.

Healthy Soil Community Requirements

• Nutrient-rich and well-structured soil is crucial for supporting both plant life and various microbial communities.

• The presence of organic material is vital for the provision of nutrients, promoting biological activity which aids in soil fertility and structure improvement.

Decomposers and Organic Matter

• Decomposers (bacteria, fungi, earthworms, etc.) break down organic matter, enriching soil and improving its structure and fertility.

• The practice of composting significantly enhances soil organic content, reducing waste and contributing to a sustainable nutrient supply in soils.

Erosion and Its Effects

• Soil erosion leads to the loss of topsoil, which is integral to agricultural productivity and can result in substantial economic losses.

• Prevention methods should include maintaining vegetative cover, applying no-till cropping practices, and utilizing contour farming to reduce erosive forces on soil.

Irrigation Practices

• Types of Irrigation include:

  • Flood: inundates fields but can be inefficient and lead to water loss

  • Spray: utilizes pump systems to disperse water but can be prone to evaporation losses

  • Drip: the most efficient approach, delivering water directly to root zones, minimizing water loss.

• Effective irrigation management is essential to conserve water resources and support sustainable farming practices.

Soil Salinization Risks

• The accumulation of salts disrupts plant growth and is closely linked to poor irrigation practices and the overuse of chemical fertilizers, particularly prevalent in arid regions like the UAE.

Soil Restoration Methods

• Methods for restoring degraded soils include the addition of organic inputs, removal of contaminants, and enhancing the natural soil biota through practices such as cover cropping and reduced tillage.

Desirable Soil Qualities for Agriculture

• Fertile, nutrient-rich, well-structured soils are needed for optimal crop production, as soil health is linked to overall environmental stability and agricultural sustainability, ensuring food security.

Alternatives to Conventional Agriculture

• Sustainable agriculture practices include methods such as aquaponics and hydroponics, which allow for food production with reduced reliance on traditional soil-based cultivation methods.

Summary

• Healthy soils are critical for food production, support ecosystem health, and sustainable land use, ensuring resources for future generations.

• Key challenges encountered include soil erosion, increasing salinity levels, habitat preservation, and effective nutrient management. Addressing these challenges is essential for sustainable agricultural practices and food security.