Definition and Overview
Soil erosion is the gradual or sometimes rapid removal of the upper layer of soil — the layer richest in organic matter and plant nutrients. This process involves detachment, transport and deposition of soil particles by natural forces such as flowing water, wind, gravity and the mechanical action of falling raindrops. Erosion is most severe in soils with poor aggregation, low humus content, and high proportions of silt or very fine sand. Vegetation strongly reduces erosion by protecting the surface from raindrop impact and slowing surface runoff.
In India, approximately 86.9% of soil erosion is attributed to water and 17.7% to wind. Of the nation’s 173.6 million hectares (Mha) of degraded land, about 144.1 Mha are affected by wind and water erosion (Government of India, 1990). Estimates suggest roughly 5,334 million tonnes (≈ 16.35 tonnes/ha/year) of soil are lost annually, with nearly 29% of that material being carried into the sea and effectively removed from the productive landscape.
Types of Erosion
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Natural (Geological) Erosion
Natural or geological erosion proceeds slowly over long periods and is driven by weathering, water, wind, gravity and glacial movements. The rate of soil loss in undisturbed landscapes is typically balanced by new soil formation through rock and mineral breakdown. This form of erosion is often termed normal erosion because it is part of the long-term landscape evolution process.
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Accelerated Erosion
Accelerated erosion occurs when human activities — such as deforestation, intensive cultivation, overgrazing, mining or construction — disturb the land surface and remove protective vegetation. In such cases, soil is lost much faster than natural regeneration rates, resulting in long-term degradation and loss of productive land.
Causes and Forms of Water Erosion
Water erosion is initiated when raindrops strike exposed soil, breaking aggregates into finer particles that are then transported by surface runoff. The process is exacerbated where vegetation cover is removed by tillage, burning of crop residues, overgrazing, logging, or other land-use changes.
Common Forms of Water Erosion
- Raindrop / Splash Erosion — The direct impact of raindrops dislodges soil particles, compacts the surface, and can form a crust that reduces infiltration and increases runoff.
- Sheet Erosion — The even removal of a thin layer of topsoil over broad areas, especially on gentle slopes. It often goes unnoticed until considerable soil has been lost.
- Rill Erosion — The formation of small, often parallel channels caused by concentrated flow. Rills are small enough to be erased by normal cultivation, but they signify advancing erosion.
- Gully Erosion — When rills deepen and widen to form channels that cannot be removed by regular tillage. Gullies permanently alter the landscape and can isolate sections of land.
- Stream Channel Erosion — Scouring and undercutting of stream banks by flowing water, which changes channel shape and can undermine adjacent land and infrastructure.
Effects and Consequences of Water Erosion
Water erosion produces multiple short- and long-term impacts on the environment, agriculture and infrastructure, including:
- Loss of fertile topsoil: The most immediate effect is the removal of nutrient-rich surface soil and organic matter that supports plant growth.
- Deposition of unproductive materials: Eroded coarse sand and gravels may be deposited on productive land, reducing its value and yield potential.
- Siltation of reservoirs and lakes: Sediment transported from catchments fills storage capacity, reducing water availability for irrigation, drinking and hydropower.
- Clogging of drainage systems: Reduced channel capacity increases flooding risk and damages downstream crops, roads and built infrastructure.
- Lower groundwater recharge: With greater runoff and reduced infiltration, less water percolates to recharge aquifers, diminishing well yields.
- Land fragmentation: Gully formation and channeling divide fields into smaller plots, make mechanized farming difficult, and reduce land value.
Wind Erosion: Process and Impacts
Wind erosion is particularly important in arid and semi-arid regions where rainfall is insufficient and vegetation is sparse. The finer soil particles (silt, clay and organic matter) are the most susceptible to wind transport. Over time, wind erosion shifts the soil texture towards coarser fractions and reduces fertility.
Mechanisms of Wind Erosion
- Saltation: Medium-sized particles (typically 0.05–0.5 mm) move in short hops or bounces close to the ground, driven by wind pressure and impacts from other particles.
- Suspension: Very fine particles become entrained in turbulent airflows and can be carried over long distances, contributing to dust storms and distant deposition.
- Surface Creep: Coarse particles roll or slide along the surface; they are pushed by saltating particles rather than lifted directly by the wind.
Threshold velocity is the minimum wind speed required to initiate movement of soil particles; it depends on particle size, moisture content, surface roughness, and vegetative cover.
Impacts of Erosion on Crop Yield and Farm Management
Erosion affects crop production both directly and indirectly. The principal impacts are:
- Reduced soil moisture retention: Thinner topsoil layers hold less water, increasing drought stress for plants.
- Nutrient loss: Valuable nutrients are removed with eroded soil, often leading to higher fertilizer requirements; nutrients in subsoil are usually lower than in topsoil and cannot fully compensate.
- Soil structural decline: Erosion and surface sealing increase runoff, reduce infiltration, and make seedling emergence more difficult.
- Heterogeneous field conditions: Uneven erosion produces variable soil depths across a field; some patches may retain several inches of topsoil while others are reduced to subsoil, complicating planting schedules, fertilizer application and irrigation management.
Best Management Practices (BMPs) to Control Erosion
Combining multiple BMPs is often the most effective approach to prevent or reduce erosion. The following techniques are commonly used across climates and farm sizes:
Vegetative and Cropping Practices
- Crop rotation: Alternating crop species improves soil structure, reduces pest pressure and supplies different rooting patterns that stabilize soil.
- Cover crops: Planting cover crops in fallow periods protects soil from raindrop impact, reduces runoff and traps nutrients for subsequent cash crops.
- Strip cropping: Alternating strips of erosion-resistant and susceptible crops reduces wind speed at the surface and interrupts runoff paths.
- No-till and reduced tillage systems: Minimize soil disturbance and retain surface residues that shield the soil and enhance infiltration.
Land and Water Engineering Techniques
- Contour cultivation: Tilling, planting and constructing terraces along the natural contours reduces downhill water velocity and encourages infiltration.
- Terracing: Building bench terraces on steep slopes shortens slope length and stores water temporarily to promote sediment deposition and infiltration.
- Grassed waterways: Establishing vegetated channels to convey stormwater safely without causing erosion; they also filter sediment and provide habitat benefits.
- Diversion and drop structures: Engineered channels and small dams redirect or slow runoff to prevent gully formation and control concentrated flows.
- Riparian buffer strips: Vegetation planted along streams and drains traps sediment, reduces nutrient loads and stabilizes banks.
Soil Management and Tillage Options
- Strip rotary tillage: Prepares narrow seedbeds while leaving most of the soil covered by residues, combining benefits of tilled seedbed and residue protection.
- Till planting: Leaves residues in the inter-row area to reduce raindrop impact and minimize soil displacement.
- Annual ridges (ridge tillage): Planting on raised rows formed with minimal spring seedbed preparation; residues between rows help retain moisture and reduce erosion.
- Chiseling: Subsurface loosening that maintains surface residues, improving infiltration without inverting the soil.
- Disking: A shaper to reduce clods and prepare seedbeds; its erosion impact depends on depth and timing because deep disking removes residue cover that protects the soil.
Applied thoughtfully and in combination, these practices substantially reduce the risk of soil loss from both wind and water, help preserve soil fertility, and support the long-term sustainability of agricultural systems.
© Eroded Soils — Prepared for educational and management guidance purposes. Data reference: Government of India (1990) where noted.
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