Today the bare rocks of the Montebello islands contain small rockshelter sites which reveal human presence at c. These sites were not used between times and were abandoned when they again became offshore islands. Thus models of changing land-use patterns put forward by arid-region scholars all emphasize mobility and adaptation to changing environmental conditions and suggest small populations thinly spread across the arid zone.
Diets may not have been greatly different from those recorded ethnographically in these regions. They are generally similar and broadly based and included, in addition to marsupials, reptiles, birds, larvae, tubers, fruits, seeds, and aquatic resources where available. Recent claims that grass and tree seeds might have been gathered and processed in the Pleistocene and particularly before the last glacial maximum is notable because although seeds are nutritious, their gathering and processing is laborious.
For this reason, seed processing elsewhere in the world is seen as a key indicator of changes in human behavior connected to the appearance of new technologies, larger and more settled populations and in places the establishment of agriculture.
Its presence in an Australian form in preglacial arid Australia has significant theoretical relevance. Traces of seeds and other plant food remains from Pleistocene levels in Carpenters Gap in the northwest is complemented by pieces of grinding stones dating to c. These carry usewear and residue traces suggesting the processing of starchy and siliceous plants, evidence coincident with a local change to grasslands seen in the pollen record at this time. Data from the Mungo region of western New South Wales indicate how favorable these lake systems were when lacustral conditions ensued. A range of resources—fish, shellfish, crustaceans, and birds—were taken.
Fish may have been taken using nets and spears and possibly traps. A range of mainly small terrestrial game was also captured and again in this region unspecialized grinding tools suggest at least generalized processing of plant foods and seeds during the Pleistocene. When using water with negligible concentration of these elements, they must be added concomitantly with N, P, K and microelements to the recycled solution. Recommended Ca, Mg, SO 4 and Cl concentrations in open and closed irrigation systems for temperate climate countries can be found for various crops in de Kreij et al.
It is still unknown what the optimal concentration of these ions is in recycled solution in arid zones.follow url
Grasses in Arid and Semi-Arid Lands: The Multi-Benefits of the Indigenous Grasses
When both fresh water with high EC and desalinized or rain water are available, the two sources can be mixed so as to result in an EC level below a predefined threshold EC or below specific toxic ion concentration see, e. Raviv et al. The optimal dilution rate should take into account water price and impact on discharge volume.
The dilution strategy should also account for crop susceptibility to salinity at various growth stages. For example, tomato was shown to be more sensitive to salinity stress during the vegetative growth stage than during the reproductive growth stage Mizrahi et al. Desertification refers to land degradation in the global arid zone resulting primarily from various anthropogenic human land use and biophysical factors climatic variations.
Contrary to public opinion, desertification does not refer to the expansion of deserts — although the margins of deserts are known to oscillate north and south owing to natural perturbations in climate and the resulting response of ecosystems. Desertification has occurred because desert ecosystems, which cover over one third of the world's land area, are extremely vulnerable to overexploitation and inappropriate land use, compounded by poverty, political instability, deforestation, overgrazing, and wasteful irrigation practices.
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These people include many of the world's poorest, most marginalized, and politically weak citizens. Although the system above seems like a positive feedback scenario, land degradation and desertification are more likely to operate on a negative feedback method, whereby eventually the system will revert back to its original position albeit having crossed a number of thresholds and experienced a few positive feedbacks during its cyclical journey. Mahdi Gheysari, Gerrit Hoogenboom, in Advances in Agronomy , The water—yield relationship is typically evaluated by the yield response factor K y , which is determined by the slope of a linear function between water stress and yield for the entire duration or a specific development stage of the growing season Vaux and Pruitt, Water use efficiency WUE and irrigation water use efficiency IWUE , on the other hand, are used to assess the amount of productivity i.
Here, WUE is defined as yield per unit area divided by the total water evapotranspirated during the growing season Kg Yield M -3 soil volume Howell, However, only a few studies examined the interaction effect of water balance, stress, and nitrogen fertigation. For example, Eck reported when using DI, water limited the yield of grain maize more than N, in other words, N controlled the yields when water was not limiting, e. They also showed that the water—yield relationship of maize was more linear with higher N applications.
Most of the arable lands in Iran have an arid to semiarid climate Badripour, However, there is no information about the combined effects of water stress and N fertilizer on K y and water efficiency terms of maize under sprinkler irrigation in Iran. Hence, the objectives of this study were to 1 determine the interactions among different levels of water and N fertilizer on WUE, IWUE, on the yield response factor to water K y for silage maize grown under sprinkler irrigation in a semiarid region, 2 outline how best community practices are manifest into an experimental design, 3 provide management guidelines to regional growers and irrigation agencies to water management programs for maize in the region, and 4 provide a synthesis of the controls on cultivated maize production from arid and semiarid regions.
Srinivasa Rao, Singh, in Advances in Agronomy , Livestock-based farming systems make significant contribution for livelihood security of farmers particularly in arid zone of India. Although arid zones are less suitable for crop production due to inherent soil constraints, some grasses and tree species of forage value and economic importance can grow well and help in augmenting forage production. Interventions in low rainfall regions focused on enhancing the availability of fodders and its quality, improving shelter for alleviating the heat stress in animals, introducing improved breeds of small ruminants, improving the health of animals as better health makes animals more tolerant to climatic stresses Kinyangi et al.
