Soil Degradation Overview

Soil Degradation

• Soil degradation is a decline in soil's ability to provide ecosystem goods and services, caused by deterioration of physical, chemical, and biological properties.
• It's a growing global concern affecting productivity and global climate.
• Impacts water and energy balances, and disrupts carbon, nitrogen, sulfur, and other element cycles.

Types of Soil Degradation

Physical Degradation

• Definition: Deterioration of soil's physical properties.
• Compaction: Soil densification reducing pores, increasing runoff and erosion.
• Soil erosion: A three-stage process (detachment, transportation, deposition). Rainfall weakens soil, leading to slope movement when water accumulates. Topsoil loss often exceeds formation rate. Ethiopia faces significant erosion (an estimated 42 tons lost per hectare annually).
• Causes: Rainfall intensity, slope steepness, other climate factors.

Biological Degradation

• Definition: Reduction in soil organic matter, biomass carbon, soil fauna activity and diversity.
• Causes: High soil and air temperatures (especially in the tropics), and excessive or inappropriate chemical use.

Chemical Degradation

• Definition: Decline in soil nutrients, pH, and base saturation.
• Causes: Nutrient depletion, excessive leaching (cation loss in low-activity clay soils), toxic chemical buildup, elemental imbalance.

Causes of Soil Degradation

• Natural causes: Topography and climate (steep slopes, floods, storms, high winds, droughts).
• Human-induced causes: Deforestation, overgrazing, unsustainable agricultural practices (agrochemicals misuse, poor conservation), over-extraction of groundwater.

Soil Erosion Control Measures

• Goal: Reduce erosion to a sustainable level without unacceptable environmental harm.
• Rationale: Erosion is a natural process, but can be mitigated.
• Biological Control Measures: Vegetative strips, plantations, reforestation. Helpful to prevent splash erosion, reduce runoff velocity, increase surface roughness, and improve infiltration.
• Physical Control Measures: Techniques to control water and wind movement over the soil. Examples include terracing, check dams, gabions, contour ploughing, soil bunds (common in Ethiopia).