Welcome to ESS Topic 5: Land – The Earth's Skin
Hey future environmental managers! This chapter, "Land," is incredibly important because soil is literally the foundation of terrestrial life and global food security. If you think of Earth as a living organism, the soil is its vital, life-sustaining skin.
We will be digging into the structure of soil (yes, it's a system!), how we use it to feed billions of people, and the serious environmental challenges that arise when we mismanage this precious resource. Don't worry if this seems tricky at first; we'll break down the layers one by one!
Key Focus: Understanding soil as a system and evaluating the sustainability of different food production methods.
5.1 The Soil System
The Soil Profile and Its Components
Soil is not just dirt! It is a complex, dynamic system that provides ecosystems services like nutrient cycling, water storage, and support for primary producers (plants). It's made up of four major components:
- Mineral Particles: Weathered rock fragments (sand, silt, clay). This is the non-living backbone.
- Organic Material (Humus): Decomposed plants and animals. This makes the soil dark and rich in nutrients.
- Water: Held between the soil particles, crucial for plant uptake and chemical reactions.
- Air: Necessary for aerobic organisms (like bacteria and roots) to respire.
Understanding Soil Horizons
Imagine cutting a slice through the ground—that vertical section is the soil profile, and the horizontal layers are called horizons. Think of this as a multi-story ecosystem!
Memory Aid: "Organic Animals Bury Chunks of Rock"
- O Horizon (Organic): Surface litter, undecomposed or partially decomposed organic matter.
- A Horizon (Topsoil): Dark, rich layer. A mix of mineral matter and humus. This is where most biological activity occurs, and it's essential for farming.
- B Horizon (Subsoil): Lighter color, less organic matter. Accumulation of minerals leached down from the A horizon.
- C Horizon (Parent Material): Partially weathered rock.
- R Horizon (Bedrock): The unweathered solid rock base.
Soil Processes: Transfers and Transformations
Like any system, soil involves inputs, outputs, transfers, and transformations.
Transfers (Movement of material):
- Leaching: Water carries soluble nutrients down the profile (from A to B).
- Erosion: Removal of soil (output) by wind or water.
- Translocation: Movement of material within the soil.
Transformations (Change in material structure):
- Decomposition: Organic matter is broken down into humus and simpler minerals by decomposers.
- Weathering: Bedrock is physically and chemically broken down into mineral particles.
The Importance of Soil Texture
Soil texture is determined by the relative amounts of sand, silt, and clay.
- Sand: Largest particles. Good drainage, poor water retention, poor nutrient holding.
- Clay: Smallest particles (flat plates). Poor drainage (easily waterlogged), high water retention, high nutrient holding.
- Silt: Medium particles.
The ideal soil for agriculture is loam—a balanced mixture of all three. Loam ensures good drainage (from sand) while retaining enough water and nutrients (from silt and clay).
Quick Review: Soil is a vital system with identifiable layers (horizons) and processes (leaching, decomposition) driven by its physical components (sand, silt, clay).
5.2 Terrestrial Food Production Systems
How do we use the land system to feed 8 billion people? The answer lies in diverse food production systems, each with different inputs, outputs, and impacts.
Classifying Farming Systems
We classify farming systems based on scale, labor, and technology:
1. Scale and Resources:
- Subsistence Farming: Food grown only to feed the family or local community. Inputs (labor, fertilizer) are low. Common in LEDCs. Example: A family growing corn and vegetables for themselves.
- Commercial Farming: Food grown specifically to sell for profit in national or international markets. Inputs and outputs are typically very high. Common in MEDCs. Example: Massive fields of soy or wheat harvested by machines.
2. Intensity:
- Extensive Farming: Low inputs of capital, labor, and materials per unit of land area. Requires lots of land. Example: Sheep ranching in dry grassland.
- Intensive Farming: High inputs of capital, labor, and materials per unit of land area. Often involves mechanization and heavy use of fertilizer/pesticides. Achieves high yields. Example: Factory farming or high-tech market gardens.
Common Mistake to Avoid: Intensive farming does *not* always mean commercial. A very small, highly managed organic farm (low area, high input per area) is intensive but might still be subsistence or small-scale commercial.
Inputs, Outputs, and Sustainability
All agricultural systems require inputs (labor, seeds, water, fertilizer, fuel, pesticides) and produce outputs (food product, waste, pollution).
Evaluating Efficiency (Food Per Input)
We often measure the efficiency of food production systems. Systems that produce large amounts of food with minimal energy or land input are considered highly efficient.
Energy Efficiency: The ratio of food energy output to energy input (e.g., fuel used for tractors and fertilizer production).
\[ \text{Efficiency} = \frac{\text{Energy Output (Food)}}{\text{Energy Input (Fuel, Fertilizer, Labor)}} \]
Did you know? Most commercial meat production (especially beef and pork) has very low energy efficiency because energy is lost at each trophic level (the 10% rule). Growing crops directly (e.g., rice or potatoes) is far more efficient.
