دراسة لاستصلاح الاراضى الصحراوية الساحلية(1)

Reclaiming desert land







Repairing damaged land

Land reclamation or Land rehabilitation is also the process of cleaning up a site that has sustained environmental degradation, such as those by natural cause (desertification, ...) and those caused by human activity (strip mining, ...). Land reclamation is often done in these sites to allow for some form of human use (such as a housing development) or to restore that area back to its natural state as a wildlife habitat home.


Reclaiming desert land

Land reclamation in deserts involves

 setting-up reliable water provisioning (eg by digging wells or placing long-distance water pipes)
 stabilizing and fixating the soil
Stabilizing and fixating the soil is usually done in several phases.

The first phase is fixating the soil to such extent that dune movement is ceased. This is done by grasses, and plants providing wind protection such as shelterbelts, windbreaks and woodlots. Shelterbelts are wind protections composed of rows of trees, arranged perpendicular to the prevailing wind, while woodlots are more extensive areas of woodland. [10]

The second phase involves improving/enriching the soil by planting nitrogen-fixating plants and using the soil immediately to grow crops. Nitrogen fixating plants used include clover, yellow mustard, beans, ... and food crops include wheat, barley, beans, peas, sweet potatoes, date,olives, limes, figs, apricot, guave, tomato, certain herbs, ... Regardless of the cover crop used, the crops (not including any trees) are each year harvested and/or plowed into the soil (eg with clover, ...); in addition a each year the plots are used for a another type of crop (known as crop rotation) to prevent depleting the soil on specific trace elements.

A recent development is the Seawater Greenhouse and Seawater Forest. This proposal is to construct these devices on coastal deserts in order to create freshwater and grow food [11]
A similar approach is the Desert Rose concept [12]
These approaches are of widespread applicability, since the relative costs of pumping large quantities of seawater inland are low[13].
Another related concept is ADRECS - a proposed system for rapidly delivering soil stabilisation and re forestation techniques coupled with renewable energy generatio

Land reclamation in deserts involves
 setting-up reliable water provisioning (eg by digging wells or placing long-distance water pipes)
 stabilizing and fixating the soil
Stabilizing and fixating the soil is usually done in several phases.
The first phase is fixating the soil to such extent that dune movement is ceased. This is done by grasses, and plants providing wind protection such as shelterbelts, windbreaks and woodlots. Shelterbelts are wind protections composed of rows of trees, arranged perpendicular to the prevailing wind, while woodlots are more extensive areas of woodland. [10]
The second phase involves improving/enriching the soil by planting nitrogen-fixating plants and using the soil immediately to grow crops.Nitrogen fixating plants used include clover, yellow mustard, beans, ... and food crops include wheat, barley, beans, peas, sweet potatoes,date, olives, limes, figs, apricot, guave, tomato, certain herbs, ... Regardless of the cover crop used, the crops (not including any trees) are each year harvested and/or plowed into the soil (eg with clover, ...); in addition a each year the plots are used for a another type of crop (known as crop rotation) to prevent depleting the soil on specific trace elements.
A recent development is the Seawater Greenhouse and Seawater Forest. This proposal is to construct these devices on coastal deserts in order to create freshwater and grow food [11]
A similar approach is the Desert Rose concept [12]
These approaches are of widespread applicability, since the relative costs of pumping large quantities of seawater inland are low[13].
Another related concept is ADRECS - a proposed system for rapidly delivering soil stabilisation and re forestation techniques coupled with renewable energy generation[14].
Land rehabilitation is the process of returning the land in a given area to some degree of its former state, after some process (industry, natural disasters etc.) has resulted in its damage. Many projects and developments will result in the land becoming degraded, for example mining, farming and forestry.
While it is rarely possible to restore the land to its original condition, the rehabilitation process usually attempts to bring some degree of restoration. Modern methods have in many cases not only restored degraded land but actually improved it, depending on what criteria are used to measure 'improvement'.
Soil salinity control relates to controlling the problem of soil salinity and reclaiming salinized agricultural land.
The aim of soil salinity control is to prevent soil degradation by salinization and reclaimalready salty (saline) soils. Soil reclamation is also called soil improvement, rehabilitation, remediation, recuperation, or amelioration.
The primary man-made cause of salinization is irrigation. River water or groundwater used in irrigation contains salts, which remain behind in the soil after the water has evaporated.
The primary method of controlling soil salinity is to permit 10-20% of the irrigation water toleach the soil, be drained and discharged through an appropriate drainage system. The salt concentration of the drainage water is normally 5 to 10 times higher than that of the irrigation water, thus salt export matches salt import and it will not accumulate.


