Extreme environments are the areas where it is difficult to survive and where it is difficult to obtain essential food. Many documents about this topic are based on conventions or workshops realised by the UN in previous years which have been declared: 2005 the Year of food and 2004 Year of rice. The year 2003 has been celebrated as the UN Year of Water, one of the most important resources for life whose reserves are at stake. In fact, the loss of productivity can derive from an unsustainable use of principal resources such as fresh water and lands. The depletion of water resources is, among others, at the origin of the increasing process of desertification.
A decreasing availability of fresh water, or limited access to water, is a major constraint to increasing crop production.
In this respect, a solution could be to preserve water resources and to exploit drought resistance of crop plants, through dry farming, including cultivars with minimum water requirements, or to improve water management practices; we refer for example to a number of solutions invented for water saving, such as dry farming, techniques, irrigation management strategies and irrigation system control, flood irrigation, spray, drip irrigation These methods are very simple and they don't require expensive experiments or materials, but they are based on instinctive solutions.
For example the process of desertification requires:
• Increasing the variety of species;
• Making plant species more tolerant to sand and salt water.
Nevertheless, salt-tolerant species require special approaches that involve breeding and selection of crops.
In saline agriculture, an alternative is to allow the environment to select the crops, to match salttolerant plants with desirable characteristics to the available saline resources.
Another major constraint is the reduced amount of arable land, set aside for other functions: lands suffer the concurrence of industrial, residential, tourist, and infra-structural requirements. This progressive loss of farmable land is on a collision course with the expanding global population, which over the next 30 years is expected to require an increase in food production of 20% in developed countries and 60% in developing nations. The result is that the progressively growing number of inhabitants have to face declining resources.
Desertification is generated by land degradation: the loss of the land's biological productivity is caused by human-induced factors or disasters.
''Disasters will continue to occur, and their social, economic, environmental impact will continue to increase'' (Pearce 2005, p. 436).
Desertification affects one third of the earth's surface and over a billion people. Moreover, it has potentially devastating consequences in terms of social and economic costs (UN, YDD).
''Desertification and drought cause an estimated loss of $42 billion a year from agricultural production, contribute to food insecurity, famine and poverty and can give rise to social, economic, and political tensions that can cause conflicts, further impoverishment and land degradation, according to the Convention's Secretariat.
It is widely recognised that environmental degradation has a role to play in considerations of national security, as well as international stability. Therefore, desertification has been seen as a threat to human security'' (UNCCD Executive Secretary Hama Arba Diallo, IYDD Program, 2006).
Throughout the developing world, there are extensive coastal deserts where only seawater or almost brackish water and sand are available.
The disadvantages of sand and saline water for conventional crops become advantages when and where salt-tolerant plants are used: in fact among the 13 mineral nutrients needed by plants, 11 are present in seawater in adequate concentrations for growing crops. The high aeration quality of sand is also valuable. In addition, the infiltration of water through sand reduces salt build up in the root zone when seawater is used for irrigation.
These lands are often located in areas of high nutritional and economic needs as well, so adaptation requires a vulnerability assessment of the population affected and a resilience assessment of the society involved.
Increased research on the development of salttolerant cultivars of crop species could, with appropriate management, result in the broader use of saline soils. Conventional food crops can be bred or selected to tolerate mildly saline water.
Although careful application is necessary, the combination of sand, seawater, sun and salt-tolerant plants presents a valuable opportunity for many developing countries.
Anything we can do to help crop plants to cope with environmental stresses will also raise the quality and quantity of food for those who need it most. They will also serve to enlarge the variety of food.
The direct use of seawater for agriculture is probably the most challenging potential application. This would be based on genetic experiments, it may be the only viable solution for nutrition needs worldwide.
Since environmental stress due to salinity is one of the most serious factors limiting the productivity of crops, the innovation of the salt-tolerance gene introduced by Eduardo Blumwald, who led the research team at the University of Toronto, will have significant implications for agriculture worldwide. The gene that controls increased production of the transport protein was taken from Arabidopsis, a relative of the cabbage that is commonly used in plant research.
In addition to the desertification advance there is the increasing process of salinisation of soil and water, induced by human activity, most of all by irrigation itself and the large use of fertilisers; or induced by natural phenomena i.e. salt water ingress caused by inundation, erosion, sea-level rise, subsidence, or derived from extreme events of tectonic origin, such as tsunamis, or from climate change, such as typhoons and hurricanes.
Worldwide, an estimated 24.7 million acres (10 million hectares), of once agriculturally productive land, are being lost annually because of irrigation-induced salinity, according to the US Department of Agriculture. Crop production is limited by salinity on 40% of the world's irrigated land and on 25% of irrigated land in the United States. Crop irrigation is an age-old practice that allows farmers to be less dependent on seasonal rainfall and the uncertainties of the weather. However, irrigation also increases the salinity of soils and water by depositing in the fields soluble salts such as sodium, calcium, magnesium, potassium, sulfate and chloride that the water has picked up from the soils and rocks it has passed through. Eventually, these salts accumulate in the irrigated soils at levels which decrease the vigour and productivity of the crops grown there.
Salty irrigation water wreaks havoc on most plants by upsetting their ability to take in water through their root cells. In fact, if salt concentrations in the soil are very high, the flow of water into the plant is actually reversed and the plant dehydrates, and dies as water is drawn out of its cells.
Salinity stress is one of the most serious factors limiting the productivity of agricultural crops, but previous studies have shown that exogenous fatty acids or nutrient additives enhanced plant performance in saline environment, even if the mechanism remains unclear. Other studies have shown that the application of Bacillus subtilis ranked first in alleviating the adverse effects of salinity, if followed by supplemental calcium into a saline nutrient solution (Saleh et al. 2005, p. 30).
To meet future agriculture needs, a solution is an environmentally friendly technique which controls salinisation, uses salt removing crops, chooses halophytes crops for direct salt water irrigation, or selects species that have high salt-removing capacity and commercial value. Some plants can be integrated into rotation programmes or planted as intercrops for perennial plants to control salinisation.
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