Socio-Economic and Environmental Impact Comparison
| Feature | Commercial, Intensive (e.g., Industrial Monoculture) | Subsistence, Low-Tech (e.g., Traditional Farming) |
|---|---|---|
| Inputs | High fossil fuel, synthetic fertilizer, pesticides, water, capital. | High human labor, low capital, natural/organic fertilizers. |
| Biodiversity | Very low (monoculture farming kills diversity). | Relatively high (polyculture, mixed crops). |
| Soil Health | Tillage leads to erosion; chemical use degrades soil structure. | Often highly sustainable; utilizes crop rotation and composting. |
| Output | High yield per unit area; focus on cash crops. | Lower yield; focus on diversified staple crops. |
Environmental Impact: Intensive, commercial systems are heavily reliant on fossil fuels and artificial inputs, leading to greenhouse gas emissions, water pollution (eutrophication from fertilizer runoff), and reduced biodiversity. While they feed many people, they often sacrifice environmental health.
Key Takeaway: While high-intensity commercial farming maximizes food output, it often maximizes environmental strain, challenging long-term sustainability. Subsistence systems are often more sustainable but cannot meet global demand.
5.3 Land Degradation and Management
When land is mismanaged, it leads to degradation. Land degradation refers to the reduction in the capacity of land to provide ecosystem goods and services and assure its functions over a period of time.
Major Forms of Land Degradation
The three most important forms of land degradation linked to agriculture are soil erosion, salinization, and desertification.
1. Soil Erosion
Soil erosion is the physical removal of soil material by wind or water, greatly reducing the fertility of the land, as the vital A Horizon (topsoil) is lost first.
Causes related to human activity:
- Overgrazing: Too many animals remove vegetation cover, leaving soil exposed.
- Deforestation: Removing trees destabilizes the soil structure.
- Monoculture: Planting a single crop, often leaving the soil bare for long periods.
- Tillage: Ploughing can expose soil directly to wind and rain.
2. Salinization
Salinization is the build-up of salts in the surface layers of soil. This makes the soil toxic to most crops.
The Process (often linked to irrigation in dry areas):
- Farmers use large amounts of irrigation water to grow crops in arid (dry) areas.
- The water evaporates quickly in the high heat.
- As the water evaporates, any dissolved salts it contained are left behind on the surface.
- Over time, the concentration of salt becomes too high, killing the plants.
3. Desertification
Desertification is the process by which fertile land becomes desert, typically as a result of drought, deforestation, or inappropriate agriculture.
It is a serious problem, especially along the edges of existing deserts (e.g., the Sahel region of Africa). It is caused by a combination of climate change (drought) and unsustainable human practices (overgrazing and overcultivation).
Strategies for Sustainable Land Management
Sustainability requires soil conservation—strategies designed to maintain or improve soil quality and reduce degradation.
These strategies fall into two categories: reducing physical loss (erosion control) and improving soil structure/fertility.
Reducing Erosion and Runoff:
- Terracing: Creating level platforms on slopes to reduce water runoff and soil speed (common in rice farming).
- Contour Plowing: Plowing parallel to the curves of the land, creating small ridges that catch water instead of letting it rush straight down.
- Windbreaks/Shelterbelts: Planting rows of trees or hedges to reduce wind speed and prevent wind erosion.
- Cover Crops: Planting non-cash crops (e.g., clover) during the off-season to protect the soil from rain and bind it together.
Improving Soil Structure and Fertility:
- Crop Rotation: Changing the crop grown in a field each season. This prevents the depletion of specific nutrients and can interrupt pest cycles.
- Use of Organic Fertilizers: Manure or compost improves soil structure (water holding capacity) and adds nutrients slowly and naturally.
- No-Till Farming: Planting seeds directly into the residue of the previous crop without plowing. This dramatically reduces erosion and maintains soil moisture.
Encouraging Thought: Every time you see a farm using contour plowing, you are seeing a positive feedback loop being broken—the farm is preventing the loss of the soil that allows it to grow food!
Key Takeaway: Land degradation is primarily caused by human mismanagement (overgrazing, deforestation, excessive irrigation). Sustainable strategies, like terracing and crop rotation, mimic natural processes to protect the soil system.
Final Review: Land and Systems Thinking
As ESS students, remember to view "Land" as a fully functioning system:
Inputs: Solar energy, rainfall, parent material, human inputs (fertilizer, labor).
Outputs: Crop yield, evaporated water, eroded soil, nutrient runoff.
Processes: Weathering, decomposition, leaching, root growth.
The sustainability of food production depends on maintaining the balance of these processes. If inputs (like irrigation) or outputs (like erosion) exceed the system's capacity, the land will degrade.