The soil salinity problem


Irrigated saline land with poor crop stand
Salty (saline) soils are soils that have a high salt content. The predominant salt is normally sodium chloride (NaCl, "table salt"). Saline soils are therefore also sodic soilsbut there may be sodic soils that are not saline, but alkaline.
Salty soils are a common feature in irrigated lands in arid and semi-arid regions as well as areas that have poor or little crop production. [1] The problems are often associated with high water tables, caused by a lack of natural subsurface drainage to the underground. Poor subsurface drainage may be caused by insufficient transport capacity of the aquiferor because water cannot exit the aquifer for instance, if it is situated in a topographicaldepression.
Worldwide, the major factor in the development of saline soils is a lack of precipitation. Most naturally saline soils are found in (semi)arid regions and climates of the globe.
Primary cause
The primary cause of man-made salinization is the salt brought in with irrigation water. All irrigation water derived from rivers or groundwater, however 'sweet', contains salts that remain behind in the soil after the water has evaporated.
For example, assuming irrigation water with a low salt concentration of 0.3 g/l (equal to 0.3 kg/m³ corresponding to an electric conductivityof about 0.5 dS/m) and a modest annual supply of irrigation water of 10,000 m³/ha (almost 3 mm/day) brings 3,000 kg salt/ha each year. In the absence of sufficient natural drainage (as in waterlogged soils) and without a proper leaching and drainage program to remove salts, this would lead to a high soil salinity and reduced crop yields in the long run.
Much of the water used in irrigation has a higher salt content than in this example, which is compounded by that fact that many irrigation projects use a far greater annual supply of water. Sugar cane, for example, needs about 20000 m3/ha of water per year. As a result, irrigated areas often receive more than 3,000 kg/ha of salt per year and some receive as much as 10,000 kg/ha/year.
Secondary cause
The secondary cause of salinization is waterlogging in irrigated land.
Irrigation causes changes to the natural water balance of irrigated lands. Large quantities of water in irrigation projects are not consumed by plants and must go somewhere. In irrigation projects it is impossible to achieve 100% irrigation efficiency where all the irrigation water is consumed by the plants. The maximum attainable irrigation efficiency is about 70% but usually it is less than 60%. This means that minimum 30%, but usually more than 40% of the irrigation water is not evaporated and it must go somewhere.
Most of the water lost this way is stored underground which can change the original hydrology of local aquifers considerably. Many aquifers cannot absorb and transport these quantities of water and, the water table rises leading to water logging.
Water logging causes three problems:
 the shallow water table and lack of oxygenation of the root zone reduces the yield of most crops
 it leads to an accumulation of salts brought in with the irrigation water as their removal through the aquifer is blocked
 with the upward seepage of groundwater more salts are brought into the soil and the salination is aggravated
Salt affected area
Normally, the salinization of agricultural land affects a considerable area of irrigation projects, on the order of 20 to 30%. When the agriculture in such a fraction of the land is abandoned, a new salt and water balance is attained, a new equilibrium is reached, and the situation becomes stable.
In India alone, thousands of square kilometers have been severely salinized. China and Pakistan do not lag much behind (perhaps China has even more salt affected land than India). A regional distribution of the 3,230,000 km² of saline land world wide is shown in the following table derived from the FAO/UNESCO Soil Map of the World [2] .