5.3 - Soil Degradation and Conservation

Processes that take away the soil (erosion)

• occurs when there is no or little vegetation on the soil

• wind and water erosion

processes that make the soil less suitable for use or less fertile

• loss of chemicals/nutrients (leaching)

• addition of chemicals (pollution)

Commercial industrialised food production reduce what?

Soil fertility more than small-scale subsistence farming

Types of soil erosion due to water

• Gullying

Gullying

Channels develop on hillsides following rainfall. Over time they get deeper and deeper

Wind Erosion

Drier soils have the top layers consistently removed

Chemical Degradation Examples

Salinisation

Acidification

Nutrient Depletion

Chemical Pollution

Salinisation

Water evaporates leaving salts behind. Soil becomes saline. Common in areas with high levels of evaporation (arid areas and heavily irrigated areas)

Acidification

Increase in hydrogen ion content in the soil. Lowers soil pH. Caused by acid deposition, use of ammonium fertilisrs, & leaching/removal of nutrients from the soil. Ammonium is converted by bacteria in the soil into nitrates & hydrogen ions

Nutrient Depletion

Due to over exploitation (continual cropping without replacing lost nutrients). Reduces soil fertility

Chemical Pollution

Accumulation of toxic metals. Eutrophication. Use of pesticides or oil spills

Physical Degradation

• Soil compaction from heavy farming machinery & animals

• Air spaces between particles are lost which means soil is more easily waterlogged & roots can’t penetrate

• Makes soil more vulnerable to water & wind erosion

Human activities that lead to soil degradation

• Overgrazing

• Overcropping

• Deforestation

• Unsustainable agriculture

Overgrazing

Too many animals grazing in the same area. Plants can’t recover. Leads to bare patches with no plants. If plants do survive, their roots never develop properly

Overcropping

Depletes soil nutrients. Makes the soil friable (dry and susceptible to wind erosion). Nutrients are not restored. Increased risk of crop failure then wind erosion

Deforestation

Removal of vegetation leads to exposure of soil (rainfall is not intercepted by plants which reduces water infiltration). Tropical rainforests are in areas with very high precipitation. Massive amounts of water erosino. Leaves slow down rain, roots bind the soil.

Unsustainable Agriculture

• total removal of crops (leaves bare soil)

• growing crops in rows with bare soil in between

  • especially bad if rows are in the direction of the slope

• plowing in the direction of the slope. leaves ready-made channels for rainwater to flow down, taking soil with it

• excessive use of pesticides. Makes soil toxic through toxification

• irrigation, when the water evaporates before it reaches the crops as it leads to salinization

• monocultures, the same nutrients are depleted from the soil and the soil loses its fertility

Urbanisation

More people now live in cities than in rural areas. Increased run off may lead to extra erosion down stream. Many major cities expanded from settlements that were based on agriculture, therefore they are expanding into prime agricultural land

Soil Conditioners

Materials that are added to soil to improve plant growth and health.

The type of ______ added depends on the current soil composition, climate and the type of plant. Some soils lack nutrients necessary for proper plant growth and others hold too much water or too little water. It helps correct the soil’s deficiencies

Ex: Lime can be added to soil to make it less acidic or Organic materials (manure) can be added to soil to replace depleted plant nutrients.

Wind Reduction Techniques

Shelter Belt, Wind Breaks

Shelter Belt

Involves planting trees or hedges to act as a wind barrier to a crop or field. They can reduce the wind speed by up to 50% and so reduce soil movement in the protected area

Wind Breaks

Barriers used to reduce and redirect wind. They usually consist of trees and shrubs but can also be crops, grasses, fences or other materials

Cultivation Techniques

Terracing

Terracing

A levelled section os a hilly slope, often such land is formed into multiple terraces giving a stepped appearance.

Useful method of soil conservation as it slows or prevents the rapid surface run off of water that occurs on steep slopes

Contour Farming

Ploughing and cultivating at right angles to the natural slope of the land to create a series of stepped ridges used for planting crops.

Benefits:

• Soil erosion can be reduced by as much as 50%

• Increased soil retention encourages root development, binding the soil and preventing erosion

• Limites the release of nutrients/particulates into nearby river systems of lakes, minimising harmful effects such as eutrophication

• Can disrupt wind currents, therefore reducing wind erosion

Restrictions:

• Stepped topography may hinder modern (mechanised) farming practices

Improved Irrigation Techniques

Carefully planning irrigation systems that can reduce evaporation rates. Salinisation would also be greatly reduced

Drip Irrigation (trickle flow irrigation)

Network of pipes covering a field that let water drip slowly into the soil so that all water is absorbed. Common in desert areas (ex. israel)

Stopping the ploughing of marginal lands

This is land that is poor in quality and will not support much plant life for long. As a result it is then left bare and vulnerable to increased soil erosion

Marginal Lands

Poor-quality land that is likely to yield a poor return.

Crop Rotation

Growing when food is in season

Helps maintain the fertility of the soil

Unsustainable agricultural techniques

techniques that can be applied over a long period of time without a decrease in productivity or increased fertilisers