In high rainfall regions, the emphasis was on enhancing the productivity of animals and returns from the livestock by cultivation of high biomass producing improved fodder varieties for enhancing the green fodder production, and efficient recycling of resources by development of farming system—based models.
Arid areas absorb unexpected amounts of atmospheric carbon
Alhadrami, B. Faye, in Reference Module in Food Science , Camel milk is one of the most valuable food resources for the people living in arid and semiarid zones. Most of the camel milk is consumed as fresh milk. Kenyan researchers have shown that the quality of susa could be improved using selected mesophilic starter cultures rather than spontaneous fermentation; the resulting fermented milk has a uniform taste and a longer shelf life.
This beverage is sometimes enriched with spices or garlic. It can be preserved for some time without losing its properties. Some researchers have claimed that shubat can be used to cure tuberculosis and some gastric and intestinal diseases. Holzapfel, in Encyclopedia of Ecology , Even though obviously not readily observable, microorganisms inhabit all desert areas and in the extreme arid zones are often the only life forms present.
Relatively little is known about the diversity within the lower three kingdoms Fungi, Protista, Monera in general and even less is known about the species richness of these groups in deserts. Since factors other than water availability are more important chiefly soil pH in determining microbial diversity, it can be assumed that true desert can be quite rich as well. Mycorrhizal fungi seem to be quite important in desert ecosystems, as in more mesic ecosystems. It appears that mycorrhizae of desert plants not only supply the plants with nutrients but also supply moisture during the dry season, at times taking the place of root hairs.
Studies conducted in the Chihuahuan Desert indicated that most dominant, perennial species have high arbuscular AM fungal infection rates in their coarse roots system, while fine-rooted annual species in comparison show much lower infection rates and are also much less dependent on mycorrhizal associations in general.
Worth mentioning are mycorrhizal desert truffles Terfezia and Tirmania : Ascomycetes , that are host specific to Helianthemum species in the arid region of the Middle East and the Mediterranean zones of the Old World. The desert of the American West supports an elusive community of aboveground observable fungi in which the Gasteromycetes puffballs and allies figure predominately. Another common example is Podaxis psitillaris desert shaggy mane , a species most common in sandy deserts. Except for their crucial part in mycorrhizal associations, desert microorganisms are noteworthy for their role in three typical desert phenomena: desert crusts, desert varnish, and interstitial communities.
Desert crusts are microbiotic communities composed of drought and heat-tolerant algae, cyanobacteria, fungi, lichen, and mosses. These often species-rich communities are held together by sticky polysaccharide secretions and thus form surface crusts. Desiccated crusts are often indiscernible until rainfall or dew moistens the surface and microbial communities become active and green. Under extreme conditions, such crusts can form below the surface.
The most common life form in crusts and in some areas also in hot deserts in general is cyanobacteria. Among their roles in the desert ecosystem are atmospheric fixation of nitrogen and the binding of soil particles. Together with mineral-reducing bacteria, the cyanobacteria are important in soil fertilization and soil formation and thereby have clearly important effects on vascular plants and dependent animal consumers. In hot deserts, cyanobacterial crusts often form smooth surfaces, while in cold deserts, where crust forming interacts with frost heaving, a very rough surface is typical.
These different surface types clearly affect vascular plants differently. Even exposed desert rocks can support life. Clearly the most visible organisms are crustose lichens.
Ecology and Society: Sustainable Small-Scale Agriculture in Semi-Arid Environments
However, when conditions become too extreme for growth of lichens, bacteria can still survive on the surface of rocks. Desert varnish, the dark and shiny surface found on sun-exposed, porous stones in hot deserts, is the result of bacterial activity. These bacterial colonies obtain energy from inorganic and organic substances and trap submicroscopic, wind-borne clay particles.
These particles accumulate in a thin layer and act as sun protection. Over very long time periods, estimated at thousands of years, these bacterial communities oxidize wind-blown manganese and iron particles and when baked together with clay particles form the dark desert varnish.
The color of desert varnish varies depending on the relative proportion of oxidized manganese dark black to iron reddish. Environmental conditions even more extreme than those that support surface bacterial growth can still allow the formation of interstitial communities.
These communities can stay dormant for long periods of time and inhabit hot and cold deserts alike they are known to exist on exposed rocks in Antarctica. Abdelghani Chakhchar, The argan tree Argania spinosa plays a crucial socioeconomic and ecological role in southwestern Morocco's arid and semiarid zones. Pot study was undertaken to understand and characterize the physiological and biochemical tolerance mechanisms of this endemic species to drought stress. This is a zone of high air pressure where the air sinks. Air at the equator rises and cools - condensation then forms rain.
This air is dry and no condensation can form, so there is no rain. This is known as the Hadley Cell. It shows how air moves around the atmosphere near the equator and tropics. Some deserts are found on the western edges of continents. They are caused by cold ocean currents, which run along the coast.
They cool the air and make it harder for the air to hold moisture. Most moisture falls as rain before it reaches the land, eg the Namib Desert in Africa.