Posts Tagged ‘water-holding’

  • Outline how soil systems integrate aspects of living systems.

Soil forms the Earth’s atmosphere, lithosphere (rocks), biosphere (living matter) and hydrosphere (water). Soil is what forms the outermost layer of the Earth’s surface.

Soils are important to humans in many ways:

  • soil is the medium for plant growth, which most of foods for humans are grown in
  • soil stores freshwater, 0.005% of world’s freshwater
  • soil filters materials added to the soil, keeping quality water
  • recycling of nutrients takes place in the soil when dead organic matter is broken down
  • soil is the habitat for billions of micro-organisms, as well as other larger animals
  • soil provides raw material in the forms of peat, clay, sands, gravel and minerals

Soil has matter in all three states:

  • organic and inorganic matter form the solid state
  • soil water form the liquid state
  • soil atmosphere forms the gaseous state

* Soils are an important source for humans and take time to develop and therefore be counted as a non-renewable resource.

The Soil System

O – Organic Horizon:

  • l – undecomposed litter
  • f – party decomposed litter
  • h – well decomposed humus

A – Mixed mineral-organic Horizon:

  • h – humus
  • p – ploughed in field or garden
  • g – gleyed or waterlogged

E – Eluvial or leached Horizon:

  • a – strongly leached, and ash coloured
  • b – weakly bleached, light brown

B – Illuvial or deposited

  • Fe – iron deposited
  • t – clay deposited
  • h – humus deposited

C – Bedrock or parent material

  • r – rock
  • u – unconsolidated loose deposits

Transfers of materials (including deposition) results in reorganization of the soil. There are inputs of organic and parent material precipitation, infiltration and energy-outputs include leaching, uptake by plants and mass movement. Transformations include decomposition, weathering and nutrient cycling.

  • Compare and contrast the structure and properties of sand, clay and loam soils, including their effect on primary productivity.

Soil structure depends on:

  • Soil texture ( the amount of sand and clay )
  • dead organic matter
  • earthworm activity

For optimum struction, variety of pure sizes are required to allow root prevention, free drainage and water storage. Pore spaces over 0.1 mm allow roots growth, oxygen diffusion and water movement where as pore spaces below 0.5 mm help store water.


  • fertile in temperate locations
  • in tropical areas clay is permeable and easily penetrated by roots
  • nutrient deficient / easily  leached in tropics

The more clay present in soil the higher the force needed to pull a plough.

Different soil types have different levels of primary productivity:

  • sandy soil – low
  • clay soil – quite low
  • loam soil – high

Primary productivity of soil depends on:

  • mineral content
  • drainage
  • water-holding capacity
  • airspaces
  • biota
  • potential to hold organic materials

*Shrinking limit: state which the soil passes from having a moist to a dry appearance.

*Plastic limit: occurs when each ped is surrounded by a film of water sufficient to act as a lunricant.

*Liquid limit: occurs when there is sufficient water to reduce cohesion between the peds.

*Field capacity: maximum amount of water  that a particular soil can hold.

  • Outline the processes and consequences of soil degradation.

*Soil degradation: the decline in quantity and quality of soil. It is also erosion by wind and water, biological degradation (loss of humus and plant or animal life), physical degradation (loss of structure, changes in permeability), chemical degradation (acidification, declining fertility, changes in pH, salinity).

Causes of degradation:

  • Overgrazing: reduces the vegetation cover and allows the surface to be vulnerable to erosion. Dry regions are vulnerable to wind erosion.
  • Deforestation: removed of woodland cause roots in the soil to die and exposure to erosion if on slopes.
  • Cultivation: exposure of the bare soil before/after planting can cause large amounts of run-offs and create rills and gullies. Irrigation in hot areas can cause salinization.
  • Climate change: the higher the  temperature and changing precipitation patterns can lead to direct impacts on soil. Higher temperatures cause higher decomposition of organic matter. More precipitation and flooding cause more water erosion and droughts cause more wind erosion.

Many forms and causes of degradations:

  • Water erosion ( 60% of soil degradation)
  • Wind erosion
  • Acidification (toxification), when the chemical composition of the soil is changed.
  • Eutrophication (nutrient enrichment).
  • Desertification can be caused in extreme cases.
  • Climate can intensify the problem and effect of hydrology.

This shows that the soil degradation’s damage is world spread and has occurred on 15% of the world’s total area.

  • Outline soil conservation measures.

Strategies for combating soil degradation is not so common or widespread and to reduce this risk farmers are encouraged and informed about the processes and conservation methods. Farmers are in the need of beginning with extensive management practices like organic farming, afforestation, pasture extension, and benign (gracious) crop production. However to make this work there is a need of policies.

There are a few methods to reduce or prevent erosion, which can be mechanical or vegetation cover and soil husbandry.

Mechanical methods: are used to reduce water flow including bunding, terracing, and contour ploughing. The goal is to prevent and slow down the movement of rain water down the slopes.

Cropping and husbandry methods:

This method is used against water and wind damage.

It focuses on:

  • keeping the crops safe as long as possible
  • keeping the ground and place of the crop stable after harvesting
  • planting a grass crop

Grass crop keeps the action of the roots in binding the soil and also it decreases the action of wind and rain on the soil surface. with increased organic content it allows the soil to hold more water and reduce the mass, movement and erosion and stabilizing the soil structure.

To prevent damage to the soil structure, care should be taken to reduce the use of heavy machinery is necessary especially on wet soils and ploughing on soils that are sensitive to erosion.

Management of salt-affected soils:

The three main ways of managing salt-affected soils is by:

  • flushing the soil with water and leaching the salt away
  • putting chemicals to replace sodium ions on the clay and colloids with calcium ions for example by using gypsum a calcium sulphate
  • reduction in evaporation losses to reduce the upward movement of water in the soil

Summary of the conservations methods:

Both socio-economic and ecological factors have been ignored and integrated approach to soil conservation is needed, non-technological factors like population pressure, social structures, economy and ecological factors can determine the appropriate technical solutions. There are a variety of methods to use like  strip and ally cropping, rotation farming, contour planing, agroforestry, adjusted stocking levels mulching, use of cover crops, construction of mechanical barriers such as terraces, banks and ditches.