Not to be confused with[ edit ] Material stiffness should not be confused with these properties:
The continuous loss of arable land due to irrigation in arid and semiarid regions of the world, overexploitation and mismanagement contribute to global change in a way which currently appears to draw much less concern in the media and the general public than the accumulation of greenhouse gases - carbon dioxide, methane, and others - in our atmosphere and the putative temperature increase and climate changes associated with them.
Nevertheless, the advancement of desertification by salinization and its threatening of global agriculture can be readily quantified. Water is going to be the most cherished resource in this new century, and pessimistic views predict that wars may be fought over it.
We have far advanced from the local runoff farming practiced by the Nabateans in Palestine and up to the 12th century, which was successfully reconstructed by Michael Evenari in the Negev of Israel. It is still practiced by some of the semi-nomads in North Africa e.
Although salt spray in wetlands and coastal areas may cause stress by salinity via the atmosphere, salinity typically is an edaphic stress factor as highlighted by our picture of Halocnemum strobilaceum sitting in a salt crust on the Schott Fedaij in Tunesia.
Hence, we need to understand soil salinity Chapter 2. Natural saline ecosystems then tell us much about types of environments where diverse life forms of plants cope with salinity Chapter 3. This allows both to define eco-physiological problems for study at finer levels of scaling and projects on opportunities and limitations of agro-ecosystems management.
Secondary salinization of agricultural lands is particularly widespread in arid and semiarid environments where crop production requires irrigation schemes. The need for increased food production therefore needs to be met by increases in yield per land area.
To reach this goal, genetic engineering of crop plants for enhanced salt tolerance will be a very important approach. In dry regions where fresh water becomes a scarce commodity, irrigation of moderately salt tolerant crops with brackish water is feasible.
Transgenic lines of some crop species have been generated which can grow and develop at fairly high salinity levels in controlled environments. These transgenics must be tested vigorously for yield potential under field conditions.
Most crops are sensitive to salinity caused by high concentrations of salts in the soil. In addition to this enormous financial cost of production there are other serious impacts of salinity on infrastructure, water supplies, and on social structure and stability of communities.
Environment - Plants - Molecules3— Printed in the Netherlands. Salt tolerant plants may also ameliorate the environment by lowering the water table in salt affected soils.
This book is mainly about the contribution that scientific research has made to understanding basic mechanisms of salt tolerance of plants and progress made to developing salt tolerance in useful agricultural crops in order to make better use of salt affected soils.
That it might be possible to increase salt tolerance of agriculturally useful plants is encouraged by the ability of many flowering plants to live in saline conditions at low water potentials. Mangroves have evolved the ability to grow — and may even require — high levels of salinity.
Salt marsh plants grow with periodic inundation of seawater. Certain plants of the seastrand, and coral islands e. Wedelia biflora have the ability to grow in wide ranges of salinity and water potential caused by periodic droughts as well as salt stress.
Certain semi-arid or arid species e. Atriplex spp are able to tolerate and use salt as an osmoticum, facilitating water extraction from the very low osmotic potentials of desert soils. Within agricultural species there are evident differences in salt tolerance between species and between varieties Chapter 2, Table 9; Maas, In Emanuel Epstein wrote: Unless that premier adaptation is accomplished existence in saline substrates is impossible.
Salinization associated with agriculture occurs when salts build up in the root zone, either because the soil is intrinsically saline, or because the drainage of water from the sub-soil is not sufficient to prevent saline waters rising into the root zone.
It therefore tends to be common in arid and semi arid regions where leaching of salt is poor due to low rainfall; where there are strongly saline sub-soils formed from marine deposits or where irrigation changes water tables and salt flow.anna university, chennai affiliated institutions r - lausannecongress2018.com chemical engineering ii - viii semesters curricula and syllabi semester ii (common to all b.
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Elasticity can be best understood by imaging the atoms are connected by springs.
As we pull on the material, the springs between the atoms get longer and the material lengthens. The elastic portion of the curve is a straight line.