Land Degradation and Reclamation
By
Dr. Daldoum Mohamed Ahmed
University of Khartoum, Faculty of Forestry,
Postal Code 13314 Shambat, Emails:
[email protected], Sudan
Contents
1/ Definitions of land degradation
2/ Forms of degradations and extends
(i) Wind erosion
(ii) Water erosion
(iii) Human induced land degradation
3/ Social and economical impacts
4/ Reclamation measures
(i) Afforestation/reforestation
(ii) Sustainable land use
(iii) Chemical procedures
(iv) Physical and mechanical procedures
5/ Conclusions
1/ Definitions of land degradation
Land degradation is defined as a process that lowers the current
and/or future capacity of the land to produce goods and
services
In most cases no clear distinction is made between land and soils;
land is often employed as synonymous to soils
Land degradation can either be as a result of natural hazards or due to
unsuitable or inappropriate human practices
Natural hazards:
* Precipitations (rains and snow): particularly heavy
continuous rains and snow in hilly areas.
* Winds of high velocity
* Radiation and temperatures
* Relief: topography and slope
* Fires
Human impacts
2/ Forms of degradations and extends
(i) Wind erosion involves:
* Loss of topsoil (sweeping, dust movement)
* Terrain deformation
* Over-blowing (sand creep, deposition)
(ii) Water erosion involves:
* Loss of topsoil (rills, gullies, sheet)
* Mass movement (land slides in hilly areas, bank destruction
of rivers)
* Terrain deformation
* Reservoir and water channels siltation and sedimentation
* flooding
* Destruction of vegetation cover
Types of Gully erosion
Slides of river banks
Sedimentation of channel beds
Rain drop splashing
Sheet erosion after fire
Sheet erosion on
a bare land
Land slide and road destruction
Erosion induced by mechanical works
Alkali soil. Emery Deep Mine (USA).
The chemical and physical deterioration processes of wind and
water erosions are:
Chemical:
* Loss of nutrients
* Loss of organic matter
* Salination/ alkalization/sodicity
* Acidification
* Pollution/contamination/toxicity
* Eutrophication
Physical:
* Compaction, sealing and crusting
* Soil structure deterioration
* Soil texture misbalancing
* Water-logging
* Lowering of water table
Biological deterioration
(iii) Human induced land degradation
* Agriculture mismanagement (mechanization,
unbalanced use of fertilizers, irrigation)
* Infrastructure and civil engineering work (roads,
dams, bridges)
* Mining and petroleum oil exploitation
* Industrial activities
* House hold and municipal wastes
* Deforestation
* Overgrazing
* Fires
3/ Social and Economic Impacts
Soil fertility (physical and chemical) decline due to degradation is a
major factor in decreasing agricultural productivity and yields.
The consequences are:
* Less food (for both human and animal) and cash income and
hence famines
* Population displacement/migration and fragility to all
circumstances
* Conflicts and war over the meager and shrinking resources.
Land degradation can engender environmental hazards with more
devastating effects (torrents, floods, sedimentation, dust tempests)
on dwellings, installations and infrastructure
Land degradation can engender serious sanitary and health problems
Over all problems of land degradation can overcome the capacities
of local and national authorities to the extent that solicitation of
the international aid is inevitable
4/ Reclamation measures
(i) Afforestation/reforestation:
Forests and trees effects on controlling land and soil degradation are
by far the most efficient:
1/ They can intercept rainfall and then attenuate the splashing impact
of the rain drops on the soil
2/ They can intercept and absorb the incident radiation and shade the
ground and hence reduce direct evaporation
3/ They cover the soil and so can protect it from erosive effect of
strong violent winds
4/ They add considerable amounts of organic matter which when
decomposed can release valuable nutrients
5/ Litter addition to the forest floor and action of roots and fauna can
increase water infiltration rate into the soil
6/ Root reticulum and exudates can bind soil particles together
ameliorating soil structure and hence reduce erosion and
enhance water circulation and retention
7/ they render other services and goods
(ii) Sustainable land use
Irrational agricultural practices are among the most damaging factors
to land and soils
Sustainable use of land for agriculture should seek a balance between:
Land capabilities – Practices –Inputs – Outputs
* Land capabilities are limited in space and time, and even the type
one land (S1) can be depleted or seriously deteriorated if put under
continuous cultivation
* Practices should be carefully planned and implemented: The role
of education, training and adoption of appropriate technologies is
crucial for sustaining the land production potentials. Now, there is
strong tendency to go back to natural production “Organic
Farming” and Agroforestry
* Inputs should be carefully selected and used for the specific land
type and production aims
* Sustainability and targeted Outputs are apparently in conflict,
because greater outputs should be generated to satisfy the needs for
the ever increasing voracious population (consumers)
(iii) Chemical procedures
The important problems and their remediation are:
1/ Soil nutrient depletion, resulting from leaching, excessive usage or
natural deficiency are rectified by adding appropriate chemical
and organic fertilizers
2/ Soil salinity, alkalinity and sodicity are mitigated by adding
gypsum (CaSO4.2H2O) and abundant leaching with water
3/ Soil acidity is treated by liming materials (CaCO3, CaO, CaMg
(CO3)2; Ash, OM; basic cations
4/ Toxic metals and contaminants can be eliminated and neutralized
by a combined procedures using anti-toxicants materials and
leaching; and also by quarantine measures and planting trees
5/ Choice of resistant crops: Most of these problems can be overcome
by using adapted crops particularly to salinity and acidity
(iv) Physical and mechanical procedures
Many methods are used to alleviate physical deterioration
of the soils:
1/ Checking soil movement by erecting mechanical or live
barriers: like earth bunds; rock dams; terracing; mulches
(grass, straw-hay, sawdust); wind breaks and shelterbelts;
or by cultivation choices, like: contour plowing; strip
cropping; cover crops
2/ Promoting water infiltration: most of the above
mentioned methods are used plus procedures to prevent
soil compaction and encrustation by appropriate tillage
methods
3/ preventing water logging, perching and siltation by
adequate drainage methods, both at the surface and
subsurface levels
Fences to treat steep slopes
before planting
Forage trees planted
along the risers
Control of gully erosion by live
breaks
Women working on land
reclamation
Terrace building and cultivation
Stone risers in a valley
Land mulching by biosolids
Land mulching by grass
5/ Conclusions
• Land degradation (change) as a natural process can not
be stopped altogether, and this has to be clear to all,
through education and raising awareness for this fact
• People have to improve their practices in order to
conserve lands and use them in sustainable manners
• Technologies and innovations bring about significant aid
to overcoming land degradation consequences and
boosting the returns from lands
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